{"version":"1.0.0","segments":[{"startTime":0.33,"endTime":1.47,"body":"- Well, good evening, everybody."},{"startTime":1.47,"endTime":2.37,"body":"Thank you very much."},{"startTime":2.37,"endTime":6.42,"body":"Welcome to the second"},{"startTime":2.37,"endTime":6.42,"body":"Gresham lecture on net zero."},{"startTime":6.42,"endTime":8.43,"body":"I'm Myles Allen, the Frank Jackson"},{"startTime":8.43,"endTime":11.28,"body":"Professor of the Environment"},{"startTime":8.43,"endTime":11.28,"body":"at Gresham College,"},{"startTime":11.28,"endTime":14.49,"body":"and I'm also a professor at"},{"startTime":11.28,"endTime":14.49,"body":"the University of Oxford,"},{"startTime":14.49,"endTime":16.8,"body":"and today I'm talking to you"},{"startTime":16.8,"endTime":20.67,"body":"about the atmospheric"},{"startTime":16.8,"endTime":20.67,"body":"physics behind net zero."},{"startTime":20.67,"endTime":22.95,"body":"At the beginning of the last lecture,"},{"startTime":22.95,"endTime":26.97,"body":"I talked to you about how"},{"startTime":22.95,"endTime":26.97,"body":"different ways in which climate,"},{"startTime":26.97,"endTime":30.03,"body":"in which science in general makes progress"},{"startTime":30.03,"endTime":34.2,"body":"by chance, by design, by"},{"startTime":30.03,"endTime":34.2,"body":"just changing the subject,"},{"startTime":34.2,"endTime":37.05,"body":"and in this one, I'm"},{"startTime":34.2,"endTime":37.05,"body":"going to talk a little bit"},{"startTime":37.05,"endTime":41.61,"body":"about how occasionally"},{"startTime":37.05,"endTime":41.61,"body":"science doesn't make progress"},{"startTime":41.61,"endTime":42.78,"body":"for interesting reasons."},{"startTime":42.78,"endTime":45.24,"body":"We sort of get stuck for a bit,"},{"startTime":45.24,"endTime":48.21,"body":"and there's a couple of instances"},{"startTime":48.21,"endTime":53.21,"body":"of how we've got stuck in"},{"startTime":48.21,"endTime":53.21,"body":"the history of net zero,"},{"startTime":53.58,"endTime":55.95,"body":"which I'll be talking about today."},{"startTime":55.95,"endTime":59.16,"body":"A lot of this history"},{"startTime":55.95,"endTime":59.16,"body":"goes back a long way,"},{"startTime":59.16,"endTime":61.89,"body":"all the way back to the 19th century."},{"startTime":61.89,"endTime":63.84,"body":"Joseph Fourier, familiar to mathematicians"},{"startTime":63.84,"endTime":66.87,"body":"as the person behind Fourier transforms,"},{"startTime":66.87,"endTime":68.97,"body":"Eunice Foote, less well known,"},{"startTime":68.97,"endTime":71.64,"body":"but I'll talk about her in"},{"startTime":68.97,"endTime":71.64,"body":"a minute, and John Tyndall,"},{"startTime":71.64,"endTime":76.35,"body":"these were thinkers in the"},{"startTime":71.64,"endTime":76.35,"body":"early to mid 19th century"},{"startTime":76.35,"endTime":78.33,"body":"who were fascinated by the fact"},{"startTime":78.33,"endTime":81.66,"body":"that there was an"},{"startTime":78.33,"endTime":81.66,"body":"invisible light out there,"},{"startTime":81.66,"endTime":84.36,"body":"infrared light that you couldn't see"},{"startTime":84.36,"endTime":88.02,"body":"but which behaved in the"},{"startTime":84.36,"endTime":88.02,"body":"same way as visible light,"},{"startTime":88.02,"endTime":90.22,"body":"and they were fascinated"},{"startTime":88.02,"endTime":90.22,"body":"by this phenomenon."},{"startTime":91.62,"endTime":96.45,"body":"Joseph Fourier speculated"},{"startTime":91.62,"endTime":96.45,"body":"without any evidence whatsoever,"},{"startTime":96.45,"endTime":99.42,"body":"it's interesting how he sort"},{"startTime":96.45,"endTime":99.42,"body":"of came up with the idea,"},{"startTime":99.42,"endTime":102.57,"body":"that it was actually"},{"startTime":99.42,"endTime":102.57,"body":"gases in the atmosphere"},{"startTime":102.57,"endTime":105.75,"body":"that were responsible for"},{"startTime":102.57,"endTime":105.75,"body":"keeping the Earth warm,"},{"startTime":105.75,"endTime":107.61,"body":"'cause they were able to"},{"startTime":105.75,"endTime":107.61,"body":"work out the temperature"},{"startTime":107.61,"endTime":110.7,"body":"the planet would be if"},{"startTime":107.61,"endTime":110.7,"body":"we had no atmosphere,"},{"startTime":110.7,"endTime":115.7,"body":"and hence is credited with"},{"startTime":110.7,"endTime":115.7,"body":"having sort of come up"},{"startTime":116.22,"endTime":118.14,"body":"with the greenhouse effect originally."},{"startTime":118.14,"endTime":121.56,"body":"Eunice Foote was an American woman"},{"startTime":121.56,"endTime":125.4,"body":"who presented a paper of circumstances"},{"startTime":125.4,"endTime":127.95,"body":"affecting the heat of the sun's rays,"},{"startTime":127.95,"endTime":131.49,"body":"which was the first"},{"startTime":127.95,"endTime":131.49,"body":"empirical demonstration"},{"startTime":131.49,"endTime":133.65,"body":"of the fact that different gases"},{"startTime":133.65,"endTime":135.78,"body":"have a different impact on temperature,"},{"startTime":135.78,"endTime":137.88,"body":"and she showed that carbon"},{"startTime":135.78,"endTime":137.88,"body":"dioxide in particular"},{"startTime":137.88,"endTime":140.973,"body":"was particularly effective"},{"startTime":137.88,"endTime":140.973,"body":"at keeping things warm."},{"startTime":141.9,"endTime":144.78,"body":"Interestingly, I'm afraid I"},{"startTime":141.9,"endTime":144.78,"body":"don't have a picture of her."},{"startTime":144.78,"endTime":146.76,"body":"We don't have a picture"},{"startTime":144.78,"endTime":146.76,"body":"of her says something"},{"startTime":146.76,"endTime":150.0,"body":"about 19th century science, doesn't it?"},{"startTime":150.0,"endTime":153.81,"body":"And also, she never got to read her paper."},{"startTime":153.81,"endTime":155.79,"body":"Her husband had to read it for her"},{"startTime":155.79,"endTime":158.1,"body":"to the American Chemical Society."},{"startTime":158.1,"endTime":160.29,"body":"Fortunately, things have moved on,"},{"startTime":160.29,"endTime":163.23,"body":"but we can also bicker a little bit"},{"startTime":163.23,"endTime":165.45,"body":"about whether she demonstrated"},{"startTime":163.23,"endTime":165.45,"body":"the greenhouse vapor."},{"startTime":165.45,"endTime":168.78,"body":"She definitely demonstrated"},{"startTime":165.45,"endTime":168.78,"body":"a different impact"},{"startTime":168.78,"endTime":172.26,"body":"of carbon dioxide and water"},{"startTime":168.78,"endTime":172.26,"body":"vapor compared to, say,"},{"startTime":172.26,"endTime":175.86,"body":"dry air in affecting the"},{"startTime":172.26,"endTime":175.86,"body":"heat of the sun's rays."},{"startTime":175.86,"endTime":178.56,"body":"But the man who just a few years later,"},{"startTime":178.56,"endTime":180.78,"body":"because of, there was"},{"startTime":178.56,"endTime":180.78,"body":"no internet back then,"},{"startTime":180.78,"endTime":183.63,"body":"so he can't have known of"},{"startTime":180.78,"endTime":183.63,"body":"Eunice Foote's experiments,"},{"startTime":183.63,"endTime":187.35,"body":"an Irishman called John"},{"startTime":183.63,"endTime":187.35,"body":"Tyndall on the right here"},{"startTime":187.35,"endTime":189.75,"body":"was the first to really demonstrate"},{"startTime":189.75,"endTime":194.22,"body":"how gases affect infrared light."},{"startTime":194.22,"endTime":197.04,"body":"And he did a number of"},{"startTime":194.22,"endTime":197.04,"body":"really elegant experiments"},{"startTime":197.04,"endTime":200.85,"body":"and left us some beautiful"},{"startTime":197.04,"endTime":200.85,"body":"drawings of his experiments,"},{"startTime":200.85,"endTime":204.27,"body":"including this one in which,"},{"startTime":200.85,"endTime":204.27,"body":"if you look on the right here,"},{"startTime":204.27,"endTime":208.47,"body":"you can see it's labeled C on the diagram,"},{"startTime":208.47,"endTime":211.83,"body":"there's a block of metal or something"},{"startTime":211.83,"endTime":215.7,"body":"which is being heated by"},{"startTime":211.83,"endTime":215.7,"body":"a gas flame underneath it."},{"startTime":215.7,"endTime":220.7,"body":"And the heat, the infrared"},{"startTime":215.7,"endTime":220.7,"body":"light from that hot body"},{"startTime":221.7,"endTime":223.83,"body":"is going through that long pipe"},{"startTime":223.83,"endTime":225.78,"body":"and being measured by that thermopile,"},{"startTime":225.78,"endTime":228.48,"body":"the two sort of cones at the other end,"},{"startTime":228.48,"endTime":231.9,"body":"and he's passing gases through the pipe"},{"startTime":231.9,"endTime":234.0,"body":"to see what the gases did"},{"startTime":234.0,"endTime":237.123,"body":"to the passage of the infrared light."},{"startTime":238.14,"endTime":240.3,"body":"And what he was able to show"},{"startTime":240.3,"endTime":242.73,"body":"with this very ingenious experiment"},{"startTime":242.73,"endTime":245.4,"body":"was that even if you"},{"startTime":242.73,"endTime":245.4,"body":"could see through the gas"},{"startTime":245.4,"endTime":249.51,"body":"perfectly well with your"},{"startTime":245.4,"endTime":249.51,"body":"eyes, for the infrared light,"},{"startTime":249.51,"endTime":252.36,"body":"it made a huge difference what"},{"startTime":249.51,"endTime":252.36,"body":"gases he put into the pipe,"},{"startTime":252.36,"endTime":254.7,"body":"and in particular, he"},{"startTime":252.36,"endTime":254.7,"body":"showed that carbon dioxide"},{"startTime":254.7,"endTime":258.213,"body":"was a very effective"},{"startTime":254.7,"endTime":258.213,"body":"blocker of infrared light."},{"startTime":259.29,"endTime":262.05,"body":"And it was then his experiments"},{"startTime":262.05,"endTime":265.05,"body":"that were taken up by another"},{"startTime":262.05,"endTime":265.05,"body":"19th century scientist,"},{"startTime":265.05,"endTime":268.38,"body":"this time a Swede, Svante Arrhenius,"},{"startTime":268.38,"endTime":272.19,"body":"who actually gave the"},{"startTime":268.38,"endTime":272.19,"body":"first quantitative account"},{"startTime":272.19,"endTime":274.86,"body":"of the impact of increasing carbon dioxide"},{"startTime":274.86,"endTime":276.03,"body":"on global temperatures."},{"startTime":276.03,"endTime":277.95,"body":"So Arrhenius, and this is a quote,"},{"startTime":277.95,"endTime":279.18,"body":"well, his paper was in German,"},{"startTime":279.18,"endTime":281.167,"body":"but this is a quote from his paper."},{"startTime":281.167,"endTime":284.94,"body":"\"Any doubling of the percentage"},{"startTime":281.167,"endTime":284.94,"body":"of carbon dioxide in the air"},{"startTime":284.94,"endTime":288.54,"body":"would raise the earth's"},{"startTime":284.94,"endTime":288.54,"body":"temperature by four degrees,"},{"startTime":288.54,"endTime":291.03,"body":"and if the carbon dioxide"},{"startTime":288.54,"endTime":291.03,"body":"were increased fourfold,"},{"startTime":291.03,"endTime":292.86,"body":"it would increase temperature"},{"startTime":291.03,"endTime":292.86,"body":"by eight degrees.\""},{"startTime":292.86,"endTime":294.09,"body":"It almost reads like a sentence"},{"startTime":294.09,"endTime":296.193,"body":"out of a modern climate science paper."},{"startTime":297.27,"endTime":300.06,"body":"This was 1898, so it's extraordinary"},{"startTime":300.06,"endTime":302.643,"body":"how long ago we've understood this."},{"startTime":304.17,"endTime":306.04,"body":"Interestingly, Arrhenius"},{"startTime":304.17,"endTime":306.04,"body":"thought this would take"},{"startTime":306.04,"endTime":308.37,"body":"1,000 years or so, 'cause of"},{"startTime":306.04,"endTime":308.37,"body":"course he couldn't possibly"},{"startTime":308.37,"endTime":311.37,"body":"anticipate that coal, oil,"},{"startTime":308.37,"endTime":311.37,"body":"and gas use would explode."},{"startTime":311.37,"endTime":314.19,"body":"I mean, oil and gas use wasn't"},{"startTime":311.37,"endTime":314.19,"body":"really a thing back then."},{"startTime":314.19,"endTime":316.95,"body":"Coal was the fuel of the time."},{"startTime":316.95,"endTime":318.93,"body":"And he thought it might"},{"startTime":316.95,"endTime":318.93,"body":"take 1,000 years to happen."},{"startTime":318.93,"endTime":320.1,"body":"He also, being a Swede,"},{"startTime":320.1,"endTime":322.383,"body":"thought it'd be a good"},{"startTime":320.1,"endTime":322.383,"body":"thing, interestingly."},{"startTime":323.34,"endTime":326.13,"body":"So again, attitudes have changed."},{"startTime":326.13,"endTime":328.14,"body":"But what's really interesting"},{"startTime":326.13,"endTime":328.14,"body":"from the point of view"},{"startTime":328.14,"endTime":330.12,"body":"of the science is that unfortunately"},{"startTime":330.12,"endTime":332.52,"body":"Arrhenius didn't really"},{"startTime":330.12,"endTime":332.52,"body":"get to bask in the glory"},{"startTime":332.52,"endTime":336.3,"body":"of his discovery or his, for very long,"},{"startTime":336.3,"endTime":339.54,"body":"because another Swede, an"},{"startTime":336.3,"endTime":339.54,"body":"even more famous Swede,"},{"startTime":339.54,"endTime":341.31,"body":"intervened, Angstrom,"},{"startTime":341.31,"endTime":343.62,"body":"someone who'd be very"},{"startTime":341.31,"endTime":343.62,"body":"well known to any chemist."},{"startTime":343.62,"endTime":346.71,"body":"He actually has a unit named"},{"startTime":343.62,"endTime":346.71,"body":"after him, the Angstrom."},{"startTime":346.71,"endTime":350.01,"body":"And what Angstrom did"},{"startTime":346.71,"endTime":350.01,"body":"was he was very skeptical"},{"startTime":350.01,"endTime":354.36,"body":"about Arrhenius's ideas about"},{"startTime":350.01,"endTime":354.36,"body":"carbon dioxide and climate,"},{"startTime":354.36,"endTime":357.81,"body":"so he repeated Tyndall's experiment,"},{"startTime":357.81,"endTime":361.86,"body":"and he worked out that"},{"startTime":357.81,"endTime":361.86,"body":"between him and space"},{"startTime":361.86,"endTime":366.06,"body":"was about two meters of carbon dioxide."},{"startTime":366.06,"endTime":368.4,"body":"If you took all the carbon"},{"startTime":366.06,"endTime":368.4,"body":"dioxide in the atmosphere"},{"startTime":368.4,"endTime":370.02,"body":"and brought it down to the surface,"},{"startTime":370.02,"endTime":373.38,"body":"so you had pure carbon dioxide"},{"startTime":370.02,"endTime":373.38,"body":"and no carbon dioxide beyond,"},{"startTime":373.38,"endTime":375.78,"body":"it's about two meters"},{"startTime":373.38,"endTime":375.78,"body":"before you make a note."},{"startTime":375.78,"endTime":378.45,"body":"It's about three meters now. There you go."},{"startTime":378.45,"endTime":380.79,"body":"Stuff's been happening since then."},{"startTime":380.79,"endTime":382.8,"body":"But back then, so two meters."},{"startTime":382.8,"endTime":386.55,"body":"And he also knew that it"},{"startTime":382.8,"endTime":386.55,"body":"did, I mean, you know,"},{"startTime":386.55,"endTime":389.49,"body":"they understood the"},{"startTime":386.55,"endTime":389.49,"body":"absorption of infrared light"},{"startTime":389.49,"endTime":391.86,"body":"in gases quite well by this stage,"},{"startTime":391.86,"endTime":393.9,"body":"and he understood it didn't really matter"},{"startTime":393.9,"endTime":395.94,"body":"how long the path was."},{"startTime":395.94,"endTime":398.583,"body":"What mattered with the"},{"startTime":395.94,"endTime":398.583,"body":"amount of stuff in the way."},{"startTime":400.35,"endTime":402.453,"body":"If that sounds implausible to you,"},{"startTime":403.65,"endTime":405.21,"body":"I hope you'll forgive"},{"startTime":403.65,"endTime":405.21,"body":"this particular analogy,"},{"startTime":405.21,"endTime":406.68,"body":"but I find it does work."},{"startTime":406.68,"endTime":410.61,"body":"If you pee in a bucket,"},{"startTime":406.68,"endTime":410.61,"body":"the color looking down"},{"startTime":410.61,"endTime":412.35,"body":"through the bucket doesn't depend"},{"startTime":412.35,"endTime":414.2,"body":"on the amount of water in the bucket."},{"startTime":416.34,"endTime":418.41,"body":"Now, you can all go and"},{"startTime":416.34,"endTime":418.41,"body":"try this out at home"},{"startTime":418.41,"endTime":420.09,"body":"if you don't believe me."},{"startTime":418.41,"endTime":420.09,"body":"(audience laughs)"},{"startTime":420.09,"endTime":422.373,"body":"Don't try it out here, but some,"},{"startTime":423.42,"endTime":425.13,"body":"but it's true, so in other words,"},{"startTime":425.13,"endTime":426.12,"body":"it's sort of the equivalent."},{"startTime":426.12,"endTime":429.817,"body":"He's bringing the carbon dioxide in,"},{"startTime":429.817,"endTime":432.09,"body":"you know, all the way down to the surface,"},{"startTime":432.09,"endTime":433.68,"body":"and then checking to see,"},{"startTime":432.09,"endTime":433.68,"body":"okay, how much carbon,"},{"startTime":433.68,"endTime":436.56,"body":"how much infrared light"},{"startTime":433.68,"endTime":436.56,"body":"is it actually absorbing?"},{"startTime":436.56,"endTime":438.087,"body":"And what he found was that when he took"},{"startTime":438.087,"endTime":440.4,"body":"the sort of right amount"},{"startTime":438.087,"endTime":440.4,"body":"of carbon dioxide,"},{"startTime":440.4,"endTime":442.08,"body":"the amount between us and space,"},{"startTime":442.08,"endTime":445.313,"body":"it's, well, it's 0.04% now."},{"startTime":447.437,"endTime":451.6,"body":"It was 0.03, less than 0.03% back then."},{"startTime":453.27,"endTime":457.563,"body":"And he found that none of the"},{"startTime":453.27,"endTime":457.563,"body":"infrared line got through."},{"startTime":458.49,"endTime":461.22,"body":"And if he doubled it, still"},{"startTime":458.49,"endTime":461.22,"body":"none of it got through."},{"startTime":461.22,"endTime":462.84,"body":"So he said, \"Well, there you go.\""},{"startTime":462.84,"endTime":464.91,"body":"And if you added water vapor,"},{"startTime":462.84,"endTime":464.91,"body":"even less of it got through."},{"startTime":464.91,"endTime":466.56,"body":"I mean, it's a tiny amount got through,"},{"startTime":466.56,"endTime":468.63,"body":"and with the water vapor in as well,"},{"startTime":468.63,"endTime":470.04,"body":"it made no difference whatsoever."},{"startTime":470.04,"endTime":473.16,"body":"So he then published a paper"},{"startTime":473.16,"endTime":475.53,"body":"saying, \"Well, Arrhenius"},{"startTime":473.16,"endTime":475.53,"body":"was obviously wrong,"},{"startTime":475.53,"endTime":478.71,"body":"interesting idea, but actually"},{"startTime":475.53,"endTime":478.71,"body":"all of the infrared light"},{"startTime":478.71,"endTime":479.88,"body":"gets absorbed by the carbon dioxide,"},{"startTime":479.88,"endTime":480.96,"body":"so adding more carbon dioxide"},{"startTime":480.96,"endTime":482.58,"body":"can't possibly make any difference,\""},{"startTime":482.58,"endTime":485.427,"body":"so the CO2 theory is rubbish.\""},{"startTime":486.27,"endTime":487.65,"body":"Sounds very plausible."},{"startTime":487.65,"endTime":490.47,"body":"In fact, it was completely successful"},{"startTime":490.47,"endTime":493.278,"body":"as a debunk of Arrhenius's theory."},{"startTime":493.278,"endTime":495.66,"body":"For 50 years, people forgot all about it."},{"startTime":495.66,"endTime":498.72,"body":"So poor old Arrhenius went"},{"startTime":495.66,"endTime":498.72,"body":"to his grave with no idea"},{"startTime":498.72,"endTime":501.22,"body":"that he'd actually discovered"},{"startTime":498.72,"endTime":501.22,"body":"something important."},{"startTime":503.16,"endTime":507.33,"body":"And actually more, sort of personally,"},{"startTime":507.33,"endTime":510.16,"body":"this is important to me"},{"startTime":507.33,"endTime":510.16,"body":"because every now and then"},{"startTime":512.318,"endTime":513.42,"body":"a physicist somewhere in the world"},{"startTime":513.42,"endTime":515.67,"body":"sort of rediscovers Angstrom's argument"},{"startTime":515.67,"endTime":517.95,"body":"and writes me an angry email"},{"startTime":517.95,"endTime":519.66,"body":"saying, \"Climate scientists"},{"startTime":517.95,"endTime":519.66,"body":"are all incompetent."},{"startTime":519.66,"endTime":522.203,"body":"You obviously haven't thought"},{"startTime":519.66,"endTime":522.203,"body":"about band saturation,"},{"startTime":523.295,"endTime":526.53,"body":"and so, you know, global"},{"startTime":523.295,"endTime":526.53,"body":"warming is not caused"},{"startTime":526.53,"endTime":528.12,"body":"by rising carbon dioxide.\""},{"startTime":528.12,"endTime":530.19,"body":"And it's sort of understandable"},{"startTime":530.19,"endTime":531.54,"body":"that people have this confusion,"},{"startTime":531.54,"endTime":533.22,"body":"because if we go to, you know,"},{"startTime":533.22,"endTime":534.93,"body":"apologies to \"Encyclopaedia Britannica,\""},{"startTime":534.93,"endTime":536.46,"body":"but they're supposed to get things right."},{"startTime":536.46,"endTime":540.57,"body":"I mean, and this is not an"},{"startTime":536.46,"endTime":540.57,"body":"uncommon picture out there."},{"startTime":540.57,"endTime":542.897,"body":"This is sort of the standard"},{"startTime":540.57,"endTime":542.897,"body":"schoolbook picture we have"},{"startTime":542.897,"endTime":545.16,"body":"of how the greenhouse effect works,"},{"startTime":545.16,"endTime":549.39,"body":"and what it implies is"},{"startTime":545.16,"endTime":549.39,"body":"that the infrared opacity"},{"startTime":549.39,"endTime":552.54,"body":"of the atmosphere, sort of"},{"startTime":549.39,"endTime":552.54,"body":"the amount of infrared light"},{"startTime":552.54,"endTime":554.7,"body":"that gets through the atmosphere to space,"},{"startTime":554.7,"endTime":558.033,"body":"somehow determines the"},{"startTime":554.7,"endTime":558.033,"body":"Earth's surface temperature."},{"startTime":559.59,"endTime":562.59,"body":"I mean, Angstrom couldn't"},{"startTime":559.59,"endTime":562.59,"body":"do this, but we can now."},{"startTime":562.59,"endTime":565.83,"body":"If we look at the planet in the infrared"},{"startTime":565.83,"endTime":569.16,"body":"from space, what's impressive,"},{"startTime":569.16,"endTime":571.74,"body":"well, it's a tremendously"},{"startTime":569.16,"endTime":571.74,"body":"impressive movie."},{"startTime":571.74,"endTime":576.74,"body":"You can see the daily cycle"},{"startTime":571.74,"endTime":576.74,"body":"of cloudiness over somewhere."},{"startTime":577.02,"endTime":579.84,"body":"You can see the swirls of weather motions"},{"startTime":579.84,"endTime":580.92,"body":"in the atmosphere and so on."},{"startTime":580.92,"endTime":584.49,"body":"But what you can't see is the surface."},{"startTime":584.49,"endTime":586.02,"body":"Angstrom was right."},{"startTime":586.02,"endTime":588.307,"body":"The atmosphere is"},{"startTime":586.02,"endTime":588.307,"body":"completely opaque as far as,"},{"startTime":588.307,"endTime":590.7,"body":"you know, for all practical purposes,"},{"startTime":590.7,"endTime":594.09,"body":"the atmosphere is opaque in the infrared."},{"startTime":594.09,"endTime":595.74,"body":"So at this point, when I'm"},{"startTime":594.09,"endTime":595.74,"body":"giving this lecture to students,"},{"startTime":595.74,"endTime":597.72,"body":"some of them will start sort"},{"startTime":595.74,"endTime":597.72,"body":"of shifting in their seats"},{"startTime":597.72,"endTime":600.459,"body":"and wondering if I'm sponsored"},{"startTime":597.72,"endTime":600.459,"body":"by a major oil corporation."},{"startTime":600.459,"endTime":601.522,"body":"(audience laughs)"},{"startTime":601.522,"endTime":603.51,"body":"But I'm now going to"},{"startTime":601.522,"endTime":603.51,"body":"tell you before you leave"},{"startTime":603.51,"endTime":605.88,"body":"or sort of switch off"},{"startTime":603.51,"endTime":605.88,"body":"and decide that we don't,"},{"startTime":605.88,"endTime":608.1,"body":"global warming's not a thing,"},{"startTime":608.1,"endTime":611.22,"body":"I'm now going to tell you"},{"startTime":608.1,"endTime":611.22,"body":"how it actually does work"},{"startTime":611.22,"endTime":613.26,"body":"because it's not that"},{"startTime":611.22,"endTime":613.26,"body":"much more complicated."},{"startTime":613.26,"endTime":618.15,"body":"We just have to think about"},{"startTime":613.26,"endTime":618.15,"body":"the way carbon dioxide works"},{"startTime":618.15,"endTime":620.61,"body":"in the atmosphere, the way"},{"startTime":618.15,"endTime":620.61,"body":"the atmosphere works as well"},{"startTime":620.61,"endTime":622.17,"body":"underneath the carbon, you know,"},{"startTime":622.17,"endTime":623.79,"body":"holding the carbon dioxide."},{"startTime":623.79,"endTime":625.53,"body":"Carbon dioxide's well mixed"},{"startTime":623.79,"endTime":625.53,"body":"through the atmosphere."},{"startTime":625.53,"endTime":628.43,"body":"If you put carbon dioxide into"},{"startTime":625.53,"endTime":628.43,"body":"the atmosphere, it's mixed,"},{"startTime":629.351,"endTime":631.62,"body":"the proportion of air"},{"startTime":629.351,"endTime":631.62,"body":"that is carbon dioxide"},{"startTime":631.62,"endTime":635.82,"body":"is the same wherever you are,"},{"startTime":631.62,"endTime":635.82,"body":"whatever altitude you're at."},{"startTime":635.82,"endTime":640.82,"body":"So if I just take a chunk of"},{"startTime":635.82,"endTime":640.82,"body":"atmosphere, a square column,"},{"startTime":641.7,"endTime":644.58,"body":"and I represent carbon dioxide molecules"},{"startTime":644.58,"endTime":647.76,"body":"by these colored balls"},{"startTime":644.58,"endTime":647.76,"body":"where the temperature"},{"startTime":647.76,"endTime":651.27,"body":"of the molecules is"},{"startTime":647.76,"endTime":651.27,"body":"indicated by the color,"},{"startTime":651.27,"endTime":654.0,"body":"and the absorption density,"},{"startTime":654.0,"endTime":655.86,"body":"which is pretty close to the density,"},{"startTime":655.86,"endTime":657.54,"body":"but it just varies a little bit faster,"},{"startTime":657.54,"endTime":660.36,"body":"that's a sort of, kind of a detail,"},{"startTime":660.36,"endTime":663.36,"body":"is indicated by the density, okay?"},{"startTime":663.36,"endTime":664.8,"body":"So you can see what I'm driving at here."},{"startTime":664.8,"endTime":666.24,"body":"Before I go any further,"},{"startTime":666.24,"endTime":669.72,"body":"the depth of the atmosphere"},{"startTime":666.24,"endTime":669.72,"body":"is many kilometers,"},{"startTime":669.72,"endTime":671.1,"body":"so these colored balls"},{"startTime":671.1,"endTime":674.073,"body":"are sort of hundreds of meters across."},{"startTime":675.63,"endTime":678.36,"body":"I made this graphic to give a presentation"},{"startTime":678.36,"endTime":679.95,"body":"to a San Francisco court,"},{"startTime":679.95,"endTime":681.48,"body":"'cause I was tasked with explaining"},{"startTime":681.48,"endTime":683.61,"body":"how the greenhouse effect"},{"startTime":681.48,"endTime":683.61,"body":"works to the court,"},{"startTime":683.61,"endTime":685.92,"body":"and afterwards, Rush Limbaugh,"},{"startTime":685.92,"endTime":690.92,"body":"a very strong-willed"},{"startTime":685.92,"endTime":690.92,"body":"radio host in America,"},{"startTime":691.17,"endTime":692.774,"body":"got very angry about the fact"},{"startTime":692.774,"endTime":694.02,"body":"that I was a typical climate scientist"},{"startTime":694.02,"endTime":696.96,"body":"exaggerating the problem,"},{"startTime":694.02,"endTime":696.96,"body":"making out these molecules"},{"startTime":696.96,"endTime":699.381,"body":"are much bigger than they are."},{"startTime":699.381,"endTime":700.38,"body":"(audience laughs)"},{"startTime":699.381,"endTime":700.38,"body":"So I should warn you,"},{"startTime":700.38,"endTime":702.393,"body":"molecules are not to scale."},{"startTime":704.79,"endTime":707.07,"body":"I'm showing you what they do."},{"startTime":707.07,"endTime":710.04,"body":"Here we are, temperature and density"},{"startTime":710.04,"endTime":712.59,"body":"of carbon dioxide molecules"},{"startTime":710.04,"endTime":712.59,"body":"both decrease with height."},{"startTime":712.59,"endTime":715.15,"body":"So if we look from the side, you can see"},{"startTime":717.649,"endTime":719.7,"body":"that progression as you go"},{"startTime":717.649,"endTime":719.7,"body":"up through the atmosphere."},{"startTime":719.7,"endTime":722.4,"body":"It gets colder, we all know why"},{"startTime":719.7,"endTime":722.4,"body":"it gets colder, with height."},{"startTime":722.4,"endTime":724.62,"body":"You've all experienced that"},{"startTime":722.4,"endTime":724.62,"body":"if you've climbed a mountain."},{"startTime":724.62,"endTime":727.41,"body":"Roughly sort of six degrees"},{"startTime":724.62,"endTime":727.41,"body":"or so per kilometer,"},{"startTime":727.41,"endTime":729.56,"body":"as you climb the"},{"startTime":727.41,"endTime":729.56,"body":"mountain, air gets colder."},{"startTime":730.98,"endTime":732.09,"body":"And the density likewise,"},{"startTime":732.09,"endTime":733.8,"body":"'cause air is sitting"},{"startTime":732.09,"endTime":733.8,"body":"under its own weight."},{"startTime":733.8,"endTime":736.62,"body":"So as you go up through the atmosphere,"},{"startTime":736.62,"endTime":738.363,"body":"the density falls off as well."},{"startTime":739.92,"endTime":741.12,"body":"Now, imagine what's going to happen"},{"startTime":741.12,"endTime":745.91,"body":"if you look down at this"},{"startTime":741.12,"endTime":745.91,"body":"sort of ball pit from above."},{"startTime":747.48,"endTime":750.06,"body":"Well, here's the actual view."},{"startTime":750.06,"endTime":753.51,"body":"You can see you see a, you"},{"startTime":750.06,"endTime":753.51,"body":"can see a bunch of colors."},{"startTime":753.51,"endTime":756.69,"body":"What you don't see are those"},{"startTime":753.51,"endTime":756.69,"body":"bright reds at the surface."},{"startTime":756.69,"endTime":758.556,"body":"You can't see through the atmosphere."},{"startTime":758.556,"endTime":760.5,"body":"Angstrom was right, okay?"},{"startTime":760.5,"endTime":765.5,"body":"What you see is the"},{"startTime":760.5,"endTime":765.5,"body":"average color of the balls"},{"startTime":766.68,"endTime":770.58,"body":"that you can see, obviously enough, okay?"},{"startTime":770.58,"endTime":774.093,"body":"So you can only see some of"},{"startTime":770.58,"endTime":774.093,"body":"the way into the atmosphere,"},{"startTime":775.26,"endTime":779.16,"body":"and that determines, if we"},{"startTime":775.26,"endTime":779.16,"body":"sort of flip that around,"},{"startTime":779.16,"endTime":782.25,"body":"each of these balls"},{"startTime":779.16,"endTime":782.25,"body":"represents a temperature."},{"startTime":782.25,"endTime":784.17,"body":"They're all releasing energy."},{"startTime":784.17,"endTime":788.34,"body":"The hot ones are releasing"},{"startTime":784.17,"endTime":788.34,"body":"energy faster than the cold ones."},{"startTime":788.34,"endTime":791.82,"body":"So the average rate at which the Earth"},{"startTime":791.82,"endTime":794.61,"body":"is sending energy back out into space"},{"startTime":794.61,"endTime":797.22,"body":"is determined by the average temperature"},{"startTime":797.22,"endTime":801.99,"body":"or the average color of the"},{"startTime":797.22,"endTime":801.99,"body":"balls you can see from space."},{"startTime":801.99,"endTime":803.7,"body":"So far so good."},{"startTime":803.7,"endTime":805.65,"body":"Now, what's going to happen,"},{"startTime":805.65,"endTime":807.36,"body":"so there's the rate of"},{"startTime":805.65,"endTime":807.36,"body":"energy emitted to space"},{"startTime":807.36,"endTime":809.97,"body":"depends on the average"},{"startTime":807.36,"endTime":809.97,"body":"temperature of the molecules"},{"startTime":809.97,"endTime":811.743,"body":"that you can see from above."},{"startTime":812.67,"endTime":816.6,"body":"So as we increase CO2, what happens?"},{"startTime":816.6,"endTime":818.39,"body":"Well, I've just doubled the density"},{"startTime":818.39,"endTime":822.39,"body":"of CO2 molecules everywhere,"},{"startTime":822.39,"endTime":826.02,"body":"and I can't see as deep into my ball pit"},{"startTime":826.02,"endTime":827.643,"body":"because there's more CO2."},{"startTime":828.78,"endTime":831.93,"body":"So what that does is it forces energy"},{"startTime":831.93,"endTime":834.84,"body":"to escape from a higher altitude,"},{"startTime":834.84,"endTime":838.11,"body":"because, and you can see immediately,"},{"startTime":838.11,"endTime":840.03,"body":"it means that the molecules you can see"},{"startTime":840.03,"endTime":842.61,"body":"from space are colder,"},{"startTime":842.61,"endTime":844.713,"body":"so they're not releasing as much energy."},{"startTime":846.18,"endTime":850.92,"body":"So that mean higher air is colder,"},{"startTime":850.92,"endTime":854.7,"body":"and so it's radiating less"},{"startTime":850.92,"endTime":854.7,"body":"energy back out into space."},{"startTime":854.7,"endTime":858.78,"body":"So as we double CO2, we"},{"startTime":854.7,"endTime":858.78,"body":"reduce the amount of energy"},{"startTime":858.78,"endTime":860.7,"body":"going back out into space."},{"startTime":860.7,"endTime":864.663,"body":"The same energy in, less"},{"startTime":860.7,"endTime":864.663,"body":"energy out, global warming."},{"startTime":865.89,"endTime":870.89,"body":"This story has not mentioned"},{"startTime":865.89,"endTime":870.89,"body":"the amount of infrared light"},{"startTime":871.14,"endTime":873.39,"body":"going all the way through the atmosphere"},{"startTime":873.39,"endTime":876.897,"body":"in either direction, okay?"},{"startTime":876.897,"endTime":879.393,"body":"So Angstrom was wrong."},{"startTime":881.13,"endTime":882.33,"body":"You can ask at the end."},{"startTime":882.33,"endTime":884.52,"body":"If you haven't, well,"},{"startTime":882.33,"endTime":884.52,"body":"and you can either ask"},{"startTime":884.52,"endTime":888.843,"body":"or tell me at the end why"},{"startTime":884.52,"endTime":888.843,"body":"Angstrom's experiment was wrong,"},{"startTime":890.684,"endTime":891.84,"body":"So that's a little challenge to you"},{"startTime":891.84,"endTime":894.75,"body":"to think about through the rest of the..."},{"startTime":894.75,"endTime":898.23,"body":"So we have an imbalance."},{"startTime":898.23,"endTime":902.013,"body":"Same energy coming in,"},{"startTime":898.23,"endTime":902.013,"body":"less energy going out."},{"startTime":903.09,"endTime":905.64,"body":"The system has to warm up,"},{"startTime":905.64,"endTime":908.25,"body":"because energy is accumulating"},{"startTime":905.64,"endTime":908.25,"body":"in the climate system."},{"startTime":908.25,"endTime":910.38,"body":"How much it warms up,"},{"startTime":908.25,"endTime":910.38,"body":"we'll come on to that."},{"startTime":910.38,"endTime":911.883,"body":"But it has to warm up a bit."},{"startTime":912.72,"endTime":915.6,"body":"And here it is warming up,"},{"startTime":912.72,"endTime":915.6,"body":"to restore the balance,"},{"startTime":915.6,"endTime":918.603,"body":"to make it the same"},{"startTime":915.6,"endTime":918.603,"body":"color as it was before."},{"startTime":919.47,"endTime":921.483,"body":"So the whole atmosphere warms up."},{"startTime":922.53,"endTime":925.41,"body":"We've restored that color there"},{"startTime":925.41,"endTime":927.42,"body":"to what it was in the original states,"},{"startTime":927.42,"endTime":928.41,"body":"the average color."},{"startTime":928.41,"endTime":930.78,"body":"They're different balls,"},{"startTime":928.41,"endTime":930.78,"body":"different altitudes."},{"startTime":930.78,"endTime":932.94,"body":"You're not seeing as"},{"startTime":930.78,"endTime":932.94,"body":"deep into the atmosphere,"},{"startTime":932.94,"endTime":935.49,"body":"but you've warmed it all up,"},{"startTime":932.94,"endTime":935.49,"body":"so you're seeing on average"},{"startTime":935.49,"endTime":939.093,"body":"the same temperature"},{"startTime":935.49,"endTime":939.093,"body":"molecules as you saw before."},{"startTime":940.38,"endTime":943.11,"body":"And even better from the point of view"},{"startTime":943.11,"endTime":945.9,"body":"of explaining Arrhenius's observations,"},{"startTime":945.9,"endTime":948.3,"body":"if you double it again,"},{"startTime":948.3,"endTime":950.717,"body":"you actually get the same"},{"startTime":948.3,"endTime":950.717,"body":"reduction in temperature,"},{"startTime":950.717,"endTime":952.503,"body":"adding even more balls here."},{"startTime":953.34,"endTime":956.82,"body":"So we've explained two things"},{"startTime":953.34,"endTime":956.82,"body":"that Arrhenius posited."},{"startTime":956.82,"endTime":959.01,"body":"One was that increasing CO2"},{"startTime":959.01,"endTime":961.23,"body":"would increase global temperature"},{"startTime":961.23,"endTime":965.16,"body":"and also that every doubling of CO2,"},{"startTime":965.16,"endTime":967.71,"body":"even though it would take"},{"startTime":965.16,"endTime":967.71,"body":"twice as much extra CO2"},{"startTime":967.71,"endTime":971.31,"body":"in the atmosphere to"},{"startTime":967.71,"endTime":971.31,"body":"achieve that doubling,"},{"startTime":971.31,"endTime":974.25,"body":"every doubling would have"},{"startTime":971.31,"endTime":974.25,"body":"actually about the same impact"},{"startTime":974.25,"endTime":977.133,"body":"on the global energy"},{"startTime":974.25,"endTime":977.133,"body":"budget as the last one."},{"startTime":978.48,"endTime":982.113,"body":"If this has all seemed a"},{"startTime":978.48,"endTime":982.113,"body":"bit bemusing, don't panic."},{"startTime":983.07,"endTime":985.8,"body":"This is really well-understood science."},{"startTime":985.8,"endTime":987.385,"body":"I just wanted to stress this here"},{"startTime":987.385,"endTime":989.13,"body":"'cause I think it's quite"},{"startTime":987.385,"endTime":989.13,"body":"an interesting story"},{"startTime":989.13,"endTime":992.94,"body":"about how a very, Angstrom"},{"startTime":989.13,"endTime":992.94,"body":"was a Nobel Prize winner,"},{"startTime":992.94,"endTime":995.82,"body":"very eminent scientist could basically,"},{"startTime":995.82,"endTime":1000.29,"body":"he parked the whole"},{"startTime":995.82,"endTime":1000.29,"body":"CO2 theory for 50 years"},{"startTime":1000.29,"endTime":1003.48,"body":"with that elegant experiment"},{"startTime":1000.29,"endTime":1003.48,"body":"that just missed out"},{"startTime":1004.79,"endTime":1006.83,"body":"what was really crucial, okay,"},{"startTime":1006.83,"endTime":1008.03,"body":"I'll sort of give you a hint here,"},{"startTime":1008.03,"endTime":1010.16,"body":"what was really crucial for understanding"},{"startTime":1010.16,"endTime":1012.74,"body":"the greenhouse effect,"},{"startTime":1010.16,"endTime":1012.74,"body":"which is the interplay"},{"startTime":1012.74,"endTime":1016.343,"body":"between temperature and"},{"startTime":1012.74,"endTime":1016.343,"body":"density through the atmosphere."},{"startTime":1018.59,"endTime":1022.4,"body":"So, but even if you found this, you know,"},{"startTime":1022.4,"endTime":1025.4,"body":"a little bit confusing, you"},{"startTime":1022.4,"endTime":1025.4,"body":"don't need to worry about it"},{"startTime":1025.4,"endTime":1029.09,"body":"because we've actually seen the impact"},{"startTime":1029.09,"endTime":1032.63,"body":"of rising greenhouse gases from space."},{"startTime":1032.63,"endTime":1035.3,"body":"And this is an observation that I sort of,"},{"startTime":1035.3,"endTime":1036.68,"body":"it's a beautiful observation,"},{"startTime":1036.68,"endTime":1040.79,"body":"mostly because of the"},{"startTime":1036.68,"endTime":1040.79,"body":"ingenuity of the scientists"},{"startTime":1040.79,"endTime":1042.98,"body":"in the sort of late 1960s."},{"startTime":1042.98,"endTime":1047.423,"body":"They flew an infrared"},{"startTime":1042.98,"endTime":1047.423,"body":"spectrometer, which if you sort of,"},{"startTime":1048.56,"endTime":1051.14,"body":"that's a really delicate,"},{"startTime":1048.56,"endTime":1051.14,"body":"complicated instrument"},{"startTime":1051.14,"endTime":1056.06,"body":"that you would normally"},{"startTime":1051.14,"endTime":1056.06,"body":"require a lab to operate."},{"startTime":1056.06,"endTime":1060.62,"body":"And they flew an infrared"},{"startTime":1056.06,"endTime":1060.62,"body":"spectrometer on a spacecraft"},{"startTime":1060.62,"endTime":1064.25,"body":"in 1970, which is an"},{"startTime":1060.62,"endTime":1064.25,"body":"extraordinary achievement,"},{"startTime":1064.25,"endTime":1067.31,"body":"and they got a spectrum of infrared light."},{"startTime":1067.31,"endTime":1070.73,"body":"So that's a measure of"},{"startTime":1067.31,"endTime":1070.73,"body":"how much infrared light"},{"startTime":1070.73,"endTime":1073.883,"body":"was emerging depending on the color,"},{"startTime":1075.86,"endTime":1078.11,"body":"the color or the"},{"startTime":1075.86,"endTime":1078.11,"body":"wavelengths of the infrared."},{"startTime":1079.19,"endTime":1083.57,"body":"And then 25-odd years"},{"startTime":1079.19,"endTime":1083.57,"body":"later, 27 years later,"},{"startTime":1083.57,"endTime":1087.05,"body":"it so happens the Japanese space agency"},{"startTime":1087.05,"endTime":1089.48,"body":"flew a similar instrument."},{"startTime":1089.48,"endTime":1091.31,"body":"They didn't do it deliberately, just so,"},{"startTime":1091.31,"endTime":1094.91,"body":"but John Harries and his"},{"startTime":1091.31,"endTime":1094.91,"body":"coworkers, Helen Brindley,"},{"startTime":1094.91,"endTime":1097.28,"body":"noticed that it was the same observation"},{"startTime":1097.28,"endTime":1099.65,"body":"had been made separated by 27 years,"},{"startTime":1099.65,"endTime":1101.3,"body":"and it was separated also"},{"startTime":1101.3,"endTime":1104.86,"body":"by over 30 or 40 parts per"},{"startTime":1101.3,"endTime":1104.86,"body":"million of carbon dioxide."},{"startTime":1104.86,"endTime":1107.39,"body":"So carbon dioxide had"},{"startTime":1104.86,"endTime":1107.39,"body":"gone up in the interim"},{"startTime":1107.39,"endTime":1109.88,"body":"as had methane, CFCs, and so on."},{"startTime":1109.88,"endTime":1112.76,"body":"So they were able to"},{"startTime":1109.88,"endTime":1112.76,"body":"compare these two spectra,"},{"startTime":1112.76,"endTime":1114.11,"body":"correct it for the fact"},{"startTime":1112.76,"endTime":1114.11,"body":"that the temperature"},{"startTime":1114.11,"endTime":1116.84,"body":"was a bit different in the second period,"},{"startTime":1116.84,"endTime":1120.5,"body":"and see the reduction in outgoing energy"},{"startTime":1120.5,"endTime":1124.55,"body":"that resulted from the greenhouse"},{"startTime":1120.5,"endTime":1124.55,"body":"gases in the atmosphere."},{"startTime":1124.55,"endTime":1126.47,"body":"So it's not a theory."},{"startTime":1126.47,"endTime":1131.09,"body":"We can see the impact of"},{"startTime":1126.47,"endTime":1131.09,"body":"extra greenhouse gases"},{"startTime":1131.09,"endTime":1136.09,"body":"on outgoing energy in precisely"},{"startTime":1131.09,"endTime":1136.09,"body":"the wavelengths of light,"},{"startTime":1136.46,"endTime":1140.12,"body":"the color of infrared"},{"startTime":1136.46,"endTime":1140.12,"body":"light that we expect to see"},{"startTime":1140.12,"endTime":1141.52,"body":"because of our understanding"},{"startTime":1144.522,"endTime":1146.87,"body":"of the properties of these gases."},{"startTime":1146.87,"endTime":1150.77,"body":"So, you know, I've told you"},{"startTime":1146.87,"endTime":1150.77,"body":"sort of kind of how it works"},{"startTime":1150.77,"endTime":1153.95,"body":"and why we're very confident"},{"startTime":1150.77,"endTime":1153.95,"body":"in this part of the story"},{"startTime":1153.95,"endTime":1157.94,"body":"that as you increase carbon"},{"startTime":1153.95,"endTime":1157.94,"body":"dioxide concentrations,"},{"startTime":1157.94,"endTime":1161.3,"body":"it's trapping energy in the system."},{"startTime":1161.3,"endTime":1165.2,"body":"It's slowing down the rate at"},{"startTime":1161.3,"endTime":1165.2,"body":"which energy escapes to space,"},{"startTime":1165.2,"endTime":1168.65,"body":"creating an imbalance between"},{"startTime":1165.2,"endTime":1168.65,"body":"incoming energy from the sun"},{"startTime":1168.65,"endTime":1170.43,"body":"and outgoing energy to space"},{"startTime":1174.002,"endTime":1177.19,"body":"and thereby driving some global warming."},{"startTime":1178.7,"endTime":1181.85,"body":"I emphasize some because"},{"startTime":1178.7,"endTime":1181.85,"body":"we don't yet know,"},{"startTime":1181.85,"endTime":1184.73,"body":"so in from this explanation,"},{"startTime":1181.85,"endTime":1184.73,"body":"the scientific community"},{"startTime":1184.73,"endTime":1187.85,"body":"has made some progress on this,"},{"startTime":1184.73,"endTime":1187.85,"body":"but this explanation alone"},{"startTime":1187.85,"endTime":1191.78,"body":"doesn't tell you how much global warming."},{"startTime":1191.78,"endTime":1196.013,"body":"And to understand the"},{"startTime":1191.78,"endTime":1196.013,"body":"response, we need a model."},{"startTime":1197.69,"endTime":1201.987,"body":"And this headline really"},{"startTime":1197.69,"endTime":1201.987,"body":"annoyed me when I saw it."},{"startTime":1201.987,"endTime":1205.52,"body":"\"Yale 360,\" actually,"},{"startTime":1201.987,"endTime":1205.52,"body":"it's a great website."},{"startTime":1205.52,"endTime":1208.13,"body":"It's got loads of really"},{"startTime":1205.52,"endTime":1208.13,"body":"good information on it."},{"startTime":1208.13,"endTime":1211.49,"body":"But this article irritated me,"},{"startTime":1211.49,"endTime":1215.78,"body":"because you don't,"},{"startTime":1211.49,"endTime":1215.78,"body":"trusting a climate model,"},{"startTime":1215.78,"endTime":1218.06,"body":"you trust your priest or your partner."},{"startTime":1218.06,"endTime":1219.983,"body":"You don't trust a climate model."},{"startTime":1221.527,"endTime":1224.87,"body":"It's the wrong phrase to apply to a model."},{"startTime":1224.87,"endTime":1227.12,"body":"A model is a set of equations."},{"startTime":1227.12,"endTime":1230.09,"body":"It may require a computer to solve them,"},{"startTime":1230.09,"endTime":1232.34,"body":"but that's all it is."},{"startTime":1232.34,"endTime":1235.31,"body":"And it doesn't always even"},{"startTime":1232.34,"endTime":1235.31,"body":"need a computer to solve them."},{"startTime":1235.31,"endTime":1239.93,"body":"We can solve equations"},{"startTime":1235.31,"endTime":1239.93,"body":"using fluids and pipes."},{"startTime":1239.93,"endTime":1242.84,"body":"So I'm now going to introduce"},{"startTime":1239.93,"endTime":1242.84,"body":"you to a little model,"},{"startTime":1242.84,"endTime":1244.67,"body":"a climate model, which"},{"startTime":1242.84,"endTime":1244.67,"body":"we'll be seeing more of"},{"startTime":1244.67,"endTime":1245.99,"body":"during these lectures."},{"startTime":1245.99,"endTime":1250.99,"body":"And shall we cut to the"},{"startTime":1245.99,"endTime":1250.99,"body":"view of the demo now?"},{"startTime":1251.03,"endTime":1255.26,"body":"Thank you. Somebody's coming"},{"startTime":1251.03,"endTime":1255.26,"body":"over to help that out."},{"startTime":1255.26,"endTime":1257.48,"body":"So with apologies to the people at front"},{"startTime":1257.48,"endTime":1260.303,"body":"for the gentle whine,"},{"startTime":1261.372,"endTime":1264.08,"body":"but I shall step away from"},{"startTime":1261.372,"endTime":1264.08,"body":"it so that you don't get,"},{"startTime":1264.08,"endTime":1268.883,"body":"hopefully it doesn't pick up"},{"startTime":1264.08,"endTime":1268.883,"body":"too badly on the microphone."},{"startTime":1269.84,"endTime":1271.793,"body":"But what this represents,"},{"startTime":1272.75,"endTime":1277.25,"body":"this is a way of solving equations."},{"startTime":1277.25,"endTime":1281.66,"body":"It's a model, but it's"},{"startTime":1277.25,"endTime":1281.66,"body":"not using a computer."},{"startTime":1281.66,"endTime":1285.05,"body":"It's using, yes, it is using"},{"startTime":1281.66,"endTime":1285.05,"body":"a computer to drive it, okay?"},{"startTime":1285.05,"endTime":1288.83,"body":"But the actual, the"},{"startTime":1285.05,"endTime":1288.83,"body":"calculations themselves"},{"startTime":1288.83,"endTime":1293.03,"body":"are being done by the flow"},{"startTime":1288.83,"endTime":1293.03,"body":"of the fluid in the pipes,"},{"startTime":1293.03,"endTime":1296.6,"body":"because you've got a"},{"startTime":1293.03,"endTime":1296.6,"body":"better intuition probably"},{"startTime":1296.6,"endTime":1300.56,"body":"of how fluid flows through"},{"startTime":1296.6,"endTime":1300.56,"body":"pipes than you have"},{"startTime":1300.56,"endTime":1303.713,"body":"about how energy flows"},{"startTime":1300.56,"endTime":1303.713,"body":"through the global atmosphere."},{"startTime":1304.58,"endTime":1306.683,"body":"So we'll start at the top here."},{"startTime":1308.42,"endTime":1312.89,"body":"This is a sort of, this is a simulation"},{"startTime":1312.89,"endTime":1316.313,"body":"of our global climate system."},{"startTime":1317.21,"endTime":1321.713,"body":"The red stuff, which you can"},{"startTime":1317.21,"endTime":1321.713,"body":"see dripping in, is energy."},{"startTime":1322.58,"endTime":1325.55,"body":"And so the flow of energy coming in,"},{"startTime":1325.55,"endTime":1328.76,"body":"this is the energy"},{"startTime":1325.55,"endTime":1328.76,"body":"flowing in from the sun,"},{"startTime":1328.76,"endTime":1330.023,"body":"warming our planet."},{"startTime":1331.64,"endTime":1333.923,"body":"And down the bottom here,"},{"startTime":1333.923,"endTime":1336.65,"body":"(fluid bubbling)"},{"startTime":1333.923,"endTime":1336.65,"body":"(machine whirring)"},{"startTime":1336.65,"endTime":1338.21,"body":"yes, it's going down, not up,"},{"startTime":1338.21,"endTime":1341.0,"body":"but you know, we can't"},{"startTime":1338.21,"endTime":1341.0,"body":"have everything, okay?"},{"startTime":1341.0,"endTime":1343.673,"body":"This is energy flowing"},{"startTime":1341.0,"endTime":1343.673,"body":"back out into space."},{"startTime":1344.66,"endTime":1347.3,"body":"Can I ask you to ignore the cylinder"},{"startTime":1347.3,"endTime":1348.38,"body":"over on the right-hand side."},{"startTime":1348.38,"endTime":1349.28,"body":"We were discussing beforehand"},{"startTime":1349.28,"endTime":1350.78,"body":"whether to put some sort of drape,"},{"startTime":1350.78,"endTime":1353.99,"body":"some sort of cloth over it or something"},{"startTime":1353.99,"endTime":1355.76,"body":"for the big reveal in the next lecture."},{"startTime":1355.76,"endTime":1357.02,"body":"But we'll talk about the cylinder"},{"startTime":1357.02,"endTime":1357.853,"body":"over on the right-hand side."},{"startTime":1357.853,"endTime":1359.33,"body":"It's got a cork in it."},{"startTime":1357.853,"endTime":1359.33,"body":"It's not doing anything."},{"startTime":1359.33,"endTime":1361.58,"body":"Trust me, it's not doing anything, okay?"},{"startTime":1361.58,"endTime":1363.26,"body":"So just ignore it."},{"startTime":1363.26,"endTime":1366.2,"body":"So we have a balance between"},{"startTime":1363.26,"endTime":1366.2,"body":"energy coming in from the sun"},{"startTime":1366.2,"endTime":1371.2,"body":"and energy flowing out into"},{"startTime":1366.2,"endTime":1371.2,"body":"space, and this balance sets"},{"startTime":1375.44,"endTime":1376.74,"body":"the planetary temperature,"},{"startTime":1378.74,"endTime":1383.74,"body":"which is the level of fluid in this pipe."},{"startTime":1383.9,"endTime":1387.15,"body":"If we cranked up the power of the sun"},{"startTime":1388.52,"endTime":1391.97,"body":"and we had the same"},{"startTime":1388.52,"endTime":1391.97,"body":"processes controlling energy"},{"startTime":1391.97,"endTime":1393.98,"body":"going back out into space,"},{"startTime":1393.98,"endTime":1396.733,"body":"you can imagine the Earth's going"},{"startTime":1393.98,"endTime":1396.733,"body":"to have to get a lot warmer."},{"startTime":1398.3,"endTime":1401.6,"body":"I'm going to make one slight"},{"startTime":1398.3,"endTime":1401.6,"body":"modification of this model"},{"startTime":1401.6,"endTime":1404.33,"body":"in order to be able to sort"},{"startTime":1401.6,"endTime":1404.33,"body":"of do experiments with it,"},{"startTime":1404.33,"endTime":1409.33,"body":"which is that this natural flow,"},{"startTime":1404.33,"endTime":1409.33,"body":"which I'm showing you here,"},{"startTime":1409.88,"endTime":1414.62,"body":"is about 240 watts per square meter."},{"startTime":1414.62,"endTime":1417.26,"body":"That's two, you know, 240"},{"startTime":1414.62,"endTime":1417.26,"body":"watts every square meter"},{"startTime":1417.26,"endTime":1419.21,"body":"of the Earth's surface,"},{"startTime":1419.21,"endTime":1422.06,"body":"two old-fashioned incandescent light bulbs"},{"startTime":1422.06,"endTime":1426.353,"body":"beating down all the time,"},{"startTime":1422.06,"endTime":1426.353,"body":"flowing in, flowing out."},{"startTime":1427.25,"endTime":1430.16,"body":"Compare that to the kind of changes"},{"startTime":1430.16,"endTime":1432.023,"body":"that greenhouse gases have had."},{"startTime":1433.487,"endTime":1435.17,"body":"The greenhouse effect today"},{"startTime":1435.17,"endTime":1439.01,"body":"is about 2.5 to 3 watts per square meters,"},{"startTime":1439.01,"endTime":1442.793,"body":"so 1% or so of that natural flow."},{"startTime":1443.63,"endTime":1448.63,"body":"So I'd need a sort of fire"},{"startTime":1443.63,"endTime":1448.63,"body":"hose blowing in, okay,"},{"startTime":1449.39,"endTime":1452.75,"body":"to represent the full natural flow."},{"startTime":1452.75,"endTime":1457.75,"body":"And then, so I'm going to say,"},{"startTime":1452.75,"endTime":1457.75,"body":"well, most of it doesn't change."},{"startTime":1458.03,"endTime":1461.45,"body":"We're only going to focus"},{"startTime":1458.03,"endTime":1461.45,"body":"on the things that change."},{"startTime":1461.45,"endTime":1464.18,"body":"So I'm going to say"},{"startTime":1461.45,"endTime":1464.18,"body":"instead of the total energy"},{"startTime":1464.18,"endTime":1466.22,"body":"coming in from the sun,"},{"startTime":1466.22,"endTime":1471.123,"body":"I'm going to talk about the"},{"startTime":1466.22,"endTime":1471.123,"body":"net extra energy flow in,"},{"startTime":1472.7,"endTime":1475.82,"body":"and that could be driven"},{"startTime":1472.7,"endTime":1475.82,"body":"by two kinds of things."},{"startTime":1475.82,"endTime":1477.95,"body":"A little bit of an increase in"},{"startTime":1475.82,"endTime":1477.95,"body":"the power output of the sun,"},{"startTime":1477.95,"endTime":1481.16,"body":"for example, that would"},{"startTime":1477.95,"endTime":1481.16,"body":"increase the net energy flow in."},{"startTime":1481.16,"endTime":1484.13,"body":"But because it's the net energy flow in,"},{"startTime":1484.13,"endTime":1488.63,"body":"it could also be increased"},{"startTime":1484.13,"endTime":1488.63,"body":"by more greenhouse gases"},{"startTime":1488.63,"endTime":1491.39,"body":"reducing the energy flow out, yeah?"},{"startTime":1491.39,"endTime":1494.87,"body":"It has the same impact,"},{"startTime":1491.39,"endTime":1494.87,"body":"reduce energy flow out,"},{"startTime":1494.87,"endTime":1496.79,"body":"extra energy in, the net,"},{"startTime":1496.79,"endTime":1499.943,"body":"the impact on the net"},{"startTime":1496.79,"endTime":1499.943,"body":"energy flow in is the same."},{"startTime":1501.38,"endTime":1504.29,"body":"And so I also have to take that off"},{"startTime":1504.29,"endTime":1508.973,"body":"and say this is the net energy"},{"startTime":1504.29,"endTime":1508.973,"body":"flow back out into space."},{"startTime":1510.17,"endTime":1513.71,"body":"So this is the extra"},{"startTime":1510.17,"endTime":1513.71,"body":"energy I'm putting in,"},{"startTime":1513.71,"endTime":1517.64,"body":"extra energy when we're sort"},{"startTime":1513.71,"endTime":1517.64,"body":"of departing from equilibrium."},{"startTime":1517.64,"endTime":1520.97,"body":"And this, instead of being the"},{"startTime":1517.64,"endTime":1520.97,"body":"total planetary temperature,"},{"startTime":1520.97,"endTime":1522.92,"body":"sort of total temperature of the planet"},{"startTime":1523.79,"endTime":1528.79,"body":"is about 200 and, well,"},{"startTime":1523.79,"endTime":1528.79,"body":"it's about 300 degrees."},{"startTime":1528.95,"endTime":1531.29,"body":"You may think that sounds hot, doesn't it?"},{"startTime":1531.29,"endTime":1535.13,"body":"But that's in total energy"},{"startTime":1531.29,"endTime":1535.13,"body":"units, which are in Kelvin."},{"startTime":1535.13,"endTime":1537.08,"body":"And we can talk afterwards"},{"startTime":1535.13,"endTime":1537.08,"body":"about what that means"},{"startTime":1537.08,"endTime":1540.5,"body":"if you're interested, but I digress."},{"startTime":1540.5,"endTime":1543.92,"body":"So this is now, back"},{"startTime":1540.5,"endTime":1543.92,"body":"in sort of centigrade,"},{"startTime":1543.92,"endTime":1547.073,"body":"this is the change in"},{"startTime":1543.92,"endTime":1547.073,"body":"planetary temperature,"},{"startTime":1547.91,"endTime":1552.91,"body":"so changes from that"},{"startTime":1547.91,"endTime":1552.91,"body":"pre-industrial equilibrium state."},{"startTime":1553.37,"endTime":1556.07,"body":"So just to sort of, so"},{"startTime":1553.37,"endTime":1556.07,"body":"to avoid having to come"},{"startTime":1556.07,"endTime":1558.05,"body":"equipped with a fire hose,"},{"startTime":1558.05,"endTime":1561.08,"body":"we're showing you just small changes"},{"startTime":1561.08,"endTime":1562.94,"body":"about the background states,"},{"startTime":1562.94,"endTime":1565.46,"body":"well, small in the context of the planet,"},{"startTime":1565.46,"endTime":1567.68,"body":"energy flows through"},{"startTime":1565.46,"endTime":1567.68,"body":"the planet as a whole,"},{"startTime":1567.68,"endTime":1570.293,"body":"still substantial in terms"},{"startTime":1567.68,"endTime":1570.293,"body":"of impact on humanity."},{"startTime":1571.52,"endTime":1576.52,"body":"So what happens if we increase"},{"startTime":1571.52,"endTime":1576.52,"body":"the speed of the pump?"},{"startTime":1578.57,"endTime":1581.54,"body":"Well, I mean, intuitively, you know,"},{"startTime":1581.54,"endTime":1583.013,"body":"you know what's going to happen,"},{"startTime":1583.97,"endTime":1585.72,"body":"but I'm going to do it for you anyway."},{"startTime":1586.76,"endTime":1588.66,"body":"So I've doubled the speed of the pump."},{"startTime":1589.674,"endTime":1592.341,"body":"(pump whirring)"},{"startTime":1593.84,"endTime":1594.673,"body":"Mm-hmm."},{"startTime":1598.58,"endTime":1601.703,"body":"Is it all doing what you"},{"startTime":1598.58,"endTime":1601.703,"body":"expected it to do? I hope so."},{"startTime":1602.66,"endTime":1603.957,"body":"Actually. I quite often ask a class,"},{"startTime":1603.957,"endTime":1605.81,"body":"\"What do you think it's going to do?\""},{"startTime":1605.81,"endTime":1607.34,"body":"And people say, \"It's going to overflow.\""},{"startTime":1607.34,"endTime":1610.85,"body":"I say, \"Well, of course if I"},{"startTime":1607.34,"endTime":1610.85,"body":"overdid it, it would overflow.\""},{"startTime":1610.85,"endTime":1615.05,"body":"But it's stopped rising"},{"startTime":1610.85,"endTime":1615.05,"body":"now, hasn't it, yeah?"},{"startTime":1615.05,"endTime":1619.973,"body":"Because now the extra flow in from,"},{"startTime":1621.11,"endTime":1623.24,"body":"at the top is being balanced"},{"startTime":1623.24,"endTime":1624.86,"body":"by the extra flow being driven out"},{"startTime":1624.86,"endTime":1628.073,"body":"by the extra pressure in the pipe."},{"startTime":1629.15,"endTime":1634.05,"body":"And that corresponds to warmer"},{"startTime":1629.15,"endTime":1634.05,"body":"temperatures in the planet"},{"startTime":1635.12,"endTime":1637.37,"body":"forcing energy back out into space"},{"startTime":1637.37,"endTime":1639.053,"body":"faster than they did before."},{"startTime":1640.76,"endTime":1645.76,"body":"Now, if I do it again,"},{"startTime":1640.76,"endTime":1645.76,"body":"I'll increase the energy."},{"startTime":1646.16,"endTime":1647.69,"body":"I'll double the carbon dioxide again."},{"startTime":1647.69,"endTime":1652.683,"body":"So I'll increase the net energy"},{"startTime":1647.69,"endTime":1652.683,"body":"flow in, and here we are."},{"startTime":1652.683,"endTime":1655.35,"body":"(pump chugging)"},{"startTime":1658.13,"endTime":1663.13,"body":"So notice we get about"},{"startTime":1658.13,"endTime":1663.13,"body":"the same amount of warming"},{"startTime":1666.47,"endTime":1669.98,"body":"every extra energy flow,"},{"startTime":1669.98,"endTime":1674.54,"body":"every unit increase in the energy flow."},{"startTime":1674.54,"endTime":1676.4,"body":"Just as a warning, in"},{"startTime":1674.54,"endTime":1676.4,"body":"case you're disappointed"},{"startTime":1676.4,"endTime":1679.16,"body":"when you try this at home, it's really,"},{"startTime":1679.16,"endTime":1681.68,"body":"if I was to use water"},{"startTime":1679.16,"endTime":1681.68,"body":"for this, by the way,"},{"startTime":1681.68,"endTime":1683.18,"body":"I should've prefaced this with,"},{"startTime":1683.18,"endTime":1685.46,"body":"and apologies, guys, for"},{"startTime":1683.18,"endTime":1685.46,"body":"forgetting to mention this,"},{"startTime":1685.46,"endTime":1688.49,"body":"this brilliant contraption was built"},{"startTime":1688.49,"endTime":1691.46,"body":"by Benedict Pery of Oxford physics"},{"startTime":1691.46,"endTime":1694.4,"body":"and Toby Rowles of Durham physics,"},{"startTime":1694.4,"endTime":1698.06,"body":"and they had to think very"},{"startTime":1694.4,"endTime":1698.06,"body":"hard about designing it"},{"startTime":1698.06,"endTime":1700.22,"body":"to make sure it actually"},{"startTime":1698.06,"endTime":1700.22,"body":"did solve the equations"},{"startTime":1700.22,"endTime":1701.72,"body":"we wanted it to solve."},{"startTime":1701.72,"endTime":1703.13,"body":"And in fact, when I first"},{"startTime":1701.72,"endTime":1703.13,"body":"came up with the idea,"},{"startTime":1703.13,"endTime":1704.99,"body":"I thought, \"Well, we'll just use water.\""},{"startTime":1704.99,"endTime":1707.0,"body":"And if you try it at"},{"startTime":1704.99,"endTime":1707.0,"body":"home and just use water,"},{"startTime":1707.0,"endTime":1710.24,"body":"you won't find that, you know,"},{"startTime":1710.24,"endTime":1712.04,"body":"extra, double the speed of the pump"},{"startTime":1712.04,"endTime":1715.37,"body":"you get twice as high"},{"startTime":1712.04,"endTime":1715.37,"body":"because water goes turbulent,"},{"startTime":1715.37,"endTime":1718.58,"body":"and turbulence is a"},{"startTime":1715.37,"endTime":1718.58,"body":"mess, turbulence is hard."},{"startTime":1718.58,"endTime":1720.77,"body":"So this fluid, so if you use olive oil"},{"startTime":1720.77,"endTime":1722.17,"body":"or something like that,"},{"startTime":1720.77,"endTime":1722.17,"body":"it'll be fine, okay?"},{"startTime":1722.17,"endTime":1723.41,"body":"So it's a little bit viscous."},{"startTime":1723.41,"endTime":1725.81,"body":"So the fluid we're using"},{"startTime":1723.41,"endTime":1725.81,"body":"here is a little bit viscous,"},{"startTime":1725.81,"endTime":1728.15,"body":"stops it going turbulent,"},{"startTime":1725.81,"endTime":1728.15,"body":"stops it getting difficult."},{"startTime":1728.15,"endTime":1730.67,"body":"As soon as it goes turbulent,"},{"startTime":1728.15,"endTime":1730.67,"body":"life gets difficult."},{"startTime":1730.67,"endTime":1733.55,"body":"That's a general rule of fluid mechanics."},{"startTime":1733.55,"endTime":1736.88,"body":"Right, so we've captured the idea"},{"startTime":1736.88,"endTime":1741.88,"body":"that as you increase the net"},{"startTime":1736.88,"endTime":1741.88,"body":"energy into the climate system"},{"startTime":1742.67,"endTime":1744.713,"body":"by increasing greenhouse gases,"},{"startTime":1745.76,"endTime":1750.76,"body":"you require the Earth's"},{"startTime":1745.76,"endTime":1750.76,"body":"surface temperature to increase"},{"startTime":1751.67,"endTime":1754.16,"body":"in order to drive that energy out again"},{"startTime":1754.16,"endTime":1757.973,"body":"to restore the balance between"},{"startTime":1754.16,"endTime":1757.973,"body":"incoming and outgoing energy."},{"startTime":1759.26,"endTime":1760.253,"body":"So far so good."},{"startTime":1761.15,"endTime":1764.843,"body":"But with this system,"},{"startTime":1761.15,"endTime":1764.843,"body":"we were able to do a,"},{"startTime":1767.87,"endTime":1772.37,"body":"we were able to do a little test to,"},{"startTime":1772.37,"endTime":1774.443,"body":"if I just restore it to its original,"},{"startTime":1775.43,"endTime":1777.74,"body":"we were able to do a"},{"startTime":1775.43,"endTime":1777.74,"body":"little test of, you know,"},{"startTime":1777.74,"endTime":1780.56,"body":"we raised the pump level a little bit,"},{"startTime":1780.56,"endTime":1782.81,"body":"and then we knew how much, and"},{"startTime":1780.56,"endTime":1782.81,"body":"then we were able to predict"},{"startTime":1782.81,"endTime":1787.07,"body":"how much we'd need to"},{"startTime":1782.81,"endTime":1787.07,"body":"raise the pump level again"},{"startTime":1787.07,"endTime":1789.95,"body":"in order to go, in order to raise it,"},{"startTime":1789.95,"endTime":1793.07,"body":"how much it would raise the water level,"},{"startTime":1793.07,"endTime":1794.903,"body":"the fluid level the second time."},{"startTime":1796.49,"endTime":1800.51,"body":"Interestingly, when"},{"startTime":1796.49,"endTime":1800.51,"body":"scientists were first thinking"},{"startTime":1800.51,"endTime":1804.053,"body":"about the climate problem, they"},{"startTime":1800.51,"endTime":1804.053,"body":"were more in this situation."},{"startTime":1805.16,"endTime":1807.35,"body":"They could see it was fluctuating."},{"startTime":1807.35,"endTime":1809.75,"body":"They could see how it worked."},{"startTime":1809.75,"endTime":1812.03,"body":"But they hadn't actually turned,"},{"startTime":1812.03,"endTime":1816.503,"body":"well, we humanity hadn't"},{"startTime":1812.03,"endTime":1816.503,"body":"actually dialed up the knob yet."},{"startTime":1819.571,"endTime":1820.61,"body":"So if you had to do that,"},{"startTime":1820.61,"endTime":1822.743,"body":"now with this simple system, you know,"},{"startTime":1823.97,"endTime":1826.1,"body":"we understand fluid flowing"},{"startTime":1823.97,"endTime":1826.1,"body":"in pipes pretty well."},{"startTime":1826.1,"endTime":1827.9,"body":"If you knew the viscosity of the fluid,"},{"startTime":1827.9,"endTime":1830.09,"body":"if you knew the diameter"},{"startTime":1827.9,"endTime":1830.09,"body":"of that pipe and so on,"},{"startTime":1830.09,"endTime":1833.0,"body":"you'd be able to predict"},{"startTime":1830.09,"endTime":1833.0,"body":"what would happen."},{"startTime":1833.0,"endTime":1834.74,"body":"But of course with the climate system,"},{"startTime":1834.74,"endTime":1837.17,"body":"there's a lot of processes involved."},{"startTime":1837.17,"endTime":1840.38,"body":"So how can we predict before it happens?"},{"startTime":1840.38,"endTime":1841.82,"body":"You know, once we've done it once,"},{"startTime":1841.82,"endTime":1843.134,"body":"we could predict what would happen"},{"startTime":1843.134,"endTime":1845.42,"body":"if we did it again, no problem."},{"startTime":1845.42,"endTime":1849.65,"body":"But how could we predict"},{"startTime":1845.42,"endTime":1849.65,"body":"how much that would go up"},{"startTime":1849.65,"endTime":1851.24,"body":"when we're in this situation"},{"startTime":1851.24,"endTime":1852.94,"body":"before anything's happened at all?"},{"startTime":1854.12,"endTime":1856.82,"body":"And that comes back to the modeling."},{"startTime":1856.82,"endTime":1859.88,"body":"So I think I'll go back"},{"startTime":1856.82,"endTime":1859.88,"body":"to the PowerPoint now."},{"startTime":1859.88,"endTime":1861.89,"body":"So that'll switch off the annoying noise."},{"startTime":1861.89,"endTime":1866.45,"body":"So remember this, and"},{"startTime":1861.89,"endTime":1866.45,"body":"say a little thank you"},{"startTime":1866.45,"endTime":1869.51,"body":"to Toby Rowles and Ben Pery"},{"startTime":1866.45,"endTime":1869.51,"body":"for their amazing craftsmanship"},{"startTime":1869.51,"endTime":1871.91,"body":"that it actually worked on the day."},{"startTime":1871.91,"endTime":1874.013,"body":"And we will now switch it off."},{"startTime":1875.06,"endTime":1876.56,"body":"But you'll see plenty more of it."},{"startTime":1876.56,"endTime":1878.33,"body":"And if you're wondering what's this"},{"startTime":1878.33,"endTime":1879.98,"body":"and why has it got a cork in it,"},{"startTime":1879.98,"endTime":1882.26,"body":"all will be revealed"},{"startTime":1879.98,"endTime":1882.26,"body":"in the ocean's lecture,"},{"startTime":1882.26,"endTime":1885.143,"body":"yes, that's a hint, in January."},{"startTime":1886.25,"endTime":1889.73,"body":"So you don't need to trust climate models."},{"startTime":1889.73,"endTime":1892.913,"body":"This is a model. It's a plastic tube."},{"startTime":1894.2,"endTime":1898.613,"body":"F is the extra flow we're putting in,"},{"startTime":1900.32,"endTime":1903.35,"body":"h is the increased water depth,"},{"startTime":1903.35,"endTime":1907.25,"body":"k is the openness of the outlet pipe,"},{"startTime":1907.25,"endTime":1909.08,"body":"the sort of willingness of the outlet pipe"},{"startTime":1909.08,"endTime":1910.85,"body":"to let fluid through it,"},{"startTime":1910.85,"endTime":1912.98,"body":"which of course depends on"},{"startTime":1910.85,"endTime":1912.98,"body":"the syrupiness of the fluid"},{"startTime":1912.98,"endTime":1914.84,"body":"you're putting in and so on."},{"startTime":1914.84,"endTime":1917.39,"body":"And we put these things together,"},{"startTime":1917.39,"endTime":1919.58,"body":"and it's sort of fairly obvious, isn't it?"},{"startTime":1919.58,"endTime":1923.72,"body":"The faster, the bigger"},{"startTime":1919.58,"endTime":1923.72,"body":"the F, the higher the h,"},{"startTime":1923.72,"endTime":1928.72,"body":"the more the fluid level"},{"startTime":1923.72,"endTime":1928.72,"body":"in the pipe will raise."},{"startTime":1929.45,"endTime":1931.043,"body":"So that's a model."},{"startTime":1932.06,"endTime":1932.893,"body":"This is a model,"},{"startTime":1933.98,"endTime":1936.83,"body":"the Earth's climate system in equilibrium."},{"startTime":1936.83,"endTime":1939.083,"body":"Notice it's really very similar."},{"startTime":1940.79,"endTime":1941.89,"body":"And this is the point."},{"startTime":1943.01,"endTime":1948.01,"body":"This system of fluid in pipes"},{"startTime":1943.01,"endTime":1948.01,"body":"is solving the same equations."},{"startTime":1949.76,"endTime":1952.82,"body":"Equations are not things"},{"startTime":1949.76,"endTime":1952.82,"body":"that mathematicians dream up"},{"startTime":1952.82,"endTime":1955.13,"body":"to annoy people at school,"},{"startTime":1955.13,"endTime":1958.103,"body":"although many people feel that's the case."},{"startTime":1959.15,"endTime":1963.92,"body":"They're actually what nature"},{"startTime":1959.15,"endTime":1963.92,"body":"uses to govern our universe."},{"startTime":1963.92,"endTime":1968.92,"body":"And this is the equation, or"},{"startTime":1963.92,"endTime":1968.92,"body":"approximately the equation,"},{"startTime":1968.96,"endTime":1972.593,"body":"that governs our climate"},{"startTime":1968.96,"endTime":1972.593,"body":"system in equilibrium."},{"startTime":1974.12,"endTime":1978.2,"body":"F now is that net additional energy"},{"startTime":1978.2,"endTime":1980.39,"body":"flowing into the climate system,"},{"startTime":1980.39,"endTime":1982.61,"body":"which might be due to a"},{"startTime":1980.39,"endTime":1982.61,"body":"dialing up of the power"},{"startTime":1982.61,"endTime":1984.17,"body":"out of the sun on the one hand"},{"startTime":1984.17,"endTime":1986.78,"body":"or a dialing up of greenhouse gas levels"},{"startTime":1986.78,"endTime":1989.57,"body":"throttling outgoing energy to space,"},{"startTime":1989.57,"endTime":1994.19,"body":"both of which cause a net"},{"startTime":1989.57,"endTime":1994.19,"body":"energy into the climate system."},{"startTime":1994.19,"endTime":1996.893,"body":"So less energy out is the"},{"startTime":1994.19,"endTime":1996.893,"body":"same as more energy in."},{"startTime":1998.57,"endTime":2001.03,"body":"T, big capital T, always refers"},{"startTime":2001.03,"endTime":2002.14,"body":"to global average temperature,"},{"startTime":2002.14,"endTime":2005.05,"body":"but now it refers to the increase"},{"startTime":2005.05,"endTime":2007.96,"body":"in global average temperature"},{"startTime":2005.05,"endTime":2007.96,"body":"above pre-industrial,"},{"startTime":2007.96,"endTime":2009.64,"body":"so not an absolute temperature"},{"startTime":2009.64,"endTime":2012.19,"body":"but a change in temperature"},{"startTime":2009.64,"endTime":2012.19,"body":"above pre-industrial,"},{"startTime":2012.19,"endTime":2015.07,"body":"what people refer to as the"},{"startTime":2012.19,"endTime":2015.07,"body":"level of global warming."},{"startTime":2015.07,"endTime":2018.133,"body":"And lambda here is the"},{"startTime":2015.07,"endTime":2018.133,"body":"sensitivity parameter."},{"startTime":2020.05,"endTime":2024.55,"body":"It's like k, it's something"},{"startTime":2020.05,"endTime":2024.55,"body":"that it's quite hard"},{"startTime":2024.55,"endTime":2025.81,"body":"to go out and measure."},{"startTime":2025.81,"endTime":2028.51,"body":"It's just what determines the relationship"},{"startTime":2028.51,"endTime":2033.51,"body":"between F and between the"},{"startTime":2028.51,"endTime":2033.51,"body":"forcing, well, F, the forcing,"},{"startTime":2033.67,"endTime":2035.323,"body":"and T, the temperature."},{"startTime":2037.24,"endTime":2039.25,"body":"A very important quantity"},{"startTime":2039.25,"endTime":2041.14,"body":"that people talked about for years,"},{"startTime":2041.14,"endTime":2042.37,"body":"and remember I said at the"},{"startTime":2041.14,"endTime":2042.37,"body":"beginning of the lecture"},{"startTime":2042.37,"endTime":2044.95,"body":"I was going to talk about"},{"startTime":2042.37,"endTime":2044.95,"body":"scientific cul-de-sacs"},{"startTime":2044.95,"endTime":2047.86,"body":"a little bit in this lecture,"},{"startTime":2047.86,"endTime":2052.84,"body":"and my personal view is our focus,"},{"startTime":2052.84,"endTime":2054.7,"body":"the climate science community's focus"},{"startTime":2054.7,"endTime":2056.98,"body":"on the equilibrium climate sensitivity"},{"startTime":2056.98,"endTime":2059.2,"body":"was a bit of a cul-de-sac."},{"startTime":2059.2,"endTime":2063.34,"body":"But when we started thinking"},{"startTime":2059.2,"endTime":2063.34,"body":"about the climate problem,"},{"startTime":2063.34,"endTime":2065.59,"body":"this is the way we thought about it."},{"startTime":2065.59,"endTime":2069.28,"body":"We knew that as you"},{"startTime":2065.59,"endTime":2069.28,"body":"increase the flow of energy"},{"startTime":2069.28,"endTime":2072.34,"body":"into the climate system,"},{"startTime":2069.28,"endTime":2072.34,"body":"temperatures would have to respond."},{"startTime":2072.34,"endTime":2074.32,"body":"And we asked, \"Well, how much warming"},{"startTime":2074.32,"endTime":2077.86,"body":"would we need to restore the balance"},{"startTime":2077.86,"endTime":2080.98,"body":"between incoming and outgoing energy?\""},{"startTime":2080.98,"endTime":2083.08,"body":"Very simple question to ask."},{"startTime":2083.08,"endTime":2087.58,"body":"And in particular, people"},{"startTime":2083.08,"endTime":2087.58,"body":"asked this specific question,"},{"startTime":2087.58,"endTime":2091.27,"body":"if we were to double carbon"},{"startTime":2087.58,"endTime":2091.27,"body":"dioxide concentrations,"},{"startTime":2091.27,"endTime":2095.89,"body":"how much warming would we"},{"startTime":2091.27,"endTime":2095.89,"body":"need to restore the balance"},{"startTime":2095.89,"endTime":2097.81,"body":"between incoming and outgoing energy?"},{"startTime":2097.81,"endTime":2101.893,"body":"That's what's called the"},{"startTime":2097.81,"endTime":2101.893,"body":"equilibrium climate sensitivity,"},{"startTime":2103.15,"endTime":2104.59,"body":"and it's exactly the same equation."},{"startTime":2104.59,"endTime":2107.47,"body":"I've just sort of added"},{"startTime":2104.59,"endTime":2107.47,"body":"these little suffixes here"},{"startTime":2107.47,"endTime":2109.75,"body":"to say this is the special case"},{"startTime":2109.75,"endTime":2114.31,"body":"where you haven't just done any"},{"startTime":2109.75,"endTime":2114.31,"body":"old extra flow of energy in,"},{"startTime":2114.31,"endTime":2117.34,"body":"but you've specifically"},{"startTime":2114.31,"endTime":2117.34,"body":"doubled carbon dioxide."},{"startTime":2117.34,"endTime":2120.16,"body":"So it's a sort of a standard experiment"},{"startTime":2120.16,"endTime":2122.14,"body":"that people might think of doing, either,"},{"startTime":2122.14,"endTime":2124.03,"body":"well, you can do it with a climate model."},{"startTime":2124.03,"endTime":2126.313,"body":"We can't actually do"},{"startTime":2124.03,"endTime":2126.313,"body":"it with the real world."},{"startTime":2127.3,"endTime":2128.5,"body":"Well, we're sort of in the process"},{"startTime":2128.5,"endTime":2131.02,"body":"of doing something like"},{"startTime":2128.5,"endTime":2131.02,"body":"it with the real world,"},{"startTime":2131.02,"endTime":2135.1,"body":"but we aren't in a position"},{"startTime":2131.02,"endTime":2135.1,"body":"with the real world crucially"},{"startTime":2135.1,"endTime":2136.84,"body":"to do what we can do with a climate model,"},{"startTime":2136.84,"endTime":2138.16,"body":"which is to double carbon dioxide"},{"startTime":2138.16,"endTime":2140.773,"body":"and then leave it indefinitely"},{"startTime":2138.16,"endTime":2140.773,"body":"to see what it does."},{"startTime":2141.82,"endTime":2142.837,"body":"I mean, I suppose we"},{"startTime":2141.82,"endTime":2142.837,"body":"could leave the world."},{"startTime":2142.837,"endTime":2146.86,"body":"No, okay, nevermind, we'll get"},{"startTime":2142.837,"endTime":2146.86,"body":"lost in the philosophy that,"},{"startTime":2146.86,"endTime":2148.03,"body":"but anyway, and again,"},{"startTime":2148.03,"endTime":2150.37,"body":"lambda here is the"},{"startTime":2148.03,"endTime":2150.37,"body":"sensitivity parameter again,"},{"startTime":2150.37,"endTime":2155.26,"body":"and lambda depends on lots of"},{"startTime":2150.37,"endTime":2155.26,"body":"very uncertain processes in,"},{"startTime":2155.26,"endTime":2157.45,"body":"it depends on water"},{"startTime":2155.26,"endTime":2157.45,"body":"vapor in the atmosphere."},{"startTime":2157.45,"endTime":2158.68,"body":"It depends on clouds."},{"startTime":2158.68,"endTime":2163.68,"body":"It depends on melting of snow,"},{"startTime":2158.68,"endTime":2163.68,"body":"how fast sea ice retreats,"},{"startTime":2164.14,"endTime":2166.81,"body":"how the rate of temperature change"},{"startTime":2166.81,"endTime":2169.12,"body":"through the atmosphere adjusts and so on."},{"startTime":2169.12,"endTime":2170.71,"body":"I could spend a whole lecture"},{"startTime":2170.71,"endTime":2172.723,"body":"talking about what determines lambda,"},{"startTime":2173.68,"endTime":2176.8,"body":"but all you really need to"},{"startTime":2173.68,"endTime":2176.8,"body":"know is the various things"},{"startTime":2176.8,"endTime":2180.16,"body":"that determine lambda"},{"startTime":2176.8,"endTime":2180.16,"body":"are, (coughs) excuse me,"},{"startTime":2180.16,"endTime":2182.47,"body":"are uncertain, so it's uncertain."},{"startTime":2182.47,"endTime":2184.573,"body":"It's something we're not sure what it is."},{"startTime":2185.77,"endTime":2188.323,"body":"And back in 1979,"},{"startTime":2189.46,"endTime":2193.0,"body":"Jules Charney chaired a board,"},{"startTime":2193.0,"endTime":2195.4,"body":"a panel of the National"},{"startTime":2193.0,"endTime":2195.4,"body":"Academy of Sciences"},{"startTime":2195.4,"endTime":2198.7,"body":"in the US that estimated a range"},{"startTime":2198.7,"endTime":2201.25,"body":"for this climate sensitivity parameter."},{"startTime":2201.25,"endTime":2203.98,"body":"This is the thing which Svante Arrhenius"},{"startTime":2203.98,"endTime":2206.173,"body":"said it was about four degrees, remember?"},{"startTime":2207.25,"endTime":2211.36,"body":"Well, these guys, they looked"},{"startTime":2207.25,"endTime":2211.36,"body":"at Arrhenius's reasoning,"},{"startTime":2211.36,"endTime":2213.97,"body":"and they thought that that was"},{"startTime":2211.36,"endTime":2213.97,"body":"probably a bit over the top."},{"startTime":2213.97,"endTime":2218.23,"body":"They actually, well, they"},{"startTime":2213.97,"endTime":2218.23,"body":"didn't really have much,"},{"startTime":2218.23,"endTime":2220.0,"body":"that much quantitative support to it."},{"startTime":2220.0,"endTime":2223.78,"body":"What they had was a couple now"},{"startTime":2223.78,"endTime":2228.78,"body":"of actual numerical simulations"},{"startTime":2223.78,"endTime":2228.78,"body":"of the Earth's climate"},{"startTime":2229.84,"endTime":2232.21,"body":"in which they could double carbon dioxide."},{"startTime":2232.21,"endTime":2233.77,"body":"So they're in the sort"},{"startTime":2232.21,"endTime":2233.77,"body":"of position we were in."},{"startTime":2233.77,"endTime":2236.35,"body":"I'm not going to switch it on"},{"startTime":2233.77,"endTime":2236.35,"body":"again, 'cause annoying noise,"},{"startTime":2236.35,"endTime":2238.27,"body":"but they were in the position we were in"},{"startTime":2238.27,"endTime":2240.37,"body":"where they hadn't actually done anything"},{"startTime":2240.37,"endTime":2243.34,"body":"to the system itself, and it"},{"startTime":2240.37,"endTime":2243.34,"body":"was sort of wobbling about,"},{"startTime":2243.34,"endTime":2246.28,"body":"but they were using computer simulations"},{"startTime":2246.28,"endTime":2247.96,"body":"of the Earth's climate to try and work out"},{"startTime":2247.96,"endTime":2251.98,"body":"what might happen if we were"},{"startTime":2247.96,"endTime":2251.98,"body":"to double carbon dioxide,"},{"startTime":2251.98,"endTime":2253.87,"body":"and they came up with this range."},{"startTime":2253.87,"endTime":2255.37,"body":"And it's important to recognize"},{"startTime":2255.37,"endTime":2258.34,"body":"this was an entirely"},{"startTime":2255.37,"endTime":2258.34,"body":"model-based prediction."},{"startTime":2258.34,"endTime":2261.73,"body":"The blue there shows, you know,"},{"startTime":2261.73,"endTime":2264.64,"body":"these are monthly temperatures since 1850."},{"startTime":2264.64,"endTime":2268.0,"body":"This is the modern record, so it's,"},{"startTime":2268.0,"endTime":2270.49,"body":"I don't know exactly"},{"startTime":2268.0,"endTime":2270.49,"body":"what the record was like"},{"startTime":2270.49,"endTime":2272.8,"body":"when Jules Charney was looking at it,"},{"startTime":2272.8,"endTime":2274.24,"body":"but the important point was, you know,"},{"startTime":2274.24,"endTime":2276.04,"body":"it wouldn't have been better than this,"},{"startTime":2276.04,"endTime":2277.9,"body":"because it was, we're"},{"startTime":2276.04,"endTime":2277.9,"body":"talking 40 years ago."},{"startTime":2277.9,"endTime":2281.397,"body":"So, you know, there"},{"startTime":2277.9,"endTime":2281.397,"body":"was no way they hadn't,"},{"startTime":2283.42,"endTime":2286.022,"body":"they weren't observing a"},{"startTime":2283.42,"endTime":2286.022,"body":"global warming at the time."},{"startTime":2286.022,"endTime":2288.872,"body":"In fact, if anything, temperatures"},{"startTime":2286.022,"endTime":2288.872,"body":"had been pretty stable"},{"startTime":2290.11,"endTime":2292.093,"body":"for the past 20 or 30 years."},{"startTime":2293.38,"endTime":2295.442,"body":"There is a sort of myth out there"},{"startTime":2295.442,"endTime":2296.32,"body":"that the scientific community"},{"startTime":2296.32,"endTime":2298.663,"body":"was predicting a global"},{"startTime":2296.32,"endTime":2298.663,"body":"ice age in the '70s."},{"startTime":2299.62,"endTime":2301.904,"body":"It's very hard to find"},{"startTime":2299.62,"endTime":2301.904,"body":"the foundation for this."},{"startTime":2301.904,"endTime":2302.83,"body":"I mean, there were, you know,"},{"startTime":2302.83,"endTime":2305.02,"body":"every time the weather"},{"startTime":2302.83,"endTime":2305.02,"body":"got cold in the 1970s,"},{"startTime":2305.02,"endTime":2306.64,"body":"a newspaper ran an article"},{"startTime":2306.64,"endTime":2307.9,"body":"saying we're going to get a new ice age."},{"startTime":2307.9,"endTime":2310.75,"body":"But that's just 'cause that's"},{"startTime":2307.9,"endTime":2310.75,"body":"what newspapers like to do."},{"startTime":2311.98,"endTime":2315.04,"body":"It's very hard to find"},{"startTime":2311.98,"endTime":2315.04,"body":"actual scientific articles"},{"startTime":2315.04,"endTime":2316.79,"body":"predicting a new ice age back then."},{"startTime":2318.19,"endTime":2321.1,"body":"But what was very clear to"},{"startTime":2318.19,"endTime":2321.1,"body":"the scientific community"},{"startTime":2321.1,"endTime":2324.46,"body":"was they knew what was"},{"startTime":2321.1,"endTime":2324.46,"body":"happening to carbon dioxide,"},{"startTime":2324.46,"endTime":2328.823,"body":"and they predicted that"},{"startTime":2324.46,"endTime":2328.823,"body":"a likely outcome of that"},{"startTime":2328.823,"endTime":2331.0,"body":"would be a global warming."},{"startTime":2331.0,"endTime":2335.66,"body":"I actually remember when I"},{"startTime":2331.0,"endTime":2335.66,"body":"was a graduate student in,"},{"startTime":2337.438,"endTime":2338.98,"body":"I mean, you know, so I"},{"startTime":2337.438,"endTime":2338.98,"body":"was a graduate student"},{"startTime":2338.98,"endTime":2342.19,"body":"sort of around here, and I remember a,"},{"startTime":2342.19,"endTime":2344.5,"body":"one of the first lectures I went to,"},{"startTime":2344.5,"endTime":2347.8,"body":"a very eminent professor in Oxford"},{"startTime":2347.8,"endTime":2351.16,"body":"was sort of chatting about this record."},{"startTime":2351.16,"endTime":2352.9,"body":"And I remember him saying,"},{"startTime":2351.16,"endTime":2352.9,"body":"\"Yeah, it's interesting,"},{"startTime":2352.9,"endTime":2355.24,"body":"isn't it, how they always"},{"startTime":2352.9,"endTime":2355.24,"body":"predict the warming"},{"startTime":2355.24,"endTime":2357.103,"body":"right after the end of the data\""},{"startTime":2358.57,"endTime":2360.047,"body":"in a sort of slightly sort of,"},{"startTime":2360.047,"endTime":2362.56,"body":"\"Ah, we're cleverer than"},{"startTime":2360.047,"endTime":2362.56,"body":"that\" sort of tone of voice."},{"startTime":2362.56,"endTime":2365.383,"body":"Anyway, obviously were no"},{"startTime":2362.56,"endTime":2365.383,"body":"longer in that situation,"},{"startTime":2367.083,"endTime":2369.46,"body":"but it wasn't, you know,"},{"startTime":2367.083,"endTime":2369.46,"body":"back then global warming"},{"startTime":2369.46,"endTime":2371.053,"body":"was something that, you know,"},{"startTime":2373.0,"endTime":2374.92,"body":"attention-seekers and geographers did,"},{"startTime":2374.92,"endTime":2376.99,"body":"whereas, you know, hardcore physicists"},{"startTime":2376.99,"endTime":2380.53,"body":"did weather and, you know, El Nino"},{"startTime":2380.53,"endTime":2382.33,"body":"and sort of interesting"},{"startTime":2380.53,"endTime":2382.33,"body":"climate variability"},{"startTime":2382.33,"endTime":2384.289,"body":"and that sort of thing."},{"startTime":2384.289,"endTime":2385.75,"body":"But that, of course, has changed."},{"startTime":2385.75,"endTime":2389.68,"body":"But you know, back then,"},{"startTime":2385.75,"endTime":2389.68,"body":"the likes of Charney"},{"startTime":2389.68,"endTime":2393.279,"body":"were in a position"},{"startTime":2389.68,"endTime":2393.279,"body":"where, as we were there,"},{"startTime":2393.279,"endTime":2395.41,"body":"that if they were going to make"},{"startTime":2393.279,"endTime":2395.41,"body":"a prediction of global warming,"},{"startTime":2395.41,"endTime":2398.5,"body":"it had to be model based"},{"startTime":2395.41,"endTime":2398.5,"body":"because they weren't,"},{"startTime":2398.5,"endTime":2400.81,"body":"they didn't have any data to help them."},{"startTime":2400.81,"endTime":2402.46,"body":"And they just had two models,"},{"startTime":2402.46,"endTime":2405.43,"body":"and basically the 1.5"},{"startTime":2402.46,"endTime":2405.43,"body":"to 4.5 range they gave"},{"startTime":2405.43,"endTime":2408.43,"body":"was based on the fact that"},{"startTime":2405.43,"endTime":2408.43,"body":"the two models they had,"},{"startTime":2408.43,"endTime":2410.59,"body":"one of them had a climate"},{"startTime":2408.43,"endTime":2410.59,"body":"sensitivity of two,"},{"startTime":2410.59,"endTime":2412.66,"body":"the other one had a climate"},{"startTime":2410.59,"endTime":2412.66,"body":"sensitivity of four."},{"startTime":2412.66,"endTime":2413.53,"body":"They thought, \"Well, it's a bit silly"},{"startTime":2413.53,"endTime":2414.37,"body":"just to give the range,"},{"startTime":2414.37,"endTime":2416.05,"body":"so we'll add half a degree on either end.\""},{"startTime":2416.05,"endTime":2419.23,"body":"I believe, I talked to"},{"startTime":2416.05,"endTime":2419.23,"body":"Carl Wunsch about it,"},{"startTime":2419.23,"endTime":2421.09,"body":"that was kind of the level it was at."},{"startTime":2421.09,"endTime":2422.14,"body":"That was what, you know."},{"startTime":2422.14,"endTime":2424.48,"body":"So can we do better than that?"},{"startTime":2424.48,"endTime":2427.963,"body":"Well, we, you know,"},{"startTime":2424.48,"endTime":2427.963,"body":"fast-forward 25 years or so,"},{"startTime":2429.01,"endTime":2431.407,"body":"and the sort of, if you like,"},{"startTime":2431.407,"endTime":2436.407,"body":"the sort of reductio ad"},{"startTime":2431.407,"endTime":2436.407,"body":"absurdum of the whole enterprise"},{"startTime":2436.72,"endTime":2438.67,"body":"of the scientific community"},{"startTime":2436.72,"endTime":2438.67,"body":"trying to work out,"},{"startTime":2438.67,"endTime":2442.09,"body":"use climate models to pin"},{"startTime":2438.67,"endTime":2442.09,"body":"down the climate sensitivity"},{"startTime":2442.09,"endTime":2444.04,"body":"was an experiment we led from Oxford"},{"startTime":2444.04,"endTime":2446.8,"body":"back in the mid 2000s called"},{"startTime":2444.04,"endTime":2446.8,"body":"climateprediction.net,"},{"startTime":2446.8,"endTime":2448.54,"body":"and some of you may have"},{"startTime":2446.8,"endTime":2448.54,"body":"actually participated"},{"startTime":2448.54,"endTime":2451.87,"body":"in this experiment, we"},{"startTime":2448.54,"endTime":2451.87,"body":"generated, yeah, thanks,"},{"startTime":2451.87,"endTime":2454.87,"body":"we generated versions of a climate model,"},{"startTime":2454.87,"endTime":2456.94,"body":"distributed them all over the world."},{"startTime":2456.94,"endTime":2459.31,"body":"So people were running these"},{"startTime":2456.94,"endTime":2459.31,"body":"models all over the place."},{"startTime":2459.31,"endTime":2461.38,"body":"There was one even being"},{"startTime":2459.31,"endTime":2461.38,"body":"run at the South Pole,"},{"startTime":2461.38,"endTime":2464.59,"body":"and they all doubled CO2 and"},{"startTime":2461.38,"endTime":2464.59,"body":"sent us their results back"},{"startTime":2464.59,"endTime":2467.11,"body":"to see what warming they got."},{"startTime":2467.11,"endTime":2469.12,"body":"And what was really interesting"},{"startTime":2469.12,"endTime":2471.55,"body":"was that they got this"},{"startTime":2469.12,"endTime":2471.55,"body":"sort of distribution."},{"startTime":2471.55,"endTime":2474.25,"body":"These are the first results"},{"startTime":2471.55,"endTime":2474.25,"body":"we got from the experiment,"},{"startTime":2474.25,"endTime":2476.32,"body":"and they got this distribution"},{"startTime":2476.32,"endTime":2477.76,"body":"of simulated climate sensitivity."},{"startTime":2477.76,"endTime":2482.041,"body":"So remember, this was 1.5 to 4.5 degrees."},{"startTime":2482.041,"endTime":2486.25,"body":"That was Jules Charney's range."},{"startTime":2486.25,"endTime":2487.96,"body":"Arrhenius's estimate was four degrees."},{"startTime":2487.96,"endTime":2491.23,"body":"So lot of support for"},{"startTime":2487.96,"endTime":2491.23,"body":"Jules Charney's range,"},{"startTime":2491.23,"endTime":2496.09,"body":"but this interesting sort"},{"startTime":2491.23,"endTime":2496.09,"body":"of tale of possible warming"},{"startTime":2496.09,"endTime":2498.673,"body":"going out to some"},{"startTime":2496.09,"endTime":2498.673,"body":"ridiculously high numbers,"},{"startTime":2500.35,"endTime":2502.69,"body":"which caused a certain amount"},{"startTime":2500.35,"endTime":2502.69,"body":"of consternation at the time"},{"startTime":2502.69,"endTime":2505.75,"body":"because it showed how"},{"startTime":2502.69,"endTime":2505.75,"body":"difficult it would be"},{"startTime":2505.75,"endTime":2509.86,"body":"to pin down the risk of"},{"startTime":2505.75,"endTime":2509.86,"body":"high climate sensitivity"},{"startTime":2509.86,"endTime":2512.53,"body":"or high level of warming"},{"startTime":2509.86,"endTime":2512.53,"body":"if we were to stabilize"},{"startTime":2512.53,"endTime":2515.98,"body":"greenhouse gas concentrations"},{"startTime":2512.53,"endTime":2515.98,"body":"at any particular level."},{"startTime":2515.98,"endTime":2518.17,"body":"And it's interesting that the"},{"startTime":2515.98,"endTime":2518.17,"body":"latest generation of models"},{"startTime":2518.17,"endTime":2520.78,"body":"over here on the right"},{"startTime":2518.17,"endTime":2520.78,"body":"aren't really helping either."},{"startTime":2520.78,"endTime":2522.76,"body":"I mean, they're not"},{"startTime":2520.78,"endTime":2522.76,"body":"going up to 10 degrees,"},{"startTime":2522.76,"endTime":2525.4,"body":"but they are up at sort"},{"startTime":2522.76,"endTime":2525.4,"body":"of six degrees or so,"},{"startTime":2525.4,"endTime":2528.163,"body":"the highest sensitivities in the models,"},{"startTime":2529.0,"endTime":2530.93,"body":"and you know, well above"},{"startTime":2534.34,"endTime":2535.27,"body":"the upper end of the range"},{"startTime":2535.27,"endTime":2537.943,"body":"that most people think is plausible."},{"startTime":2538.87,"endTime":2543.87,"body":"So this equilibrium climate"},{"startTime":2538.87,"endTime":2543.87,"body":"response is uncertain, okay?"},{"startTime":2544.3,"endTime":2546.013,"body":"But lots of things are uncertain."},{"startTime":2546.94,"endTime":2550.93,"body":"The real problem with the"},{"startTime":2546.94,"endTime":2550.93,"body":"equilibrium climate sensitivity"},{"startTime":2550.93,"endTime":2555.88,"body":"is not that it's uncertain,"},{"startTime":2550.93,"endTime":2555.88,"body":"but that it's contestable,"},{"startTime":2555.88,"endTime":2560.62,"body":"that it's difficult to"},{"startTime":2555.88,"endTime":2560.62,"body":"get everybody to agree"},{"startTime":2560.62,"endTime":2563.8,"body":"on the uncertainty in the"},{"startTime":2560.62,"endTime":2563.8,"body":"equilibrium climate sensitivity."},{"startTime":2563.8,"endTime":2566.26,"body":"And this brings us to a"},{"startTime":2563.8,"endTime":2566.26,"body":"really interesting problem"},{"startTime":2566.26,"endTime":2569.65,"body":"in probability theory, which I'm going to,"},{"startTime":2569.65,"endTime":2571.72,"body":"there's not that many problems in maths"},{"startTime":2571.72,"endTime":2574.19,"body":"that, you know, we can understand"},{"startTime":2575.14,"endTime":2577.42,"body":"unless we're sort of pro mathematicians,"},{"startTime":2577.42,"endTime":2578.65,"body":"but this is one of them."},{"startTime":2578.65,"endTime":2580.21,"body":"And so suppose you're driving a car"},{"startTime":2580.21,"endTime":2583.09,"body":"with a dodgy speedometer, and you know,"},{"startTime":2583.09,"endTime":2585.58,"body":"okay, so distance equals"},{"startTime":2583.09,"endTime":2585.58,"body":"speed times journey-time."},{"startTime":2585.58,"endTime":2586.88,"body":"You're familiar with that."},{"startTime":2589.061,"endTime":2590.89,"body":"So you've got 40 miles to go."},{"startTime":2590.89,"endTime":2593.38,"body":"You know the distance"},{"startTime":2590.89,"endTime":2593.38,"body":"you've got to travel."},{"startTime":2593.38,"endTime":2595.12,"body":"The speedo says your speed's somewhere"},{"startTime":2595.12,"endTime":2597.64,"body":"between 20 and 40 miles per hour."},{"startTime":2597.64,"endTime":2598.473,"body":"I did this last night,"},{"startTime":2598.473,"endTime":2600.55,"body":"so I really hope I haven't"},{"startTime":2598.473,"endTime":2600.55,"body":"made a mistake in the maths."},{"startTime":2600.55,"endTime":2604.0,"body":"Anyway, so the journey will"},{"startTime":2600.55,"endTime":2604.0,"body":"take between one and two hours."},{"startTime":2604.0,"endTime":2605.83,"body":"So far so good."},{"startTime":2605.83,"endTime":2608.29,"body":"You're meant to arrive in 1 1/2 hours."},{"startTime":2608.29,"endTime":2610.64,"body":"What are the chances that"},{"startTime":2608.29,"endTime":2610.64,"body":"you're going to be late?"},{"startTime":2611.5,"endTime":2613.2,"body":"Who'd like to answer the question?"},{"startTime":2615.94,"endTime":2617.083,"body":"Someone be brave."},{"startTime":2618.82,"endTime":2620.416,"body":"By the way, I'm willing to accept"},{"startTime":2620.416,"endTime":2622.977,"body":"either of the obvious answers,"},{"startTime":2622.977,"endTime":2625.0,"body":"and I've got both of them covered up."},{"startTime":2625.0,"endTime":2627.463,"body":"So go for it. You can't go wrong."},{"startTime":2629.957,"endTime":2630.85,"body":"- [Audience Member] 30."},{"startTime":2630.85,"endTime":2632.094,"body":"- 30."},{"startTime":2632.094,"endTime":2633.52,"body":"(audience member speaking faintly)"},{"startTime":2633.52,"endTime":2635.77,"body":"You're meant to, you're going to arrive,"},{"startTime":2635.77,"endTime":2638.29,"body":"the journey will take"},{"startTime":2635.77,"endTime":2638.29,"body":"between one and two hours."},{"startTime":2638.29,"endTime":2641.23,"body":"You're going to be late"},{"startTime":2638.29,"endTime":2641.23,"body":"if you're more than,"},{"startTime":2641.23,"endTime":2642.82,"body":"you're meant to arrive in 1 1/2 hours."},{"startTime":2642.82,"endTime":2645.4,"body":"What are the chances"},{"startTime":2642.82,"endTime":2645.4,"body":"you're going to be late?"},{"startTime":2645.4,"endTime":2646.843,"body":"Somebody said 50%, okay."},{"startTime":2647.8,"endTime":2651.133,"body":"Does anybody want, do I"},{"startTime":2647.8,"endTime":2651.133,"body":"have any other offers?"},{"startTime":2652.623,"endTime":2653.78,"body":"- [Audience Member] 37 1/2%,"},{"startTime":2653.78,"endTime":2657.769,"body":"assuming it's a uniform"},{"startTime":2653.78,"endTime":2657.769,"body":"distribution (speaking faintly)."},{"startTime":2657.769,"endTime":2661.27,"body":"- Okay, so someone's concentrating."},{"startTime":2661.27,"endTime":2664.3,"body":"If you assume all arrival"},{"startTime":2661.27,"endTime":2664.3,"body":"times in the range"},{"startTime":2664.3,"endTime":2667.57,"body":"are equally likely, yes, 50%."},{"startTime":2667.57,"endTime":2670.63,"body":"If you assume all speeds in the range"},{"startTime":2670.63,"endTime":2674.713,"body":"are equally likely,"},{"startTime":2670.63,"endTime":2674.713,"body":"33%, yeah, more or less."},{"startTime":2676.432,"endTime":2678.903,"body":"No, no, no, no, you're good,"},{"startTime":2676.432,"endTime":2678.903,"body":"you're good, you're good."},{"startTime":2680.05,"endTime":2682.84,"body":"So which is correct?"},{"startTime":2682.84,"endTime":2687.22,"body":"All you're told is it's"},{"startTime":2682.84,"endTime":2687.22,"body":"a rubbish speedometer."},{"startTime":2687.22,"endTime":2692.05,"body":"If it says 30, it could be"},{"startTime":2687.22,"endTime":2692.05,"body":"anywhere between 20 and 40."},{"startTime":2692.05,"endTime":2695.653,"body":"If that's all you're told,"},{"startTime":2692.05,"endTime":2695.653,"body":"which of these is correct?"},{"startTime":2698.68,"endTime":2700.54,"body":"And by the way, I'm not"},{"startTime":2698.68,"endTime":2700.54,"body":"going to tell you the answer"},{"startTime":2700.54,"endTime":2704.5,"body":"to that question because I"},{"startTime":2700.54,"endTime":2704.5,"body":"don't know what it is, okay?"},{"startTime":2704.5,"endTime":2706.96,"body":"Well, some people argue"},{"startTime":2704.5,"endTime":2706.96,"body":"that there is an answer."},{"startTime":2706.96,"endTime":2709.66,"body":"Let me just show you, it"},{"startTime":2706.96,"endTime":2709.66,"body":"gets even more interesting"},{"startTime":2709.66,"endTime":2711.58,"body":"if we talk about smaller probabilities."},{"startTime":2711.58,"endTime":2715.33,"body":"So suppose instead of you'll be late,"},{"startTime":2715.33,"endTime":2717.11,"body":"you'll get fired if you arrive"},{"startTime":2718.977,"endTime":2721.81,"body":"in more than 1.9 hours, okay?"},{"startTime":2721.81,"endTime":2723.34,"body":"So what are the odds"},{"startTime":2721.81,"endTime":2723.34,"body":"you're going to get fired?"},{"startTime":2723.34,"endTime":2725.08,"body":"This is a really bad outcome."},{"startTime":2725.08,"endTime":2726.82,"body":"Well, if you assume all arrival times"},{"startTime":2726.82,"endTime":2729.01,"body":"are equally likely, 10%,"},{"startTime":2729.01,"endTime":2730.273,"body":"'cause between one hour and two hours,"},{"startTime":2730.273,"endTime":2735.04,"body":"1.9, 10%, yeah, the margin, okay?"},{"startTime":2735.04,"endTime":2737.95,"body":"If you assume all speeds"},{"startTime":2735.04,"endTime":2737.95,"body":"are equally likely,"},{"startTime":2737.95,"endTime":2739.84,"body":"I won't force you to do this one,"},{"startTime":2739.84,"endTime":2742.69,"body":"but it's about 5%, 5.2%, okay?"},{"startTime":2742.69,"endTime":2745.52,"body":"So factor of two difference in probability"},{"startTime":2746.53,"endTime":2749.08,"body":"just based on what you assume"},{"startTime":2749.08,"endTime":2753.463,"body":"your ignorance means, okay?"},{"startTime":2754.6,"endTime":2756.25,"body":"Now, let's think of another problem"},{"startTime":2756.25,"endTime":2759.01,"body":"which may seem slightly more"},{"startTime":2756.25,"endTime":2759.01,"body":"relevant to this lecture."},{"startTime":2759.01,"endTime":2762.94,"body":"Today's level of energy imbalance"},{"startTime":2759.01,"endTime":2762.94,"body":"due to human activity is,"},{"startTime":2762.94,"endTime":2764.59,"body":"depending on exactly"},{"startTime":2762.94,"endTime":2764.59,"body":"where you measure it from,"},{"startTime":2764.59,"endTime":2767.143,"body":"roughly 2.8 watts per square meter."},{"startTime":2768.49,"endTime":2771.82,"body":"Just rearranging those"},{"startTime":2768.49,"endTime":2771.82,"body":"equations from before,"},{"startTime":2771.82,"endTime":2773.14,"body":"I'll call it Fnow."},{"startTime":2773.14,"endTime":2776.17,"body":"That's the extra energy"},{"startTime":2773.14,"endTime":2776.17,"body":"flowing into the climate system"},{"startTime":2776.17,"endTime":2778.27,"body":"as a result of past increases"},{"startTime":2778.27,"endTime":2779.56,"body":"in greenhouse gas concentrations"},{"startTime":2779.56,"endTime":2782.26,"body":"and other forms of anthropogenic pollution"},{"startTime":2782.26,"endTime":2783.16,"body":"in the atmosphere."},{"startTime":2784.151,"endTime":2788.02,"body":"So if we were to stop"},{"startTime":2784.151,"endTime":2788.02,"body":"the atmosphere changing"},{"startTime":2788.02,"endTime":2792.91,"body":"and hold it at today's"},{"startTime":2788.02,"endTime":2792.91,"body":"concentrations of everything forever,"},{"startTime":2792.91,"endTime":2794.41,"body":"how much warming would we get?"},{"startTime":2795.31,"endTime":2796.93,"body":"Well, that's going to depend"},{"startTime":2796.93,"endTime":2799.99,"body":"on this equilibrium climate sensitivity."},{"startTime":2799.99,"endTime":2802.27,"body":"So suppose the equilibrium"},{"startTime":2799.99,"endTime":2802.27,"body":"climate sensitivity"},{"startTime":2802.27,"endTime":2804.16,"body":"is 1.5 to 4.5 degrees,"},{"startTime":2804.16,"endTime":2807.52,"body":"and suppose the extra energy"},{"startTime":2804.16,"endTime":2807.52,"body":"flow from a doubling of CO2"},{"startTime":2807.52,"endTime":2809.44,"body":"is 3.7 watts per meter squared,"},{"startTime":2809.44,"endTime":2812.29,"body":"what are the odds of"},{"startTime":2809.44,"endTime":2812.29,"body":"this equilibrium warming"},{"startTime":2812.29,"endTime":2814.93,"body":"with today's concentrations"},{"startTime":2812.29,"endTime":2814.93,"body":"of greenhouse gases alone?"},{"startTime":2814.93,"endTime":2818.74,"body":"And by the way, these are"},{"startTime":2814.93,"endTime":2818.74,"body":"sort of illustrative examples."},{"startTime":2818.74,"endTime":2820.06,"body":"So you can do the maths in your head,"},{"startTime":2820.06,"endTime":2822.07,"body":"which I'm sure you're all doing right now,"},{"startTime":2822.07,"endTime":2823.45,"body":"that these are not the actual"},{"startTime":2823.45,"endTime":2827.65,"body":"sort of canonical distributions"},{"startTime":2823.45,"endTime":2827.65,"body":"people accept at the moment."},{"startTime":2827.65,"endTime":2831.73,"body":"So all, if we assume all values of lambda,"},{"startTime":2831.73,"endTime":2834.403,"body":"of the sensitivity"},{"startTime":2831.73,"endTime":2834.403,"body":"parameter equally likely,"},{"startTime":2835.3,"endTime":2839.443,"body":"we get 7% risk of temperatures"},{"startTime":2835.3,"endTime":2839.443,"body":"going above three degrees."},{"startTime":2840.43,"endTime":2845.43,"body":"If we assume all values of"},{"startTime":2840.43,"endTime":2845.43,"body":"the climate sensitivity,"},{"startTime":2845.56,"endTime":2848.593,"body":"the warming due to doubling"},{"startTime":2845.56,"endTime":2848.593,"body":"CO2 are equally likely,"},{"startTime":2849.52,"endTime":2850.78,"body":"you won't have done all"},{"startTime":2849.52,"endTime":2850.78,"body":"the maths in your head,"},{"startTime":2850.78,"endTime":2852.01,"body":"but what are you expecting here?"},{"startTime":2852.01,"endTime":2854.56,"body":"Is that going to be a higher"},{"startTime":2852.01,"endTime":2854.56,"body":"number or a lower number?"},{"startTime":2859.54,"endTime":2860.53,"body":"Did somebody say higher?"},{"startTime":2860.53,"endTime":2862.683,"body":"I'm going to pretend you"},{"startTime":2860.53,"endTime":2862.683,"body":"did, well done, okay?"},{"startTime":2863.92,"endTime":2867.67,"body":"So again, a factor of two difference"},{"startTime":2867.67,"endTime":2871.63,"body":"in the risk just arising"},{"startTime":2867.67,"endTime":2871.63,"body":"from what you assume"},{"startTime":2871.63,"endTime":2873.283,"body":"your ignorance looks like."},{"startTime":2874.45,"endTime":2879.22,"body":"Now, so this is the problem"},{"startTime":2874.45,"endTime":2879.22,"body":"with this equilibrium response."},{"startTime":2879.22,"endTime":2880.75,"body":"It's not just that it's uncertain."},{"startTime":2880.75,"endTime":2881.65,"body":"Lots of things are uncertain."},{"startTime":2881.65,"endTime":2883.06,"body":"We deal with uncertainty all the time."},{"startTime":2883.06,"endTime":2886.21,"body":"It's the uncertainty in"},{"startTime":2883.06,"endTime":2886.21,"body":"climate sensitivity itself"},{"startTime":2886.21,"endTime":2889.21,"body":"is contestable because"},{"startTime":2886.21,"endTime":2889.21,"body":"the answer seems to depend"},{"startTime":2889.21,"endTime":2891.19,"body":"on sort of subjective decisions"},{"startTime":2891.19,"endTime":2893.11,"body":"about how you set the problem up."},{"startTime":2893.11,"endTime":2895.24,"body":"What's even worse is it's even contested"},{"startTime":2895.24,"endTime":2896.74,"body":"whether it's contestable."},{"startTime":2896.74,"endTime":2897.767,"body":"So there are people out there who say,"},{"startTime":2897.767,"endTime":2898.6,"body":"\"No, it's not contestable."},{"startTime":2898.6,"endTime":2900.82,"body":"You have to use this system,\" okay?"},{"startTime":2900.82,"endTime":2903.64,"body":"And for example, a big"},{"startTime":2900.82,"endTime":2903.64,"body":"school of statistics"},{"startTime":2903.64,"endTime":2906.88,"body":"says, \"Yes, this was all solved"},{"startTime":2903.64,"endTime":2906.88,"body":"by Edwin Jaynes in 1970,\""},{"startTime":2906.88,"endTime":2908.71,"body":"except that Jaynes's"},{"startTime":2906.88,"endTime":2908.71,"body":"solution has been contested"},{"startTime":2908.71,"endTime":2911.62,"body":"by a paper published"},{"startTime":2908.71,"endTime":2911.62,"body":"by Alon Drury in 2015."},{"startTime":2911.62,"endTime":2916.18,"body":"Not many bits of maths we can"},{"startTime":2911.62,"endTime":2916.18,"body":"sort of get our minds around"},{"startTime":2916.18,"endTime":2918.46,"body":"more or less are contested by papers"},{"startTime":2918.46,"endTime":2920.68,"body":"published in the past decade."},{"startTime":2920.68,"endTime":2924.79,"body":"This is out there. This is"},{"startTime":2920.68,"endTime":2924.79,"body":"still being argued over."},{"startTime":2924.79,"endTime":2926.41,"body":"So the argument continues."},{"startTime":2926.41,"endTime":2930.1,"body":"Over on the right here,"},{"startTime":2926.41,"endTime":2930.1,"body":"that sort of 2.6 to 4.1,"},{"startTime":2930.1,"endTime":2932.23,"body":"that's the sort of canonical range"},{"startTime":2932.23,"endTime":2934.3,"body":"of climate sensitivity in the most recent"},{"startTime":2934.3,"endTime":2935.95,"body":"Intergovernmental Panel on Climate Change,"},{"startTime":2935.95,"endTime":2937.61,"body":"and it came out of a big study"},{"startTime":2939.79,"endTime":2944.79,"body":"which was initiated in a"},{"startTime":2939.79,"endTime":2944.79,"body":"meeting in a castle in Bavaria."},{"startTime":2945.79,"endTime":2947.71,"body":"They gathered together all the scientists"},{"startTime":2947.71,"endTime":2950.26,"body":"who'd been thinking about"},{"startTime":2947.71,"endTime":2950.26,"body":"climate sensitivity."},{"startTime":2950.26,"endTime":2953.02,"body":"It was the Max Planck Institute gathered,"},{"startTime":2953.02,"endTime":2956.56,"body":"and I was in on the original meeting,"},{"startTime":2956.56,"endTime":2958.3,"body":"and it was a very interesting meeting."},{"startTime":2958.3,"endTime":2960.7,"body":"We all talked about the"},{"startTime":2958.3,"endTime":2960.7,"body":"different lines of evidence,"},{"startTime":2960.7,"endTime":2963.29,"body":"and then a team from the meeting went off"},{"startTime":2964.706,"endTime":2967.24,"body":"to develop this paper, Sherwood, et al.,"},{"startTime":2967.24,"endTime":2968.83,"body":"which was the outcome."},{"startTime":2968.83,"endTime":2969.88,"body":"I wasn't involved in the paper,"},{"startTime":2969.88,"endTime":2971.71,"body":"I guess because the last thing you want"},{"startTime":2971.71,"endTime":2972.82,"body":"on an author team for a paper"},{"startTime":2972.82,"endTime":2973.997,"body":"is somebody who just sits"},{"startTime":2972.82,"endTime":2973.997,"body":"in the corner and says,"},{"startTime":2973.997,"endTime":2976.39,"body":"\"This is all pointless. I don't care.\""},{"startTime":2976.39,"endTime":2978.97,"body":"So, but that is my view on"},{"startTime":2976.39,"endTime":2978.97,"body":"the climate sensitivity."},{"startTime":2978.97,"endTime":2981.82,"body":"I think it's a daft question."},{"startTime":2981.82,"endTime":2984.64,"body":"And of course as recently"},{"startTime":2981.82,"endTime":2984.64,"body":"as a couple of months ago,"},{"startTime":2984.64,"endTime":2988.03,"body":"a new estimate using"},{"startTime":2984.64,"endTime":2988.03,"body":"identical data has emerged,"},{"startTime":2988.03,"endTime":2989.71,"body":"but just different statistical methods"},{"startTime":2989.71,"endTime":2991.18,"body":"and statistical assumptions,"},{"startTime":2991.18,"endTime":2993.82,"body":"which gives us a very different range."},{"startTime":2993.82,"endTime":2997.09,"body":"So it's difficult to estimate"},{"startTime":2997.09,"endTime":3001.95,"body":"this long-term equilibrium"},{"startTime":2997.09,"endTime":3001.95,"body":"warming of the climate system,"},{"startTime":3001.95,"endTime":3004.35,"body":"even when we take into"},{"startTime":3001.95,"endTime":3004.35,"body":"account additional information"},{"startTime":3004.35,"endTime":3007.86,"body":"from that which is just given"},{"startTime":3004.35,"endTime":3007.86,"body":"us by our climate models."},{"startTime":3007.86,"endTime":3009.96,"body":"Why does this matter?"},{"startTime":3009.96,"endTime":3013.8,"body":"Well, back in 1992, not long after,"},{"startTime":3013.8,"endTime":3017.52,"body":"well, a decade, 13 years"},{"startTime":3013.8,"endTime":3017.52,"body":"after the Charney report,"},{"startTime":3017.52,"endTime":3020.7,"body":"but at a time when the only"},{"startTime":3017.52,"endTime":3020.7,"body":"experiments we could do"},{"startTime":3020.7,"endTime":3022.297,"body":"with climate models was double CO2"},{"startTime":3022.297,"endTime":3024.36,"body":"and see how much they warmed up,"},{"startTime":3024.36,"endTime":3026.82,"body":"the Rio Convention was written,"},{"startTime":3026.82,"endTime":3029.88,"body":"and that contained this crucial line"},{"startTime":3029.88,"endTime":3032.49,"body":"that the parties were"},{"startTime":3029.88,"endTime":3032.49,"body":"aiming for stabilization"},{"startTime":3032.49,"endTime":3034.44,"body":"of greenhouse gas"},{"startTime":3032.49,"endTime":3034.44,"body":"concentrations in the atmosphere"},{"startTime":3034.44,"endTime":3037.53,"body":"at a level that would prevent dangerous"},{"startTime":3037.53,"endTime":3040.62,"body":"anthropogenic interference"},{"startTime":3037.53,"endTime":3040.62,"body":"in the climate system."},{"startTime":3040.62,"endTime":3043.237,"body":"And so immediately the"},{"startTime":3040.62,"endTime":3043.237,"body":"scientific community thought,"},{"startTime":3043.237,"endTime":3046.47,"body":"\"Well, we've clearly got to"},{"startTime":3043.237,"endTime":3046.47,"body":"work out what that level is,\""},{"startTime":3046.47,"endTime":3049.22,"body":"which meant we had to work"},{"startTime":3046.47,"endTime":3049.22,"body":"out the climate sensitivity."},{"startTime":3051.21,"endTime":3054.15,"body":"Fortunately, it turns out we don't,"},{"startTime":3054.15,"endTime":3056.16,"body":"and this is the change of the subject"},{"startTime":3056.16,"endTime":3057.51,"body":"that we will be going through"},{"startTime":3057.51,"endTime":3060.96,"body":"in the next two Gresham lectures."},{"startTime":3060.96,"endTime":3064.32,"body":"But unfortunately, like"},{"startTime":3060.96,"endTime":3064.32,"body":"the thing from the crypt,"},{"startTime":3064.32,"endTime":3066.99,"body":"it's coming back to haunt us even today."},{"startTime":3066.99,"endTime":3069.15,"body":"So the equilibrium climate sensitivity,"},{"startTime":3069.15,"endTime":3071.28,"body":"this very-long-term equilibrium response,"},{"startTime":3071.28,"endTime":3074.07,"body":"only matters if we actually stabilize"},{"startTime":3074.07,"endTime":3076.56,"body":"atmospheric concentrations"},{"startTime":3074.07,"endTime":3076.56,"body":"of greenhouse gases"},{"startTime":3076.56,"endTime":3078.24,"body":"and allow the climate to re-equilibrate,"},{"startTime":3078.24,"endTime":3080.52,"body":"which takes many, many centuries."},{"startTime":3080.52,"endTime":3082.14,"body":"The breakthrough in the late 2000s,"},{"startTime":3082.14,"endTime":3085.26,"body":"which led us to net"},{"startTime":3082.14,"endTime":3085.26,"body":"zero, was the realization"},{"startTime":3085.26,"endTime":3086.91,"body":"that we can actually stop the warming"},{"startTime":3086.91,"endTime":3089.94,"body":"well before restoring climate equilibrium"},{"startTime":3089.94,"endTime":3093.213,"body":"if we reduce anthropogenic"},{"startTime":3089.94,"endTime":3093.213,"body":"emissions to net zero."},{"startTime":3094.8,"endTime":3098.94,"body":"Unfortunately, there's a catch."},{"startTime":3098.94,"endTime":3100.95,"body":"That assumption was we were talking"},{"startTime":3100.95,"endTime":3102.72,"body":"about anthropogenic emissions,"},{"startTime":3102.72,"endTime":3107.72,"body":"assuming that carbon dioxide"},{"startTime":3102.72,"endTime":3107.72,"body":"that was taken up by plants"},{"startTime":3107.82,"endTime":3111.15,"body":"or oceans would just"},{"startTime":3107.82,"endTime":3111.15,"body":"count as natural uptake,"},{"startTime":3111.15,"endTime":3115.05,"body":"even if it was being taken up"},{"startTime":3111.15,"endTime":3115.05,"body":"faster as a result of the fact"},{"startTime":3115.05,"endTime":3118.2,"body":"there was more carbon"},{"startTime":3115.05,"endTime":3118.2,"body":"dioxide in the atmosphere."},{"startTime":3118.2,"endTime":3121.2,"body":"We'll come back to this in"},{"startTime":3118.2,"endTime":3121.2,"body":"the carbon cycle lecture,"},{"startTime":3121.2,"endTime":3124.35,"body":"but a worrying development is that people,"},{"startTime":3124.35,"endTime":3127.29,"body":"I guess rather naively, when"},{"startTime":3124.35,"endTime":3127.29,"body":"we published those papers,"},{"startTime":3127.29,"endTime":3129.81,"body":"we thought people would"},{"startTime":3127.29,"endTime":3129.81,"body":"be grateful to nature"},{"startTime":3129.81,"endTime":3132.81,"body":"for carbon that was being taken"},{"startTime":3129.81,"endTime":3132.81,"body":"up by trees growing faster"},{"startTime":3132.81,"endTime":3135.72,"body":"and just regard it as something"},{"startTime":3132.81,"endTime":3135.72,"body":"natural that was happening."},{"startTime":3135.72,"endTime":3138.39,"body":"But of course those"},{"startTime":3135.72,"endTime":3138.39,"body":"trees belong to somebody"},{"startTime":3138.39,"endTime":3140.04,"body":"or they belong to a country,"},{"startTime":3140.04,"endTime":3142.41,"body":"and now those countries"},{"startTime":3140.04,"endTime":3142.41,"body":"want to take credit"},{"startTime":3142.41,"endTime":3144.06,"body":"for that carbon uptake."},{"startTime":3144.06,"endTime":3148.53,"body":"And suddenly everybody wants"},{"startTime":3144.06,"endTime":3148.53,"body":"to say that any carbon taken up"},{"startTime":3148.53,"endTime":3151.17,"body":"by anything anywhere"},{"startTime":3148.53,"endTime":3151.17,"body":"is a negative emission"},{"startTime":3151.17,"endTime":3152.913,"body":"and sell it on the offset markets."},{"startTime":3154.08,"endTime":3156.78,"body":"And if we carry on burning fossil fuels"},{"startTime":3156.78,"endTime":3160.5,"body":"and just buying offsets with"},{"startTime":3156.78,"endTime":3160.5,"body":"these natural absorptions"},{"startTime":3160.5,"endTime":3162.75,"body":"being counted as a negative emission,"},{"startTime":3162.75,"endTime":3164.46,"body":"we're right back to where we started,"},{"startTime":3164.46,"endTime":3167.43,"body":"because then net zero only"},{"startTime":3164.46,"endTime":3167.43,"body":"means stabilizing concentrations"},{"startTime":3167.43,"endTime":3169.44,"body":"in the atmosphere, and"},{"startTime":3167.43,"endTime":3169.44,"body":"it's very hard to predict"},{"startTime":3169.44,"endTime":3172.38,"body":"when temperatures would stop"},{"startTime":3169.44,"endTime":3172.38,"body":"rising if we were to do that."},{"startTime":3172.38,"endTime":3174.24,"body":"So I just mention this at the end"},{"startTime":3174.24,"endTime":3178.62,"body":"because it's not often"},{"startTime":3174.24,"endTime":3178.62,"body":"that a basic problem"},{"startTime":3178.62,"endTime":3180.84,"body":"of probability theory, by the way,"},{"startTime":3180.84,"endTime":3182.46,"body":"it's called Bertrand's paradox"},{"startTime":3182.46,"endTime":3184.16,"body":"that I've been talking about here,"},{"startTime":3185.04,"endTime":3189.51,"body":"actually has an impact"},{"startTime":3185.04,"endTime":3189.51,"body":"on global climate policy."},{"startTime":3189.51,"endTime":3192.0,"body":"And it even has an impact when you decide"},{"startTime":3192.0,"endTime":3193.17,"body":"whether or not to check that box"},{"startTime":3193.17,"endTime":3194.64,"body":"next time you take an air flight."},{"startTime":3194.64,"endTime":3196.44,"body":"It's a good idea, why not do it,"},{"startTime":3196.44,"endTime":3198.75,"body":"but just remember it's"},{"startTime":3196.44,"endTime":3198.75,"body":"not really compensating"},{"startTime":3198.75,"endTime":3200.28,"body":"for your emissions."},{"startTime":3200.28,"endTime":3202.26,"body":"So that's what we've tried"},{"startTime":3200.28,"endTime":3202.26,"body":"to cover in this lecture,"},{"startTime":3202.26,"endTime":3203.85,"body":"how rising carbon dioxide concentrations"},{"startTime":3203.85,"endTime":3204.93,"body":"cause global warming,"},{"startTime":3204.93,"endTime":3206.28,"body":"how they actually cause global warming"},{"startTime":3206.28,"endTime":3208.32,"body":"as opposed to the schoolbook picture,"},{"startTime":3208.32,"endTime":3210.66,"body":"why the equilibrium climate sensitivity"},{"startTime":3210.66,"endTime":3212.43,"body":"is so hotly contested."},{"startTime":3212.43,"endTime":3214.74,"body":"And that was the sort of paradigmatic view"},{"startTime":3214.74,"endTime":3216.93,"body":"of climate science and"},{"startTime":3214.74,"endTime":3216.93,"body":"what we were trying to do"},{"startTime":3216.93,"endTime":3218.34,"body":"before net zero."},{"startTime":3218.34,"endTime":3221.997,"body":"So this was the problem"},{"startTime":3218.34,"endTime":3221.997,"body":"we faced in the 2000s"},{"startTime":3221.997,"endTime":3225.99,"body":"and why we moved, changed"},{"startTime":3221.997,"endTime":3225.99,"body":"the subject to net zero."},{"startTime":3225.99,"endTime":3228.84,"body":"And then finally this point"},{"startTime":3225.99,"endTime":3228.84,"body":"about how even, you know,"},{"startTime":3228.84,"endTime":3231.99,"body":"quite fundamental thorny"},{"startTime":3228.84,"endTime":3231.99,"body":"issues in probability theory"},{"startTime":3231.99,"endTime":3236.343,"body":"can actually have big global"},{"startTime":3231.99,"endTime":3236.343,"body":"implications, thank you."},{"startTime":3236.343,"endTime":3239.646,"body":"(audience applauding)"},{"startTime":3239.646,"endTime":3240.81,"body":"- Thanks so much, Professor Allen,"},{"startTime":3240.81,"endTime":3242.07,"body":"for such a fascinating lecture."},{"startTime":3242.07,"endTime":3243.9,"body":"I've got a couple of questions from online"},{"startTime":3243.9,"endTime":3245.91,"body":"before we're going to go to the room."},{"startTime":3245.91,"endTime":3247.567,"body":"So the first question is,"},{"startTime":3247.567,"endTime":3249.93,"body":"\"Do you think the climate"},{"startTime":3247.567,"endTime":3249.93,"body":"sensitivity problem"},{"startTime":3249.93,"endTime":3251.607,"body":"held up climate policy?\""},{"startTime":3253.14,"endTime":3257.1,"body":"- I think it fed into the"},{"startTime":3253.14,"endTime":3257.1,"body":"way the Rio Convention,"},{"startTime":3257.1,"endTime":3258.21,"body":"it's an interesting feedback."},{"startTime":3258.21,"endTime":3260.52,"body":"It fed into the way the"},{"startTime":3258.21,"endTime":3260.52,"body":"Rio Convention was framed,"},{"startTime":3260.52,"endTime":3264.84,"body":"which fed into this A-level, and you know,"},{"startTime":3264.84,"endTime":3266.46,"body":"if that's in the convention,"},{"startTime":3266.46,"endTime":3268.41,"body":"this is an important"},{"startTime":3266.46,"endTime":3268.41,"body":"international document,"},{"startTime":3268.41,"endTime":3271.83,"body":"so of course we all ran"},{"startTime":3268.41,"endTime":3271.83,"body":"around trying to solve it."},{"startTime":3271.83,"endTime":3275.28,"body":"And yes, so I think it,"},{"startTime":3271.83,"endTime":3275.28,"body":"yeah, I think it did,"},{"startTime":3275.28,"endTime":3276.423,"body":"it did hold things up."},{"startTime":3277.886,"endTime":3280.71,"body":"It certainly in my view wasted"},{"startTime":3277.886,"endTime":3280.71,"body":"a lot of scientists' time."},{"startTime":3280.71,"endTime":3282.69,"body":"I should say I have"},{"startTime":3280.71,"endTime":3282.69,"body":"colleagues who get very angry"},{"startTime":3282.69,"endTime":3285.24,"body":"when I say that trying to pin"},{"startTime":3282.69,"endTime":3285.24,"body":"down the climate sensitivity"},{"startTime":3285.24,"endTime":3286.233,"body":"was a waste of time."},{"startTime":3286.233,"endTime":3287.85,"body":"I mean, 'cause they're, \"No,"},{"startTime":3286.233,"endTime":3287.85,"body":"no, we're going to keep trying.\""},{"startTime":3287.85,"endTime":3289.62,"body":"I said, \"Well, yeah, you can"},{"startTime":3287.85,"endTime":3289.62,"body":"search for the holy grail"},{"startTime":3289.62,"endTime":3291.785,"body":"if you want to, but hmm, you know,"},{"startTime":3291.785,"endTime":3293.527,"body":"it may not be that useful"},{"startTime":3291.785,"endTime":3293.527,"body":"when you find it,\" anyway."},{"startTime":3293.527,"endTime":3295.92,"body":"- \"Here in 2021, the world's largest"},{"startTime":3295.92,"endTime":3299.79,"body":"direct air carbon removal"},{"startTime":3295.92,"endTime":3299.79,"body":"plant opened in Iceland."},{"startTime":3299.79,"endTime":3301.08,"body":"According to some calculations,"},{"startTime":3301.08,"endTime":3302.88,"body":"it will capture about three seconds worth"},{"startTime":3302.88,"endTime":3305.94,"body":"of each year's global CO2 emissions."},{"startTime":3305.94,"endTime":3309.72,"body":"Is carbon capture going"},{"startTime":3305.94,"endTime":3309.72,"body":"to get us to net zero?\""},{"startTime":3309.72,"endTime":3312.23,"body":"- It'll have to, but that's the topic"},{"startTime":3312.23,"endTime":3314.43,"body":"of the last Gresham lecture of this year."},{"startTime":3314.43,"endTime":3319.38,"body":"So please come to the final"},{"startTime":3314.43,"endTime":3319.38,"body":"Gresham lecture of this cycle"},{"startTime":3319.38,"endTime":3322.59,"body":"where we talk about how we"},{"startTime":3319.38,"endTime":3322.59,"body":"actually achieve net zero."},{"startTime":3322.59,"endTime":3324.6,"body":"Apologies to that questioner."},{"startTime":3324.6,"endTime":3325.86,"body":"- [Audience Member] How did Arrhenius"},{"startTime":3325.86,"endTime":3329.07,"body":"come up with this number?"},{"startTime":3329.07,"endTime":3332.28,"body":"Did he know, was it a guess, or did he-"},{"startTime":3332.28,"endTime":3334.233,"body":"- I think it was, he was quite lucky."},{"startTime":3335.22,"endTime":3337.8,"body":"Yeah, a number of things"},{"startTime":3335.22,"endTime":3337.8,"body":"in his calculation."},{"startTime":3337.8,"endTime":3340.56,"body":"So he didn't do it using"},{"startTime":3337.8,"endTime":3340.56,"body":"this sort of colored balls"},{"startTime":3340.56,"endTime":3345.56,"body":"in the atmosphere argument,"},{"startTime":3340.56,"endTime":3345.56,"body":"but he did know that,"},{"startTime":3345.6,"endTime":3347.85,"body":"he did take into account"},{"startTime":3345.6,"endTime":3347.85,"body":"changing temperature"},{"startTime":3347.85,"endTime":3349.411,"body":"in the atmosphere."},{"startTime":3349.411,"endTime":3350.73,"body":"And by the way, I should've said,"},{"startTime":3350.73,"endTime":3352.2,"body":"does anybody want to answer the question"},{"startTime":3352.2,"endTime":3355.38,"body":"about Angstrom before we go any further?"},{"startTime":3355.38,"endTime":3357.993,"body":"What was wrong with Angstrom's experiment?"},{"startTime":3359.28,"endTime":3360.15,"body":"- There's someone-"},{"startTime":3359.28,"endTime":3360.15,"body":"- Far away,"},{"startTime":3360.15,"endTime":3360.983,"body":"there's somebody at the back."},{"startTime":3360.983,"endTime":3363.946,"body":"Did you want to answer Angstrom's"},{"startTime":3360.983,"endTime":3363.946,"body":"experiment? Is that okay?"},{"startTime":3363.946,"endTime":3365.706,"body":"- [Audience Member] Is it to do with speed"},{"startTime":3365.706,"endTime":3368.821,"body":"of the molecules as the"},{"startTime":3365.706,"endTime":3368.821,"body":"temperature increases?"},{"startTime":3368.821,"endTime":3373.294,"body":"So the CO2 molecules are moving"},{"startTime":3368.821,"endTime":3373.294,"body":"less distance (indistinct)?"},{"startTime":3373.294,"endTime":3374.713,"body":"- [Moderator] Could you repeat, please?"},{"startTime":3374.713,"endTime":3377.046,"body":"- Is the, yes, so the suggestion was"},{"startTime":3377.046,"endTime":3378.99,"body":"that it was to do with"},{"startTime":3377.046,"endTime":3378.99,"body":"the speed of the molecules"},{"startTime":3378.99,"endTime":3380.7,"body":"and effectively the sort of path length"},{"startTime":3380.7,"endTime":3382.92,"body":"between collisions of molecules."},{"startTime":3382.92,"endTime":3385.38,"body":"That actually does affect the speed"},{"startTime":3385.38,"endTime":3389.25,"body":"with which the absorption density"},{"startTime":3385.38,"endTime":3389.25,"body":"of CO2 varies with height,"},{"startTime":3389.25,"endTime":3391.14,"body":"but it's kind of a more subtle effect."},{"startTime":3391.14,"endTime":3393.6,"body":"No, the big thing that Angstrom got wrong"},{"startTime":3393.6,"endTime":3396.993,"body":"was the temperature of the"},{"startTime":3393.6,"endTime":3396.993,"body":"gas in the pipe was the same,"},{"startTime":3398.37,"endTime":3402.81,"body":"whereas in the atmosphere"},{"startTime":3398.37,"endTime":3402.81,"body":"it cools off by, you know,"},{"startTime":3402.81,"endTime":3406.02,"body":"between the surface, 300,"},{"startTime":3402.81,"endTime":3406.02,"body":"you know, 300 Kelvin,"},{"startTime":3406.02,"endTime":3411.02,"body":"sorry, in familiar units, 15"},{"startTime":3406.02,"endTime":3411.02,"body":"or so degrees at the surface"},{"startTime":3411.48,"endTime":3416.48,"body":"down to minus 70 or so"},{"startTime":3411.48,"endTime":3416.48,"body":"up at the tropopause."},{"startTime":3416.55,"endTime":3418.86,"body":"So we have this huge"},{"startTime":3416.55,"endTime":3418.86,"body":"gradient of temperature"},{"startTime":3418.86,"endTime":3420.226,"body":"in the atmosphere,"},{"startTime":3420.226,"endTime":3422.4,"body":"which of course Angstrom"},{"startTime":3420.226,"endTime":3422.4,"body":"didn't have in his pipe."},{"startTime":3422.4,"endTime":3424.53,"body":"If the atmosphere was"},{"startTime":3422.4,"endTime":3424.53,"body":"all the same temperature,"},{"startTime":3424.53,"endTime":3425.79,"body":"it's true, Angstrom would be right."},{"startTime":3425.79,"endTime":3428.67,"body":"It wouldn't make any difference"},{"startTime":3425.79,"endTime":3428.67,"body":"to add more CO2 to it,"},{"startTime":3428.67,"endTime":3430.41,"body":"because if you think"},{"startTime":3428.67,"endTime":3430.41,"body":"about those colored balls,"},{"startTime":3430.41,"endTime":3431.97,"body":"if they were all the same temperature,"},{"startTime":3431.97,"endTime":3433.89,"body":"if they were all the same color,"},{"startTime":3433.89,"endTime":3436.17,"body":"doubling the concentration"},{"startTime":3433.89,"endTime":3436.17,"body":"wouldn't change the color"},{"startTime":3436.17,"endTime":3437.67,"body":"as you perceive it from the top."},{"startTime":3437.67,"endTime":3439.56,"body":"It'd be just the same color"},{"startTime":3439.56,"endTime":3442.35,"body":"because they were all the"},{"startTime":3439.56,"endTime":3442.35,"body":"same colors to start with."},{"startTime":3442.35,"endTime":3443.64,"body":"So that's what, that's the crucial thing"},{"startTime":3443.64,"endTime":3447.24,"body":"Angstrom got wrong was that he"},{"startTime":3443.64,"endTime":3447.24,"body":"did this elegant experiment,"},{"startTime":3447.24,"endTime":3448.92,"body":"but he left out a crucial ingredient"},{"startTime":3448.92,"endTime":3450.47,"body":"which worked in the real world."},{"startTime":3451.68,"endTime":3453.153,"body":"- [Audience Member] And"},{"startTime":3451.68,"endTime":3453.153,"body":"sorry, yeah, is it true to say"},{"startTime":3453.153,"endTime":3456.627,"body":"that the relationship"},{"startTime":3453.153,"endTime":3456.627,"body":"between the extra CO2 amount"},{"startTime":3456.627,"endTime":3459.57,"body":"and the rising temperature"},{"startTime":3456.627,"endTime":3459.57,"body":"is far from smooth"},{"startTime":3459.57,"endTime":3461.91,"body":"because of tipping points"},{"startTime":3459.57,"endTime":3461.91,"body":"like methane released"},{"startTime":3461.91,"endTime":3465.988,"body":"from melting permafrost or"},{"startTime":3461.91,"endTime":3465.988,"body":"melting ice and things like that?"},{"startTime":3465.988,"endTime":3469.672,"body":"Or are they relatively small"},{"startTime":3465.988,"endTime":3469.672,"body":"effects in the grand scheme?"},{"startTime":3469.672,"endTime":3473.583,"body":"- I mean, if I just, so far,"},{"startTime":3475.65,"endTime":3479.613,"body":"it's been sort of depressingly"},{"startTime":3475.65,"endTime":3479.613,"body":"predictable, if you like."},{"startTime":3480.72,"endTime":3483.39,"body":"And this is of course one of the concerns"},{"startTime":3483.39,"endTime":3485.55,"body":"is that will the climate sort of operate"},{"startTime":3485.55,"endTime":3487.683,"body":"in a sort of a jump thing,"},{"startTime":3489.398,"endTime":3494.398,"body":"like a bad vehicle sort of"},{"startTime":3489.398,"endTime":3494.398,"body":"lurching forwards and so on?"},{"startTime":3496.38,"endTime":3500.79,"body":"But most of the models we have,"},{"startTime":3500.79,"endTime":3503.67,"body":"at least for sort of"},{"startTime":3500.79,"endTime":3503.67,"body":"low levels of warming,"},{"startTime":3503.67,"endTime":3505.84,"body":"warm up fairly predictably"},{"startTime":3506.73,"endTime":3508.98,"body":"up to sort of two or three degrees."},{"startTime":3508.98,"endTime":3511.173,"body":"Beyond that, I think it's kind of,"},{"startTime":3512.46,"endTime":3514.605,"body":"beyond that, there'd be dragons, yeah?"},{"startTime":3514.605,"endTime":3518.67,"body":"I mean, I wouldn't want to"},{"startTime":3514.605,"endTime":3518.67,"body":"give too many assurances."},{"startTime":3518.67,"endTime":3520.62,"body":"But that's what the model,"},{"startTime":3518.67,"endTime":3520.62,"body":"we've not been there."},{"startTime":3520.62,"endTime":3523.44,"body":"We've not tried this experiment"},{"startTime":3520.62,"endTime":3523.44,"body":"on the real world before."},{"startTime":3523.44,"endTime":3524.523,"body":"So we don't know."},{"startTime":3525.75,"endTime":3527.88,"body":"- Professor Allen, we"},{"startTime":3525.75,"endTime":3527.88,"body":"have one more from online,"},{"startTime":3527.88,"endTime":3530.347,"body":"which I'm going to ask you now."},{"startTime":3530.347,"endTime":3533.52,"body":"\"Why does carbon dioxide not act equally"},{"startTime":3533.52,"endTime":3535.467,"body":"as two-way insulation?\""},{"startTime":3537.84,"endTime":3541.773,"body":"- Well, it does in the sense"},{"startTime":3537.84,"endTime":3541.773,"body":"that it absorbs energy,"},{"startTime":3543.36,"endTime":3545.52,"body":"depending on, I'm not quite"},{"startTime":3543.36,"endTime":3545.52,"body":"sure what you mean by two-way,"},{"startTime":3545.52,"endTime":3547.62,"body":"but it does absorb energy going up"},{"startTime":3547.62,"endTime":3549.57,"body":"in the same way it"},{"startTime":3547.62,"endTime":3549.57,"body":"absorbs energy going down,"},{"startTime":3549.57,"endTime":3552.78,"body":"but crucially, there's"},{"startTime":3549.57,"endTime":3552.78,"body":"much more energy going up"},{"startTime":3552.78,"endTime":3555.18,"body":"because the surface is"},{"startTime":3552.78,"endTime":3555.18,"body":"much warmer than space."},{"startTime":3555.18,"endTime":3559.32,"body":"Space is really cold, four degrees Kelvin,"},{"startTime":3559.32,"endTime":3563.133,"body":"so minus 269 Centigrade."},{"startTime":3564.51,"endTime":3567.63,"body":"So, you know, that's"},{"startTime":3564.51,"endTime":3567.63,"body":"why most of the energy"},{"startTime":3567.63,"endTime":3569.7,"body":"that a carbon dioxide molecule encounters"},{"startTime":3569.7,"endTime":3571.68,"body":"as it sort of wanders around"},{"startTime":3569.7,"endTime":3571.68,"body":"through the atmosphere"},{"startTime":3571.68,"endTime":3573.84,"body":"is coming up from below."},{"startTime":3573.84,"endTime":3577.98,"body":"If you're meaning that the,"},{"startTime":3573.84,"endTime":3577.98,"body":"why doesn't carbon dioxide"},{"startTime":3577.98,"endTime":3580.11,"body":"not interact with visible light,"},{"startTime":3580.11,"endTime":3582.57,"body":"that's actually, why does"},{"startTime":3580.11,"endTime":3582.57,"body":"it prefer to interact"},{"startTime":3582.57,"endTime":3584.97,"body":"with infrared light, not visible light?"},{"startTime":3584.97,"endTime":3587.27,"body":"That's actually a really"},{"startTime":3584.97,"endTime":3587.27,"body":"interesting question."},{"startTime":3588.15,"endTime":3591.24,"body":"I mean, hmm, and really to answer that,"},{"startTime":3591.24,"endTime":3593.76,"body":"you sort of get to the"},{"startTime":3591.24,"endTime":3593.76,"body":"point in the road where you,"},{"startTime":3593.76,"endTime":3595.89,"body":"the sort of signs say you"},{"startTime":3593.76,"endTime":3595.89,"body":"can't really go further"},{"startTime":3595.89,"endTime":3596.94,"body":"without quantum mechanics."},{"startTime":3596.94,"endTime":3599.523,"body":"But I mean, just to give you an idea,"},{"startTime":3601.138,"endTime":3602.19,"body":"the carbon dioxide molecules,"},{"startTime":3602.19,"endTime":3606.24,"body":"because it's a three molecule,"},{"startTime":3602.19,"endTime":3606.24,"body":"it's a three-atom molecule,"},{"startTime":3606.24,"endTime":3609.123,"body":"so it can bend in all kinds of ways,"},{"startTime":3610.925,"endTime":3613.23,"body":"and it's sort of relatively floppy"},{"startTime":3613.23,"endTime":3616.14,"body":"compared to, say, an oxygen"},{"startTime":3613.23,"endTime":3616.14,"body":"or nitrogen molecule,"},{"startTime":3616.14,"endTime":3619.35,"body":"which can only really"},{"startTime":3616.14,"endTime":3619.35,"body":"do sort of one thing."},{"startTime":3619.35,"endTime":3623.49,"body":"So that's why carbon"},{"startTime":3619.35,"endTime":3623.49,"body":"dioxide can, if you like,"},{"startTime":3623.49,"endTime":3628.49,"body":"resonate to lower frequency,"},{"startTime":3623.49,"endTime":3628.49,"body":"at lower frequencies"},{"startTime":3628.77,"endTime":3632.07,"body":"than an oxygen or nitrogen molecule can,"},{"startTime":3632.07,"endTime":3636.33,"body":"which is why, if you imagine"},{"startTime":3632.07,"endTime":3636.33,"body":"a floppy guitar string,"},{"startTime":3636.33,"endTime":3640.47,"body":"a loose guitar string"},{"startTime":3636.33,"endTime":3640.47,"body":"gives a deeper, longer,"},{"startTime":3640.47,"endTime":3642.69,"body":"a deeper and lower frequency note"},{"startTime":3642.69,"endTime":3644.4,"body":"than a tight guitar string, yeah?"},{"startTime":3644.4,"endTime":3646.76,"body":"So an oxygen or nitrogen molecule"},{"startTime":3646.76,"endTime":3648.3,"body":"is like a tight guitar string."},{"startTime":3648.3,"endTime":3651.349,"body":"It can only do really high"},{"startTime":3648.3,"endTime":3651.349,"body":"frequencies, visible light."},{"startTime":3651.349,"endTime":3652.68,"body":"It can only, well, it"},{"startTime":3651.349,"endTime":3652.68,"body":"doesn't even interact"},{"startTime":3652.68,"endTime":3653.513,"body":"with visible light."},{"startTime":3653.513,"endTime":3655.29,"body":"It interacts with"},{"startTime":3653.513,"endTime":3655.29,"body":"ultraviolet, that's about it."},{"startTime":3655.29,"endTime":3658.74,"body":"It doesn't really interact"},{"startTime":3655.29,"endTime":3658.74,"body":"with very much at all."},{"startTime":3658.74,"endTime":3662.03,"body":"Whereas the carbon dioxide"},{"startTime":3658.74,"endTime":3662.03,"body":"molecule, it's floppier,"},{"startTime":3662.03,"endTime":3665.43,"body":"so it can resonate at"},{"startTime":3662.03,"endTime":3665.43,"body":"these lower frequencies"},{"startTime":3665.43,"endTime":3667.02,"body":"that are associated with infrared light."},{"startTime":3667.02,"endTime":3669.42,"body":"So that's the big"},{"startTime":3667.02,"endTime":3669.42,"body":"difference between carbon,"},{"startTime":3669.42,"endTime":3672.84,"body":"but interestingly, if"},{"startTime":3669.42,"endTime":3672.84,"body":"you shine visible light"},{"startTime":3672.84,"endTime":3673.8,"body":"at a carbon dioxide molecule,"},{"startTime":3673.8,"endTime":3677.067,"body":"that barely notices"},{"startTime":3673.8,"endTime":3677.067,"body":"because the light is too,"},{"startTime":3677.067,"endTime":3678.933,"body":"the frequency is too high."},{"startTime":3679.92,"endTime":3681.57,"body":"- Professor Allen, thank you so much."},{"startTime":3681.57,"endTime":3683.97,"body":"I'm afraid that's all the time"},{"startTime":3681.57,"endTime":3683.97,"body":"we have for questions now,"},{"startTime":3683.97,"endTime":3686.46,"body":"but please do come and"},{"startTime":3683.97,"endTime":3686.46,"body":"ask any further questions"},{"startTime":3686.46,"endTime":3688.92,"body":"to Professor Allen in person."},{"startTime":3688.92,"endTime":3691.47,"body":"I'm going to remind you about"},{"startTime":3688.92,"endTime":3691.47,"body":"the date of his next lecture,"},{"startTime":3691.47,"endTime":3694.2,"body":"which is, it's the Ocean"},{"startTime":3691.47,"endTime":3694.2,"body":"Physics Behind Net Zero"},{"startTime":3694.2,"endTime":3696.24,"body":"on the 31st of January."},{"startTime":3696.24,"endTime":3698.49,"body":"And I believe that's going to be here,"},{"startTime":3698.49,"endTime":3701.07,"body":"but do check our website."},{"startTime":3701.07,"endTime":3703.782,"body":"- And that is when we uncork the ocean."},{"startTime":3703.782,"endTime":3705.895,"body":"(audience laughs)"},{"startTime":3705.895,"endTime":3710.895,"body":"- Thank you very much."},{"startTime":3705.895,"endTime":3710.895,"body":"(audience applauding)"}]}