{"version":"1.0.0","segments":[{"startTime":0.502,"endTime":3.169,"body":"(intense music)"},{"startTime":5.73,"endTime":6.907,"body":"- In this lecture, we're talking about,"},{"startTime":6.907,"endTime":10.2,"body":"\"The Ocean Physics behind Net Zero.\""},{"startTime":10.2,"endTime":12.663,"body":"And I'd like to start off with a question."},{"startTime":13.77,"endTime":16.2,"body":"Which probably not something"},{"startTime":13.77,"endTime":16.2,"body":"you've thought about very much,"},{"startTime":16.2,"endTime":18.813,"body":"but why is the deep ocean cold?"},{"startTime":20.52,"endTime":22.41,"body":"You probably think you know"},{"startTime":20.52,"endTime":22.41,"body":"the answer to this question."},{"startTime":22.41,"endTime":26.8,"body":"Well, it must be cold because"},{"startTime":22.41,"endTime":26.8,"body":"the sun can't get down there."},{"startTime":26.8,"endTime":28.26,"body":"All the heat from the sun,"},{"startTime":28.26,"endTime":31.14,"body":"is absorbed in the top few millimeters,"},{"startTime":31.14,"endTime":32.37,"body":"in fact of the ocean,"},{"startTime":32.37,"endTime":35.97,"body":"and the mixing by the"},{"startTime":32.37,"endTime":35.97,"body":"wind only takes it down,"},{"startTime":35.97,"endTime":39.3,"body":"top few tens of meters."},{"startTime":39.3,"endTime":41.01,"body":"But if you think about it,"},{"startTime":41.01,"endTime":45.783,"body":"that only explains why the"},{"startTime":41.01,"endTime":45.783,"body":"deep ocean isn't warming up."},{"startTime":46.74,"endTime":48.753,"body":"But why is it cold in the first place?"},{"startTime":49.869,"endTime":52.71,"body":"And it really is very cold."},{"startTime":52.71,"endTime":55.71,"body":"If we look at a section"},{"startTime":52.71,"endTime":55.71,"body":"through the Atlantic,"},{"startTime":55.71,"endTime":58.923,"body":"so this is a sort of south to"},{"startTime":55.71,"endTime":58.923,"body":"north section in the Atlantic,"},{"startTime":60.0,"endTime":62.58,"body":"you can see that over most of the depth,"},{"startTime":62.58,"endTime":66.36,"body":"so it's about, on average"},{"startTime":62.58,"endTime":66.36,"body":"about four kilometers deep."},{"startTime":66.36,"endTime":68.76,"body":"So this is, remember this"},{"startTime":66.36,"endTime":68.76,"body":"has been exaggerated,"},{"startTime":68.76,"endTime":70.83,"body":"by about a factor of a"},{"startTime":68.76,"endTime":70.83,"body":"thousand in the vertical."},{"startTime":70.83,"endTime":72.66,"body":"If I showed you this to scale,"},{"startTime":72.66,"endTime":75.24,"body":"it would just be a straight"},{"startTime":72.66,"endTime":75.24,"body":"line on the screen."},{"startTime":75.24,"endTime":78.21,"body":"I tried to do that but it"},{"startTime":75.24,"endTime":78.21,"body":"was rather disappointing."},{"startTime":78.21,"endTime":83.07,"body":"So this scale is 12,000 kilometers."},{"startTime":83.07,"endTime":86.13,"body":"So if we look in the tropical Atlantic,"},{"startTime":86.13,"endTime":88.98,"body":"around here over a few hundred meters,"},{"startTime":88.98,"endTime":91.326,"body":"you go from surface temperatures,"},{"startTime":91.326,"endTime":95.4,"body":"getting on for 30 degrees,"},{"startTime":91.326,"endTime":95.4,"body":"bath temperature almost,"},{"startTime":95.4,"endTime":97.08,"body":"you go a few hundred meters down"},{"startTime":97.08,"endTime":100.29,"body":"and you reach temperatures"},{"startTime":97.08,"endTime":100.29,"body":"that you'd have to travel,"},{"startTime":100.29,"endTime":104.61,"body":"thousands and thousands of"},{"startTime":100.29,"endTime":104.61,"body":"kilometers north to find them."},{"startTime":104.61,"endTime":107.01,"body":"So we have this massive contrast,"},{"startTime":107.01,"endTime":110.07,"body":"in the rate at which temperatures"},{"startTime":107.01,"endTime":110.07,"body":"change in the vertical"},{"startTime":110.07,"endTime":112.56,"body":"and how they change in the horizontal."},{"startTime":112.56,"endTime":115.47,"body":"And it's even more extreme in the Pacific."},{"startTime":115.47,"endTime":119.163,"body":"Most of the Pacific is almost"},{"startTime":115.47,"endTime":119.163,"body":"at freezing temperature."},{"startTime":120.27,"endTime":122.19,"body":"You see, this is all this purple color,"},{"startTime":122.19,"endTime":125.43,"body":"that's down near zero degrees."},{"startTime":125.43,"endTime":128.37,"body":"And you know, in this some"},{"startTime":125.43,"endTime":128.37,"body":"parts of the tropical Pacific,"},{"startTime":128.37,"endTime":132.36,"body":"you actually if you were"},{"startTime":128.37,"endTime":132.36,"body":"in scuba diving depth,"},{"startTime":132.36,"endTime":134.52,"body":"so in the sort of depth you can get to,"},{"startTime":134.52,"endTime":136.95,"body":"with just a sort of regular air tank,"},{"startTime":136.95,"endTime":138.87,"body":"you could actually die of hypothermia,"},{"startTime":138.87,"endTime":141.36,"body":"before you're not this is recommended,"},{"startTime":141.36,"endTime":145.391,"body":"before you die of the bends, so to speak."},{"startTime":145.391,"endTime":148.5,"body":"Because the temperature"},{"startTime":145.391,"endTime":148.5,"body":"contrasts are so great,"},{"startTime":148.5,"endTime":150.39,"body":"in the vertical, so be careful,"},{"startTime":150.39,"endTime":152.19,"body":"when you're scuba diving off Hawaii."},{"startTime":154.14,"endTime":155.37,"body":"So why is this?"},{"startTime":155.37,"endTime":159.847,"body":"By the way, I'm just going"},{"startTime":155.37,"endTime":159.847,"body":"back to this profile,"},{"startTime":159.847,"endTime":161.34,"body":"you know, you might think,"},{"startTime":161.34,"endTime":163.14,"body":"well it's cold because"},{"startTime":161.34,"endTime":163.14,"body":"it can't be heated up."},{"startTime":163.14,"endTime":164.915,"body":"Well, that's a sort of very,"},{"startTime":164.915,"endTime":167.52,"body":"you know, if you don't mind me saying,"},{"startTime":167.52,"endTime":171.03,"body":"so that's a bit of an"},{"startTime":167.52,"endTime":171.03,"body":"Aristotelian way of thinking."},{"startTime":171.03,"endTime":172.92,"body":"Aristotle was convinced,"},{"startTime":172.92,"endTime":175.02,"body":"that everything had a"},{"startTime":172.92,"endTime":175.02,"body":"sort of natural state."},{"startTime":175.02,"endTime":178.35,"body":"Aristotle was a Greek"},{"startTime":175.02,"endTime":178.35,"body":"philosopher, scientist."},{"startTime":178.35,"endTime":181.02,"body":"Much of science, people call philosophy,"},{"startTime":181.02,"endTime":183.57,"body":"lots of, you know, footnotes to Plato."},{"startTime":183.57,"endTime":187.35,"body":"Science is largely tidying"},{"startTime":183.57,"endTime":187.35,"body":"up Aristotle's mistakes."},{"startTime":187.35,"endTime":189.45,"body":"So one of Aristotle's big mistakes was,"},{"startTime":189.45,"endTime":191.16,"body":"he thought everything had a natural state."},{"startTime":191.16,"endTime":195.18,"body":"So the natural state of"},{"startTime":191.16,"endTime":195.18,"body":"a cart was stationary"},{"startTime":195.18,"endTime":197.19,"body":"or the natural state of"},{"startTime":195.18,"endTime":197.19,"body":"any object was stationary"},{"startTime":197.19,"endTime":200.01,"body":"and you had to keep pushing"},{"startTime":197.19,"endTime":200.01,"body":"it to keep it going."},{"startTime":200.01,"endTime":200.843,"body":"Which meant, of course,"},{"startTime":200.843,"endTime":203.7,"body":"Aristotle could never understand"},{"startTime":200.843,"endTime":203.7,"body":"how the planets moved,"},{"startTime":203.7,"endTime":206.46,"body":"because he couldn't work"},{"startTime":203.7,"endTime":206.46,"body":"out what pushed them."},{"startTime":206.46,"endTime":209.46,"body":"Of course, Galileo"},{"startTime":206.46,"endTime":209.46,"body":"quite a few years later,"},{"startTime":209.46,"endTime":211.543,"body":"worked out that actually the"},{"startTime":209.46,"endTime":211.543,"body":"natural state of something,"},{"startTime":211.543,"endTime":214.59,"body":"was just to keep going"},{"startTime":211.543,"endTime":214.59,"body":"in whatever it was doing."},{"startTime":214.59,"endTime":216.06,"body":"And the same, you know,"},{"startTime":216.06,"endTime":218.25,"body":"unless there's something to slow it down."},{"startTime":218.25,"endTime":219.95,"body":"And the same goes for temperature."},{"startTime":220.86,"endTime":224.31,"body":"The natural state of water is not cold."},{"startTime":224.31,"endTime":226.71,"body":"If it's insulated, the"},{"startTime":224.31,"endTime":226.71,"body":"natural state of water,"},{"startTime":226.71,"endTime":229.65,"body":"is just to stay whatever"},{"startTime":226.71,"endTime":229.65,"body":"temperature it's at."},{"startTime":229.65,"endTime":232.26,"body":"So why is it at this"},{"startTime":229.65,"endTime":232.26,"body":"temperature in the first place?"},{"startTime":232.26,"endTime":236.19,"body":"And I mean, by the way, water"},{"startTime":232.26,"endTime":236.19,"body":"conducts heat as you know,"},{"startTime":236.19,"endTime":239.603,"body":"I mean, if you've ever"},{"startTime":236.19,"endTime":239.603,"body":"got soaked from the rain,"},{"startTime":239.603,"endTime":241.41,"body":"you'll feel that."},{"startTime":241.41,"endTime":244.17,"body":"It's actually one of the"},{"startTime":241.41,"endTime":244.17,"body":"best conductors of heat,"},{"startTime":244.17,"endTime":247.56,"body":"that's not a metal, that's out there."},{"startTime":247.56,"endTime":252.42,"body":"And so if you hold a nail in a gas flame,"},{"startTime":252.42,"endTime":253.59,"body":"again, not recommended,"},{"startTime":253.59,"endTime":258.067,"body":"but you'll notice the"},{"startTime":253.59,"endTime":258.067,"body":"temperature equilibrates,"},{"startTime":259.38,"endTime":262.29,"body":"you know, evens up along"},{"startTime":259.38,"endTime":262.29,"body":"the nail quite quickly."},{"startTime":262.29,"endTime":263.82,"body":"Within a a minute or two,"},{"startTime":263.82,"endTime":266.133,"body":"temperature will be"},{"startTime":263.82,"endTime":266.133,"body":"uniform along the nail."},{"startTime":267.06,"endTime":269.94,"body":"Water, I said it was one of"},{"startTime":267.06,"endTime":269.94,"body":"the best conductors of heat,"},{"startTime":269.94,"endTime":273.39,"body":"but it's not nearly as good as any metal."},{"startTime":273.39,"endTime":275.67,"body":"So if you take a glass of water,"},{"startTime":275.67,"endTime":278.25,"body":"just say 10 centimeters deep"},{"startTime":278.25,"endTime":280.38,"body":"or better still a styrofoam cup,"},{"startTime":280.38,"endTime":282.51,"body":"so you don't need to worry"},{"startTime":280.38,"endTime":282.51,"body":"about heat going down,"},{"startTime":282.51,"endTime":286.05,"body":"through the walls of the container."},{"startTime":286.05,"endTime":288.24,"body":"It actually would take several hours,"},{"startTime":288.24,"endTime":291.81,"body":"for you to warm it up by"},{"startTime":288.24,"endTime":291.81,"body":"conduction from the surface."},{"startTime":291.81,"endTime":294.0,"body":"So that's the contrast between,"},{"startTime":294.0,"endTime":296.52,"body":"you know, a metal object like a nail"},{"startTime":296.52,"endTime":300.42,"body":"and liquid water, even though"},{"startTime":296.52,"endTime":300.42,"body":"water does conduct heat."},{"startTime":300.42,"endTime":304.11,"body":"But if you, by the way,"},{"startTime":304.11,"endTime":309.11,"body":"the depth which temperatures"},{"startTime":304.11,"endTime":309.11,"body":"penetrate by conduction,"},{"startTime":311.01,"endTime":313.74,"body":"the speed, the length of time it takes,"},{"startTime":313.74,"endTime":315.57,"body":"for you know, a warming at the surface,"},{"startTime":315.57,"endTime":317.94,"body":"to penetrate down by conduction,"},{"startTime":317.94,"endTime":322.5,"body":"goes with the square on the depth."},{"startTime":322.5,"endTime":324.66,"body":"And that's sort of"},{"startTime":322.5,"endTime":324.66,"body":"again, okay, most of you,"},{"startTime":324.66,"endTime":326.43,"body":"before you sort of start,"},{"startTime":324.66,"endTime":326.43,"body":"he's moving into maths,"},{"startTime":326.43,"endTime":328.44,"body":"I'm going to tune out at this point,"},{"startTime":328.44,"endTime":330.54,"body":"that should be fairly"},{"startTime":328.44,"endTime":330.54,"body":"obvious to you anyway,"},{"startTime":330.54,"endTime":335.54,"body":"because what's driving heat along the nail"},{"startTime":336.42,"endTime":339.81,"body":"or down through the glass"},{"startTime":336.42,"endTime":339.81,"body":"of water is the gradient,"},{"startTime":339.81,"endTime":343.47,"body":"is how fast the temperature is changing,"},{"startTime":343.47,"endTime":345.21,"body":"either in the vertical"},{"startTime":343.47,"endTime":345.21,"body":"in the glass of water"},{"startTime":345.21,"endTime":347.01,"body":"or along the nail."},{"startTime":347.01,"endTime":350.01,"body":"And the further you go,"},{"startTime":350.01,"endTime":355.01,"body":"the less the average temperature"},{"startTime":350.01,"endTime":355.01,"body":"contrast per unit length,"},{"startTime":355.2,"endTime":357.06,"body":"the less rapidly temperatures change."},{"startTime":357.06,"endTime":360.66,"body":"So the slower it moves heat along."},{"startTime":360.66,"endTime":362.22,"body":"So you can just,"},{"startTime":362.22,"endTime":363.96,"body":"you can do the sum in"},{"startTime":362.22,"endTime":363.96,"body":"your head if you want."},{"startTime":363.96,"endTime":366.36,"body":"If I tell you that it takes several hours,"},{"startTime":366.36,"endTime":369.69,"body":"for a glass of water in a 10 centimeters"},{"startTime":369.69,"endTime":371.61,"body":"or styrofoam cup of water,"},{"startTime":371.61,"endTime":373.59,"body":"to equilibrate temperature,"},{"startTime":373.59,"endTime":378.59,"body":"it would take several"},{"startTime":373.59,"endTime":378.59,"body":"thousand years for conduction,"},{"startTime":378.72,"endTime":380.82,"body":"to get down through, you know,"},{"startTime":380.82,"endTime":383.763,"body":"even just several hundred meters of water."},{"startTime":384.9,"endTime":385.89,"body":"So then you're like, oh wait a minute."},{"startTime":385.89,"endTime":386.85,"body":"Several thousand years ago?"},{"startTime":386.85,"endTime":390.48,"body":"Well 20,000 years ago, the"},{"startTime":386.85,"endTime":390.48,"body":"earth was in an Ice Age."},{"startTime":390.48,"endTime":392.73,"body":"Maybe this is because of the Ice Age."},{"startTime":392.73,"endTime":394.77,"body":"Okay, it's not, okay?"},{"startTime":394.77,"endTime":397.74,"body":"'Cause of course, if you go"},{"startTime":394.77,"endTime":397.74,"body":"that route, you might think,"},{"startTime":397.74,"endTime":398.85,"body":"maybe sea level rises,"},{"startTime":398.85,"endTime":400.2,"body":"all the recovery from the last Ice Age."},{"startTime":400.2,"endTime":402.03,"body":"And then I remember in the last lecture,"},{"startTime":402.03,"endTime":403.59,"body":"I commented on the number of people,"},{"startTime":403.59,"endTime":405.18,"body":"who write like to write me angry emails,"},{"startTime":405.18,"endTime":406.68,"body":"telling me that they've"},{"startTime":405.18,"endTime":406.68,"body":"discovered that climate change,"},{"startTime":406.68,"endTime":408.54,"body":"is entirely natural."},{"startTime":408.54,"endTime":413.458,"body":"So no, that's not the reason"},{"startTime":408.54,"endTime":413.458,"body":"that deep oceans are cold."},{"startTime":413.458,"endTime":416.94,"body":"Because even back in the Ice Age,"},{"startTime":416.94,"endTime":418.56,"body":"surface temperatures in the Tropics,"},{"startTime":418.56,"endTime":420.78,"body":"are only a few degrees"},{"startTime":418.56,"endTime":420.78,"body":"colder than they are now."},{"startTime":420.78,"endTime":423.9,"body":"Certainly not that kind"},{"startTime":420.78,"endTime":423.9,"body":"of temperature contrast."},{"startTime":423.9,"endTime":426.66,"body":"So and you know, the ocean's been around,"},{"startTime":426.66,"endTime":428.319,"body":"for billions of years."},{"startTime":428.319,"endTime":432.15,"body":"I'm hoping by now you should"},{"startTime":428.319,"endTime":432.15,"body":"be a little bit puzzled,"},{"startTime":432.15,"endTime":434.643,"body":"why is the deep ocean so cold?"},{"startTime":435.74,"endTime":438.513,"body":"'Cause even just conduction"},{"startTime":435.74,"endTime":438.513,"body":"would warm it up."},{"startTime":439.441,"endTime":444.441,"body":"And the answer is a very"},{"startTime":439.441,"endTime":444.441,"body":"sort of important one,"},{"startTime":444.673,"endTime":447.783,"body":"a very important one"},{"startTime":444.673,"endTime":447.783,"body":"for our net zero story."},{"startTime":448.77,"endTime":450.189,"body":"I hope you've all,"},{"startTime":450.189,"endTime":452.61,"body":"you know, I'm sure you're all aware,"},{"startTime":452.61,"endTime":454.44,"body":"that temperature is not the only effect,"},{"startTime":454.44,"endTime":457.823,"body":"the factor that affects"},{"startTime":454.44,"endTime":457.823,"body":"the density of seawater."},{"startTime":457.823,"endTime":459.537,"body":"Any idea where this is?"},{"startTime":459.537,"endTime":464.095,"body":"The sort of hint is, I"},{"startTime":459.537,"endTime":464.095,"body":"guess, also in the newspaper."},{"startTime":464.095,"endTime":466.23,"body":"That's the Dead Sea."},{"startTime":466.23,"endTime":467.73,"body":"This is somebody doing the classic thing,"},{"startTime":467.73,"endTime":468.9,"body":"of reading a newspaper in the Dead Sea."},{"startTime":468.9,"endTime":473.9,"body":"If you have enough salt"},{"startTime":468.9,"endTime":473.9,"body":"in water, it's very dense."},{"startTime":474.09,"endTime":477.9,"body":"And, you know, as another much,"},{"startTime":477.9,"endTime":481.11,"body":"much better scientist than Aristotle,"},{"startTime":481.11,"endTime":482.4,"body":"as Archimedes point out,"},{"startTime":482.4,"endTime":486.78,"body":"that means that you can"},{"startTime":482.4,"endTime":486.78,"body":"float in it at high enough,"},{"startTime":486.78,"endTime":488.971,"body":"that you can actually read a newspaper."},{"startTime":488.971,"endTime":493.971,"body":"So the salt content of"},{"startTime":488.971,"endTime":493.971,"body":"water increases its density."},{"startTime":494.78,"endTime":498.483,"body":"So if you want to increase"},{"startTime":494.78,"endTime":498.483,"body":"the density of water,"},{"startTime":499.461,"endTime":503.46,"body":"so these lines show you"},{"startTime":499.461,"endTime":503.46,"body":"lines, contours of density,"},{"startTime":503.46,"endTime":505.83,"body":"it gets more dense in this direction."},{"startTime":505.83,"endTime":510.51,"body":"You can either cool the water"},{"startTime":505.83,"endTime":510.51,"body":"or you can make it saltier."},{"startTime":510.51,"endTime":515.16,"body":"So both of these things"},{"startTime":510.51,"endTime":515.16,"body":"make sea water denser."},{"startTime":515.16,"endTime":519.24,"body":"So cooling, for example, you know,"},{"startTime":519.24,"endTime":521.04,"body":"the wind blowing over"},{"startTime":519.24,"endTime":521.04,"body":"the surface of the ocean,"},{"startTime":521.04,"endTime":523.92,"body":"cooling it down, that"},{"startTime":521.04,"endTime":523.92,"body":"helps make water denser."},{"startTime":523.92,"endTime":527.46,"body":"But evaporation and the formation of ice,"},{"startTime":527.46,"endTime":530.25,"body":"that also makes water saltier."},{"startTime":530.25,"endTime":535.25,"body":"When ice forms, the salt is left behind."},{"startTime":535.98,"endTime":538.263,"body":"So if you're ever stuck on an ice floe,"},{"startTime":539.79,"endTime":542.85,"body":"lots of survival tips in this lecture,"},{"startTime":542.85,"endTime":545.43,"body":"eat the ice, don't drink the sea water."},{"startTime":545.43,"endTime":546.263,"body":"Yep?"},{"startTime":546.263,"endTime":548.07,"body":"Because it's much fresher."},{"startTime":548.07,"endTime":550.773,"body":"But what happens is, as seawater freezes,"},{"startTime":552.711,"endTime":555.03,"body":"the water that's left behind,"},{"startTime":555.03,"endTime":558.3,"body":"it becomes saltier and therefore denser."},{"startTime":558.3,"endTime":560.43,"body":"So there you are."},{"startTime":560.43,"endTime":563.82,"body":"Here's water getting, you"},{"startTime":560.43,"endTime":563.82,"body":"know, as you increase,"},{"startTime":563.82,"endTime":567.39,"body":"reduce temperature and"},{"startTime":563.82,"endTime":567.39,"body":"increase the salt content,"},{"startTime":567.39,"endTime":569.31,"body":"the water gets denser."},{"startTime":569.31,"endTime":574.11,"body":"And so the places where water can escape,"},{"startTime":574.11,"endTime":575.79,"body":"to the ocean depths,"},{"startTime":575.79,"endTime":578.88,"body":"are places where it's"},{"startTime":575.79,"endTime":578.88,"body":"very dense at the surface,"},{"startTime":578.88,"endTime":580.29,"body":"to start with."},{"startTime":580.29,"endTime":583.44,"body":"And those are places where it's very cold"},{"startTime":583.44,"endTime":586.62,"body":"and where the formation of ice"},{"startTime":586.62,"endTime":589.26,"body":"and the action of wind"},{"startTime":586.62,"endTime":589.26,"body":"blowing over the ocean,"},{"startTime":589.26,"endTime":592.68,"body":"act to make water particularly dense."},{"startTime":592.68,"endTime":594.84,"body":"So places like this, that's"},{"startTime":592.68,"endTime":594.84,"body":"ice floe in the background,"},{"startTime":594.84,"endTime":596.85,"body":"to give you a hint about where you are."},{"startTime":596.85,"endTime":599.4,"body":"You got the wind, a storm"},{"startTime":596.85,"endTime":599.4,"body":"in the North Atlantic,"},{"startTime":599.4,"endTime":602.233,"body":"causing lots of"},{"startTime":599.4,"endTime":602.233,"body":"evaporation, lots of spray."},{"startTime":602.233,"endTime":606.03,"body":"The water that's left"},{"startTime":602.233,"endTime":606.03,"body":"behind is getting saltier."},{"startTime":606.03,"endTime":609.24,"body":"Ice is forming, that's also"},{"startTime":606.03,"endTime":609.24,"body":"making the water saltier."},{"startTime":609.24,"endTime":612.783,"body":"Eventually, that surface"},{"startTime":609.24,"endTime":612.783,"body":"water becomes denser,"},{"startTime":612.783,"endTime":615.0,"body":"than the water beneath it"},{"startTime":615.0,"endTime":617.913,"body":"and slides away down"},{"startTime":615.0,"endTime":617.913,"body":"into the ocean depths."},{"startTime":619.44,"endTime":622.953,"body":"Now crucially, once the"},{"startTime":619.44,"endTime":622.953,"body":"water's left the surface,"},{"startTime":624.03,"endTime":626.38,"body":"there's nothing down"},{"startTime":624.03,"endTime":626.38,"body":"there to warm it up again."},{"startTime":627.3,"endTime":630.69,"body":"There's no equivalent to rain formation"},{"startTime":630.69,"endTime":634.759,"body":"or sun in the atmosphere"},{"startTime":630.69,"endTime":634.759,"body":"to warm up different,"},{"startTime":634.759,"endTime":637.713,"body":"it's on its own."},{"startTime":638.73,"endTime":641.04,"body":"There's nothing happening down there."},{"startTime":641.04,"endTime":643.653,"body":"So, once it's gone,"},{"startTime":645.21,"endTime":648.87,"body":"ocean water remembers the temperature"},{"startTime":648.87,"endTime":651.63,"body":"and the salt content it had,"},{"startTime":651.63,"endTime":653.61,"body":"when it was last at the surface,"},{"startTime":653.61,"endTime":655.95,"body":"until it gets back to the surface again,"},{"startTime":655.95,"endTime":658.05,"body":"which may be many, many hundreds of years."},{"startTime":658.98,"endTime":663.98,"body":"So water forms in these isolated regions."},{"startTime":664.02,"endTime":665.22,"body":"So here they are."},{"startTime":665.22,"endTime":666.66,"body":"There's a few regions."},{"startTime":666.66,"endTime":670.32,"body":"The Labrador Sea, the"},{"startTime":666.66,"endTime":670.32,"body":"extreme North Atlantic"},{"startTime":670.32,"endTime":672.9,"body":"and this region near Antarctica,"},{"startTime":672.9,"endTime":675.03,"body":"where the water's cold enough,"},{"startTime":675.03,"endTime":677.97,"body":"to escape down into the ocean depths."},{"startTime":677.97,"endTime":681.24,"body":"So all of the water that you see,"},{"startTime":681.24,"endTime":684.93,"body":"in 90% of the world's"},{"startTime":681.24,"endTime":684.93,"body":"oceans has got there,"},{"startTime":684.93,"endTime":688.293,"body":"through the so-called deep"},{"startTime":684.93,"endTime":688.293,"body":"water formation regions."},{"startTime":689.16,"endTime":692.49,"body":"So it really is arctic temperatures,"},{"startTime":692.49,"endTime":695.01,"body":"below the tropical Pacific,"},{"startTime":695.01,"endTime":698.49,"body":"just a few, you know,"},{"startTime":695.01,"endTime":698.49,"body":"50 to 100 meters down."},{"startTime":698.49,"endTime":702.63,"body":"You find arctic temperatures"},{"startTime":698.49,"endTime":702.63,"body":"because it's arctic water."},{"startTime":702.63,"endTime":704.223,"body":"It's come from the Arctic."},{"startTime":705.33,"endTime":707.61,"body":"Because once it's down there,"},{"startTime":707.61,"endTime":709.95,"body":"it can't mix with the water above it,"},{"startTime":709.95,"endTime":712.47,"body":"because it's so cold and dense"},{"startTime":712.47,"endTime":714.75,"body":"and the water above it is"},{"startTime":712.47,"endTime":714.75,"body":"being heated by the sun"},{"startTime":714.75,"endTime":718.41,"body":"and made, you know, made"},{"startTime":714.75,"endTime":718.41,"body":"less dense as a result"},{"startTime":718.41,"endTime":719.97,"body":"and sits on top."},{"startTime":719.97,"endTime":724.11,"body":"So here's an amazing"},{"startTime":719.97,"endTime":724.11,"body":"graphic courtesy of NASA,"},{"startTime":724.11,"endTime":726.63,"body":"which shows you this circulation."},{"startTime":726.63,"endTime":729.51,"body":"Do you see the water flowing"},{"startTime":726.63,"endTime":729.51,"body":"up through the North Atlantic"},{"startTime":729.51,"endTime":731.1,"body":"and reaching this black region,"},{"startTime":731.1,"endTime":733.02,"body":"that color indicates the density."},{"startTime":733.02,"endTime":736.56,"body":"And in this region where surface"},{"startTime":733.02,"endTime":736.56,"body":"density is at its highest,"},{"startTime":736.56,"endTime":739.65,"body":"the water drops away down"},{"startTime":736.56,"endTime":739.65,"body":"into the ocean depths"},{"startTime":739.65,"endTime":742.83,"body":"and then it can't mix with"},{"startTime":739.65,"endTime":742.83,"body":"the water above it anymore,"},{"startTime":742.83,"endTime":745.11,"body":"because it's so dense,"},{"startTime":742.83,"endTime":745.11,"body":"it's stuck down there."},{"startTime":745.11,"endTime":747.99,"body":"And it travels southwards on average,"},{"startTime":747.99,"endTime":749.88,"body":"back through all these sea mountains."},{"startTime":749.88,"endTime":752.34,"body":"Remember this is massively"},{"startTime":749.88,"endTime":752.34,"body":"exaggerated in the verticals,"},{"startTime":752.34,"endTime":755.55,"body":"so it's not nearly that spiky in reality."},{"startTime":755.55,"endTime":757.707,"body":"And you can see that this downward,"},{"startTime":757.707,"endTime":761.85,"body":"under surface deep, deep flow,"},{"startTime":761.85,"endTime":764.76,"body":"coming back down through"},{"startTime":761.85,"endTime":764.76,"body":"past the tropical Atlantic,"},{"startTime":764.76,"endTime":766.05,"body":"no mixing with the surface,"},{"startTime":766.05,"endTime":768.51,"body":"because you've got this density contrast,"},{"startTime":768.51,"endTime":771.702,"body":"the lighter, less dense water above,"},{"startTime":771.702,"endTime":773.16,"body":"more dense water below."},{"startTime":773.16,"endTime":775.23,"body":"And goes all the way around the world,"},{"startTime":775.23,"endTime":778.2,"body":"back out into the Pacific."},{"startTime":778.2,"endTime":783.2,"body":"And then eventually,"},{"startTime":778.2,"endTime":783.2,"body":"somewhere else in the oceans,"},{"startTime":783.45,"endTime":786.27,"body":"it resurfaces again."},{"startTime":786.27,"endTime":788.04,"body":"It's a fantastic graphic."},{"startTime":788.04,"endTime":789.93,"body":"The only thing I don't like about it,"},{"startTime":789.93,"endTime":791.31,"body":"is that it sort of implies,"},{"startTime":791.31,"endTime":795.03,"body":"you see here the water sort"},{"startTime":791.31,"endTime":795.03,"body":"of popping up at one place."},{"startTime":795.03,"endTime":796.35,"body":"That's actually very misleading."},{"startTime":796.35,"endTime":798.347,"body":"That's not the way the ocean works."},{"startTime":798.347,"endTime":802.68,"body":"There's these few places"},{"startTime":798.347,"endTime":802.68,"body":"where deep water is formed,"},{"startTime":802.68,"endTime":803.513,"body":"but there's no such thing,"},{"startTime":803.513,"endTime":805.89,"body":"as a shallow water formation region."},{"startTime":805.89,"endTime":809.73,"body":"It's actually much more"},{"startTime":805.89,"endTime":809.73,"body":"like an aquarium pump,"},{"startTime":809.73,"endTime":811.08,"body":"but working in reverse."},{"startTime":811.08,"endTime":813.93,"body":"So if you've got a tropical aquarium,"},{"startTime":813.93,"endTime":816.69,"body":"you know you've got to have"},{"startTime":813.93,"endTime":816.69,"body":"this sort of pump thing,"},{"startTime":816.69,"endTime":818.13,"body":"that sort of circulates the water,"},{"startTime":818.13,"endTime":820.89,"body":"pulls water from the bottom"},{"startTime":818.13,"endTime":820.89,"body":"and pushes it out at the top."},{"startTime":820.89,"endTime":822.78,"body":"And so over the rest of the aquarium,"},{"startTime":822.78,"endTime":826.8,"body":"you've got a very, very"},{"startTime":822.78,"endTime":826.8,"body":"gradual down-welling of water."},{"startTime":826.8,"endTime":828.3,"body":"And then you've got this one little pipe,"},{"startTime":828.3,"endTime":830.31,"body":"pumping it back up to the surface."},{"startTime":830.31,"endTime":833.13,"body":"Well the oceans work in exactly"},{"startTime":830.31,"endTime":833.13,"body":"the same way in reverse."},{"startTime":833.13,"endTime":835.17,"body":"You've got these few points,"},{"startTime":835.17,"endTime":836.73,"body":"where you've effectively got a pipe,"},{"startTime":836.73,"endTime":838.89,"body":"from the surface down to the deep ocean."},{"startTime":838.89,"endTime":840.6,"body":"And then over the rest of the ocean,"},{"startTime":840.6,"endTime":844.17,"body":"it's slowly up-welling, yep?"},{"startTime":844.17,"endTime":847.11,"body":"That's the only criticism"},{"startTime":844.17,"endTime":847.11,"body":"I've got of this,"},{"startTime":847.11,"endTime":850.47,"body":"otherwise fantastic animation from NASA."},{"startTime":850.47,"endTime":853.26,"body":"Anyway, I think that's all"},{"startTime":850.47,"endTime":853.26,"body":"that's really interesting,"},{"startTime":853.26,"endTime":855.12,"body":"about just the way the ocean works."},{"startTime":855.12,"endTime":857.52,"body":"But what has it got to do with net zero?"},{"startTime":857.52,"endTime":860.61,"body":"Well, it helps us understand,"},{"startTime":860.61,"endTime":863.88,"body":"where energy goes in the climate system."},{"startTime":863.88,"endTime":866.048,"body":"Now remember from the previous lecture"},{"startTime":866.048,"endTime":868.05,"body":"and we had a sort of 10 minute recap,"},{"startTime":868.05,"endTime":869.13,"body":"before this lecture started,"},{"startTime":869.13,"endTime":871.05,"body":"for those who weren't there,"},{"startTime":871.05,"endTime":873.54,"body":"we emphasized that our climate system,"},{"startTime":873.54,"endTime":875.94,"body":"is fundamentally governed"},{"startTime":873.54,"endTime":875.94,"body":"by this flow of energy,"},{"startTime":875.94,"endTime":879.75,"body":"in from the sun and the flow"},{"startTime":875.94,"endTime":879.75,"body":"of energy back out into space."},{"startTime":879.75,"endTime":881.61,"body":"A little bit like a bathtub."},{"startTime":881.61,"endTime":885.84,"body":"If you crank up the tap and"},{"startTime":881.61,"endTime":885.84,"body":"increase the flow of energy in,"},{"startTime":885.84,"endTime":888.78,"body":"if this is a sort of the"},{"startTime":885.84,"endTime":888.78,"body":"plug hole of the bath,"},{"startTime":888.78,"endTime":893.78,"body":"then the heat content of the"},{"startTime":888.78,"endTime":893.78,"body":"climate system increases,"},{"startTime":894.48,"endTime":897.84,"body":"until the pressure driving energy out,"},{"startTime":897.84,"endTime":900.3,"body":"balances the pressure"},{"startTime":897.84,"endTime":900.3,"body":"of the energy coming in."},{"startTime":900.3,"endTime":902.34,"body":"And we sort of demonstrated"},{"startTime":900.3,"endTime":902.34,"body":"that with that,"},{"startTime":902.34,"endTime":905.133,"body":"with our gadget, which"},{"startTime":902.34,"endTime":905.133,"body":"we'll come to in a minute."},{"startTime":906.06,"endTime":910.53,"body":"So where we are now is"},{"startTime":906.06,"endTime":910.53,"body":"we're adding energy,"},{"startTime":910.53,"endTime":912.54,"body":"to the climate system,"},{"startTime":912.54,"endTime":915.603,"body":"because of the increase"},{"startTime":912.54,"endTime":915.603,"body":"in greenhouse gases,"},{"startTime":917.64,"endTime":921.15,"body":"over the past century and a half or so."},{"startTime":921.15,"endTime":924.0,"body":"At about two and a half"},{"startTime":921.15,"endTime":924.0,"body":"watts per square meter,"},{"startTime":924.0,"endTime":925.92,"body":"added up over the whole earth surface,"},{"startTime":925.92,"endTime":927.786,"body":"which adds up to a lot of energy."},{"startTime":927.786,"endTime":930.72,"body":"And because the world's already warmed up,"},{"startTime":930.72,"endTime":935.04,"body":"about one and three quarters"},{"startTime":930.72,"endTime":935.04,"body":"is going back out into space."},{"startTime":935.04,"endTime":936.6,"body":"And the difference"},{"startTime":935.04,"endTime":936.6,"body":"between those two numbers,"},{"startTime":936.6,"endTime":938.103,"body":"is three quarters."},{"startTime":938.103,"endTime":940.903,"body":"The maths in this lecture is"},{"startTime":938.103,"endTime":940.903,"body":"all really straightforward."},{"startTime":941.85,"endTime":946.85,"body":"And so the world is warming"},{"startTime":941.85,"endTime":946.85,"body":"up by that much energy,"},{"startTime":950.46,"endTime":952.65,"body":"you know, that's per square meter,"},{"startTime":952.65,"endTime":954.36,"body":"of the earth's surface we're seeing."},{"startTime":954.36,"endTime":957.45,"body":"But that doesn't tell you itself,"},{"startTime":957.45,"endTime":960.03,"body":"how fast the temperatures are going up."},{"startTime":960.03,"endTime":963.09,"body":"I'm telling you how"},{"startTime":960.03,"endTime":963.09,"body":"fast the energy content,"},{"startTime":963.09,"endTime":964.92,"body":"of the climate system is going up."},{"startTime":964.92,"endTime":968.283,"body":"But what does that mean"},{"startTime":964.92,"endTime":968.283,"body":"for surface warming?"},{"startTime":969.12,"endTime":972.27,"body":"And to understand that,"},{"startTime":969.12,"endTime":972.27,"body":"you need to understand,"},{"startTime":972.27,"endTime":974.16,"body":"where the energy's going,"},{"startTime":974.16,"endTime":977.493,"body":"how it's distributed"},{"startTime":974.16,"endTime":977.493,"body":"around the climate system."},{"startTime":979.17,"endTime":984.03,"body":"So this is a graph of"},{"startTime":979.17,"endTime":984.03,"body":"where energy has gone,"},{"startTime":984.03,"endTime":986.973,"body":"in the climate system since 1960s."},{"startTime":986.973,"endTime":991.47,"body":"1960 here, to the present of 2018 or so."},{"startTime":991.47,"endTime":994.47,"body":"And this just shows you how heat energy,"},{"startTime":994.47,"endTime":996.583,"body":"has accumulated in the climate system."},{"startTime":996.583,"endTime":1000.05,"body":"And one of the sort of"},{"startTime":996.583,"endTime":1000.05,"body":"most impressive things,"},{"startTime":1000.05,"endTime":1004.25,"body":"about this figure is this"},{"startTime":1000.05,"endTime":1004.25,"body":"fine red line you see here,"},{"startTime":1004.25,"endTime":1007.1,"body":"which shows, when we use satellites,"},{"startTime":1007.1,"endTime":1010.73,"body":"to work out how much energy,"},{"startTime":1010.73,"endTime":1013.932,"body":"is being taken up by the climate system,"},{"startTime":1013.932,"endTime":1017.688,"body":"as a whole every year"},{"startTime":1017.688,"endTime":1021.95,"body":"and then compare that to"},{"startTime":1017.688,"endTime":1021.95,"body":"where measuring the oceans"},{"startTime":1021.95,"endTime":1025.1,"body":"and the land and the ice"},{"startTime":1021.95,"endTime":1025.1,"body":"caps, where energy's gone,"},{"startTime":1025.1,"endTime":1027.14,"body":"we get a very good match."},{"startTime":1027.14,"endTime":1031.31,"body":"You see how this red line"},{"startTime":1027.14,"endTime":1031.31,"body":"matches the blue line very well."},{"startTime":1031.31,"endTime":1034.85,"body":"So we know where the energy is"},{"startTime":1031.31,"endTime":1034.85,"body":"going in the climate system."},{"startTime":1034.85,"endTime":1038.18,"body":"Which, you know, you think,"},{"startTime":1034.85,"endTime":1038.18,"body":"well how hard was that?"},{"startTime":1038.18,"endTime":1039.26,"body":"Really hard, okay?"},{"startTime":1039.26,"endTime":1041.39,"body":"Lots of people had to do"},{"startTime":1039.26,"endTime":1041.39,"body":"a lot of work to do that."},{"startTime":1041.39,"endTime":1044.66,"body":"But, you know, it's done."},{"startTime":1044.66,"endTime":1047.18,"body":"And it's lots of things like this."},{"startTime":1047.18,"endTime":1049.37,"body":"Because, of course, what we're doing here,"},{"startTime":1049.37,"endTime":1051.14,"body":"in order to work out"},{"startTime":1049.37,"endTime":1051.14,"body":"what the energy content,"},{"startTime":1051.14,"endTime":1053.0,"body":"this is the pale blue here,"},{"startTime":1053.0,"endTime":1056.06,"body":"is the top 300 meters of the oceans."},{"startTime":1056.06,"endTime":1059.06,"body":"The slightly darker blue"},{"startTime":1056.06,"endTime":1059.06,"body":"is the top 700 meters."},{"startTime":1059.06,"endTime":1060.69,"body":"And then darker still,"},{"startTime":1060.69,"endTime":1064.37,"body":"sorry, this is the top 300"},{"startTime":1060.69,"endTime":1064.37,"body":"meters above the green line."},{"startTime":1064.37,"endTime":1066.59,"body":"This is the top 700 and so on."},{"startTime":1066.59,"endTime":1070.97,"body":"So you can see how"},{"startTime":1066.59,"endTime":1070.97,"body":"these different regions,"},{"startTime":1070.97,"endTime":1074.27,"body":"are giving you different, you know,"},{"startTime":1074.27,"endTime":1078.26,"body":"how the energy is distributed"},{"startTime":1074.27,"endTime":1078.26,"body":"through the ocean system."},{"startTime":1078.26,"endTime":1081.26,"body":"And as a result of that, you see that,"},{"startTime":1081.26,"endTime":1085.753,"body":"you know, in order to just"},{"startTime":1081.26,"endTime":1085.753,"body":"be able to observe that,"},{"startTime":1088.31,"endTime":1091.25,"body":"we've had to instrument"},{"startTime":1088.31,"endTime":1091.25,"body":"up the earth oceans,"},{"startTime":1091.25,"endTime":1093.29,"body":"with vast numbers of drifting buoys,"},{"startTime":1093.29,"endTime":1095.66,"body":"to work out how fast"},{"startTime":1093.29,"endTime":1095.66,"body":"temperatures are going up,"},{"startTime":1095.66,"endTime":1096.68,"body":"in different regions."},{"startTime":1096.68,"endTime":1098.48,"body":"But this has been done and we can now,"},{"startTime":1098.48,"endTime":1101.78,"body":"there's a lot of uncertainty"},{"startTime":1098.48,"endTime":1101.78,"body":"sort of pre-1980s,"},{"startTime":1101.78,"endTime":1105.02,"body":"because we didn't have these"},{"startTime":1101.78,"endTime":1105.02,"body":"buoy networks back then,"},{"startTime":1105.02,"endTime":1106.67,"body":"but we've got it pretty well wired up now,"},{"startTime":1106.67,"endTime":1109.28,"body":"so we know where the energy's going."},{"startTime":1109.28,"endTime":1112.76,"body":"And this is what's accumulating"},{"startTime":1109.28,"endTime":1112.76,"body":"in the climate system."},{"startTime":1112.76,"endTime":1115.29,"body":"The unit here is something"},{"startTime":1112.76,"endTime":1115.29,"body":"called a zettajoule"},{"startTime":1116.6,"endTime":1118.64,"body":"and you've probably heard"},{"startTime":1116.6,"endTime":1118.64,"body":"of a joule of energy."},{"startTime":1118.64,"endTime":1121.43,"body":"That's the energy it takes to warm up,"},{"startTime":1121.43,"endTime":1123.17,"body":"a liter of water by one degree,"},{"startTime":1123.17,"endTime":1124.19,"body":"I think I've got that right"},{"startTime":1124.19,"endTime":1125.94,"body":"or kilogram of water by one degree."},{"startTime":1127.4,"endTime":1132.4,"body":"So a zettajoule is one"},{"startTime":1127.4,"endTime":1132.4,"body":"followed by 21 zeros joules."},{"startTime":1134.96,"endTime":1138.92,"body":"So it's a billion trillion joules."},{"startTime":1138.92,"endTime":1140.297,"body":"So quite a substantial number."},{"startTime":1140.297,"endTime":1142.16,"body":"If you want to compare that to,"},{"startTime":1142.16,"endTime":1145.25,"body":"so that's the 0.75 watts meter square."},{"startTime":1145.25,"endTime":1146.12,"body":"If you want to talk,"},{"startTime":1146.12,"endTime":1148.37,"body":"compare that to number you"},{"startTime":1146.12,"endTime":1148.37,"body":"might be more familiar with,"},{"startTime":1148.37,"endTime":1152.81,"body":"that's the total amount"},{"startTime":1148.37,"endTime":1152.81,"body":"of energy we generate,"},{"startTime":1152.81,"endTime":1154.19,"body":"mostly from burning fossil fuels,"},{"startTime":1154.19,"endTime":1156.8,"body":"but from hydropower and"},{"startTime":1154.19,"endTime":1156.8,"body":"everything else in the world,"},{"startTime":1156.8,"endTime":1157.883,"body":"over the same period."},{"startTime":1159.14,"endTime":1162.62,"body":"So the actual amount of energy we generate"},{"startTime":1162.62,"endTime":1165.02,"body":"and by the way, 75% of"},{"startTime":1162.62,"endTime":1165.02,"body":"that is wasted as well."},{"startTime":1165.02,"endTime":1166.85,"body":"So the actual energy we use,"},{"startTime":1166.85,"endTime":1169.16,"body":"will be quite a small"},{"startTime":1166.85,"endTime":1169.16,"body":"fraction of that, okay?"},{"startTime":1169.16,"endTime":1171.37,"body":"So that's whole of humanity,"},{"startTime":1171.37,"endTime":1175.46,"body":"compared to the energy"},{"startTime":1171.37,"endTime":1175.46,"body":"that's accumulating,"},{"startTime":1175.46,"endTime":1178.52,"body":"in the climate system as a"},{"startTime":1175.46,"endTime":1178.52,"body":"result of past emissions,"},{"startTime":1178.52,"endTime":1180.059,"body":"of greenhouse gases."},{"startTime":1180.059,"endTime":1182.03,"body":"So people often ask me, you know,"},{"startTime":1182.03,"endTime":1184.85,"body":"does it matter that a power station,"},{"startTime":1184.85,"endTime":1187.01,"body":"is generating heat itself"},{"startTime":1187.01,"endTime":1190.31,"body":"or that the steam coming"},{"startTime":1187.01,"endTime":1190.31,"body":"out of the cooling towers,"},{"startTime":1190.31,"endTime":1192.903,"body":"of a power station is quite hot."},{"startTime":1192.903,"endTime":1196.25,"body":"It is hot, it's steam."},{"startTime":1196.25,"endTime":1197.96,"body":"Is that what's causing global warming?"},{"startTime":1197.96,"endTime":1198.793,"body":"No."},{"startTime":1198.793,"endTime":1201.53,"body":"Because that energy is tiny,"},{"startTime":1201.53,"endTime":1204.35,"body":"compared to the energy"},{"startTime":1201.53,"endTime":1204.35,"body":"that's being trapped,"},{"startTime":1204.35,"endTime":1205.58,"body":"by those greenhouse gases,"},{"startTime":1205.58,"endTime":1207.53,"body":"that that power station"},{"startTime":1205.58,"endTime":1207.53,"body":"might have produced."},{"startTime":1207.53,"endTime":1210.95,"body":"That's the big impact on"},{"startTime":1207.53,"endTime":1210.95,"body":"energy in our climate system,"},{"startTime":1210.95,"endTime":1214.559,"body":"not the energy we actually"},{"startTime":1210.95,"endTime":1214.559,"body":"generate from burning stuff"},{"startTime":1214.559,"endTime":1216.05,"body":"Okay, by the way,"},{"startTime":1216.05,"endTime":1218.54,"body":"notice here there are some"},{"startTime":1216.05,"endTime":1218.54,"body":"extra stripes down here,"},{"startTime":1218.54,"endTime":1222.5,"body":"that the little beige one is"},{"startTime":1218.54,"endTime":1222.5,"body":"energy accumulating on land"},{"startTime":1222.5,"endTime":1225.44,"body":"and energy accumulating in ice,"},{"startTime":1225.44,"endTime":1228.62,"body":"mostly by melting ice"},{"startTime":1225.44,"endTime":1228.62,"body":"is the sort of gray one."},{"startTime":1228.62,"endTime":1232.67,"body":"And finally the purple one"},{"startTime":1228.62,"endTime":1232.67,"body":"is the tiny amount of energy,"},{"startTime":1232.67,"endTime":1235.22,"body":"that's accumulating in the atmosphere."},{"startTime":1235.22,"endTime":1238.01,"body":"And the reason that's quite"},{"startTime":1235.22,"endTime":1238.01,"body":"small compared to the ocean,"},{"startTime":1238.01,"endTime":1241.22,"body":"is that the atmosphere has"},{"startTime":1238.01,"endTime":1241.22,"body":"a very low heat capacity,"},{"startTime":1241.22,"endTime":1242.3,"body":"compared to the ocean."},{"startTime":1242.3,"endTime":1243.8,"body":"It's much easier to warm,"},{"startTime":1243.8,"endTime":1245.54,"body":"it doesn't take nearly as much energy,"},{"startTime":1245.54,"endTime":1248.552,"body":"to warm air up as it"},{"startTime":1245.54,"endTime":1248.552,"body":"takes to warm water up."},{"startTime":1248.552,"endTime":1250.67,"body":"And the land one is quite small,"},{"startTime":1250.67,"endTime":1254.78,"body":"because the land only"},{"startTime":1250.67,"endTime":1254.78,"body":"the soil really warms up,"},{"startTime":1254.78,"endTime":1256.691,"body":"the sort of top few, you're not,"},{"startTime":1256.691,"endTime":1260.933,"body":"whereas in the oceans you're"},{"startTime":1256.691,"endTime":1260.933,"body":"warming up kilometers of water."},{"startTime":1262.37,"endTime":1265.46,"body":"So why is the energy being"},{"startTime":1262.37,"endTime":1265.46,"body":"distributed the way it is,"},{"startTime":1265.46,"endTime":1266.84,"body":"just to point at you?"},{"startTime":1266.84,"endTime":1270.614,"body":"Most of it is in the top 700 meters,"},{"startTime":1270.614,"endTime":1275.614,"body":"more than half is confined to"},{"startTime":1270.614,"endTime":1275.614,"body":"that top 700 meters of water."},{"startTime":1275.739,"endTime":1280.739,"body":"A lot of it's in the top"},{"startTime":1275.739,"endTime":1280.739,"body":"300 meters and the rest,"},{"startTime":1280.76,"endTime":1283.82,"body":"most of the rest is going"},{"startTime":1280.76,"endTime":1283.82,"body":"down into the ocean depths."},{"startTime":1283.82,"endTime":1284.72,"body":"So why is this?"},{"startTime":1284.72,"endTime":1286.67,"body":"You can sort of see what's happening here."},{"startTime":1286.67,"endTime":1289.91,"body":"These are temperature"},{"startTime":1286.67,"endTime":1289.91,"body":"trends in the global oceans."},{"startTime":1289.91,"endTime":1292.55,"body":"And you can see here in"},{"startTime":1289.91,"endTime":1292.55,"body":"the Pacific in particular,"},{"startTime":1292.55,"endTime":1294.5,"body":"all the warmings happening at the surface,"},{"startTime":1294.5,"endTime":1296.926,"body":"really nothing happening further down."},{"startTime":1296.926,"endTime":1300.17,"body":"In the Atlantic it is penetrating down,"},{"startTime":1300.17,"endTime":1304.13,"body":"but only in a few regions"},{"startTime":1300.17,"endTime":1304.13,"body":"that region of North Atlantic,"},{"startTime":1304.13,"endTime":1306.41,"body":"that region of the southern ocean, okay?"},{"startTime":1306.41,"endTime":1308.54,"body":"Those same regions that we've said,"},{"startTime":1308.54,"endTime":1312.47,"body":"we've seen water penetrating"},{"startTime":1308.54,"endTime":1312.47,"body":"down into the ocean depths,"},{"startTime":1312.47,"endTime":1314.18,"body":"because those are the regions where,"},{"startTime":1314.18,"endTime":1317.24,"body":"the surface is connected to the deep ocean"},{"startTime":1317.24,"endTime":1320.18,"body":"and we get this siphoning"},{"startTime":1317.24,"endTime":1320.18,"body":"off of surface waters."},{"startTime":1320.18,"endTime":1322.1,"body":"And as the surface warms,"},{"startTime":1322.1,"endTime":1324.263,"body":"you get a siphoning off of surface heat."},{"startTime":1325.13,"endTime":1328.88,"body":"So that's where the"},{"startTime":1325.13,"endTime":1328.88,"body":"energy penetrates down,"},{"startTime":1328.88,"endTime":1331.283,"body":"into the ocean depths."},{"startTime":1332.68,"endTime":1336.62,"body":"So this is what takes us"},{"startTime":1332.68,"endTime":1336.62,"body":"back to our climate model,"},{"startTime":1336.62,"endTime":1341.453,"body":"our Gresham climate model,"},{"startTime":1336.62,"endTime":1341.453,"body":"which I will wake up I hope."},{"startTime":1342.35,"endTime":1344.303,"body":"And just to remind you,"},{"startTime":1346.04,"endTime":1348.71,"body":"this so fluid flowing in,"},{"startTime":1348.71,"endTime":1352.39,"body":"represents energy coming in from the sun."},{"startTime":1352.39,"endTime":1354.53,"body":"I explained in the last lecture,"},{"startTime":1354.53,"endTime":1357.08,"body":"that if I was to make this to scale,"},{"startTime":1357.08,"endTime":1359.6,"body":"because the energy flowing in"},{"startTime":1357.08,"endTime":1359.6,"body":"from the sun is so enormous,"},{"startTime":1359.6,"endTime":1362.39,"body":"compared to the changes"},{"startTime":1359.6,"endTime":1362.39,"body":"due to greenhouse gases,"},{"startTime":1362.39,"endTime":1364.52,"body":"we'd need to have it sort"},{"startTime":1362.39,"endTime":1364.52,"body":"of a hundred meters high"},{"startTime":1364.52,"endTime":1366.61,"body":"and Gresham couldn't quite afford that."},{"startTime":1366.61,"endTime":1371.61,"body":"So this is scale down the natural flow,"},{"startTime":1371.78,"endTime":1373.52,"body":"flowing in from the sun"},{"startTime":1373.52,"endTime":1377.18,"body":"and flowing back out into space, okay?"},{"startTime":1377.18,"endTime":1379.31,"body":"Space is downwards, okay?"},{"startTime":1379.31,"endTime":1380.6,"body":"Again Gresham couldn't afford,"},{"startTime":1380.6,"endTime":1384.23,"body":"a sort of anti-gravity arrangement but so,"},{"startTime":1384.23,"endTime":1386.09,"body":"but you can see the basic idea,"},{"startTime":1386.09,"endTime":1388.73,"body":"that we have a balance in"},{"startTime":1386.09,"endTime":1388.73,"body":"energy flowing in from the sun"},{"startTime":1388.73,"endTime":1391.1,"body":"and energy flowing back out into space."},{"startTime":1391.1,"endTime":1396.1,"body":"If we crank it up to, if we"},{"startTime":1391.1,"endTime":1396.1,"body":"increase the speed of the pump,"},{"startTime":1398.99,"endTime":1403.99,"body":"we see the level of"},{"startTime":1398.99,"endTime":1403.99,"body":"water in this tube rises,"},{"startTime":1406.34,"endTime":1411.34,"body":"pushing fluid out into space"},{"startTime":1406.34,"endTime":1411.34,"body":"energy back out into space,"},{"startTime":1412.16,"endTime":1415.4,"body":"that corresponds to temperature"},{"startTime":1412.16,"endTime":1415.4,"body":"the surface temperature"},{"startTime":1415.4,"endTime":1419.45,"body":"and it rapidly reaches"},{"startTime":1415.4,"endTime":1419.45,"body":"a new equilibrium level."},{"startTime":1419.45,"endTime":1424.45,"body":"And if I increase the speed"},{"startTime":1419.45,"endTime":1424.45,"body":"by the same amount again,"},{"startTime":1427.79,"endTime":1432.35,"body":"it goes up by about the same"},{"startTime":1427.79,"endTime":1432.35,"body":"amount again, all right?"},{"startTime":1432.35,"endTime":1436.7,"body":"So far, so good, so far so simple"},{"startTime":1436.7,"endTime":1440.54,"body":"and relatively obvious this would be,"},{"startTime":1440.54,"endTime":1443.48,"body":"the way the climate would behave,"},{"startTime":1443.48,"endTime":1447.48,"body":"if the whole world were"},{"startTime":1443.48,"endTime":1447.48,"body":"kind of like the Pacific"},{"startTime":1448.52,"endTime":1452.54,"body":"and you just had a sort"},{"startTime":1448.52,"endTime":1452.54,"body":"of surface of water,"},{"startTime":1452.54,"endTime":1455.003,"body":"completely isolated from"},{"startTime":1452.54,"endTime":1455.003,"body":"the water underneath."},{"startTime":1456.633,"endTime":1458.19,"body":"But it isn't"},{"startTime":1459.29,"endTime":1461.875,"body":"and this is why we need to think about,"},{"startTime":1461.875,"endTime":1463.7,"body":"the way the oceans behave,"},{"startTime":1463.7,"endTime":1465.05,"body":"the way the deep oceans behave,"},{"startTime":1465.05,"endTime":1469.28,"body":"in order to understand"},{"startTime":1465.05,"endTime":1469.28,"body":"how the climate responds."},{"startTime":1469.28,"endTime":1471.08,"body":"So as I promised in the last lecture,"},{"startTime":1471.08,"endTime":1473.24,"body":"this is the bit where we uncork the ocean."},{"startTime":1473.24,"endTime":1476.407,"body":"I'll switch this off before I do that."},{"startTime":1476.407,"endTime":1479.074,"body":"(machine whirs)"},{"startTime":1481.85,"endTime":1486.85,"body":"And now I'm going to drain this quickly."},{"startTime":1489.95,"endTime":1493.04,"body":"Sadly there isn't a tap at the"},{"startTime":1489.95,"endTime":1493.04,"body":"bottom of the global ocean,"},{"startTime":1493.04,"endTime":1495.233,"body":"to cool it down again if only,"},{"startTime":1496.25,"endTime":1501.25,"body":"but so what this pipe"},{"startTime":1496.25,"endTime":1501.25,"body":"represents is the heat content,"},{"startTime":1505.49,"endTime":1508.1,"body":"the sort of fluid in this pipe,"},{"startTime":1508.1,"endTime":1511.53,"body":"is the heat content of the deep oceans"},{"startTime":1512.726,"endTime":1516.113,"body":"and therefore that level"},{"startTime":1512.726,"endTime":1516.113,"body":"of water in the pipe,"},{"startTime":1517.25,"endTime":1519.89,"body":"is proportional to the sort of,"},{"startTime":1519.89,"endTime":1523.613,"body":"average deep ocean temperature, okay?"},{"startTime":1524.45,"endTime":1527.518,"body":"And this pipe is fatter than this one,"},{"startTime":1527.518,"endTime":1530.72,"body":"because the oceans have"},{"startTime":1527.518,"endTime":1530.72,"body":"a bigger heat capacity,"},{"startTime":1530.72,"endTime":1532.19,"body":"than the atmosphere."},{"startTime":1532.19,"endTime":1534.92,"body":"So it takes more fluid,"},{"startTime":1534.92,"endTime":1538.203,"body":"more energy to push up the"},{"startTime":1534.92,"endTime":1538.203,"body":"temperatures of the oceans,"},{"startTime":1538.203,"endTime":1540.92,"body":"than it takes to push up the temperature,"},{"startTime":1540.92,"endTime":1543.433,"body":"than it takes to push up the"},{"startTime":1540.92,"endTime":1543.433,"body":"temperature of the atmosphere."},{"startTime":1544.67,"endTime":1547.22,"body":"Just to start with, to"},{"startTime":1544.67,"endTime":1547.22,"body":"make things really simple,"},{"startTime":1547.22,"endTime":1549.503,"body":"let's imagine the ocean,"},{"startTime":1550.37,"endTime":1555.37,"body":"that this pipe is"},{"startTime":1550.37,"endTime":1555.37,"body":"absolutely enormous, okay?"},{"startTime":1555.5,"endTime":1557.48,"body":"So just to sort of imagine first,"},{"startTime":1557.48,"endTime":1561.38,"body":"the oceans are infinitely big, okay?"},{"startTime":1561.38,"endTime":1564.77,"body":"So I just opened this tap,"},{"startTime":1561.38,"endTime":1564.77,"body":"it's sort of tricking out here."},{"startTime":1564.77,"endTime":1568.37,"body":"So now the level in there can't change,"},{"startTime":1568.37,"endTime":1570.523,"body":"'cause I've just opened"},{"startTime":1568.37,"endTime":1570.523,"body":"the tap at the bottom."},{"startTime":1571.91,"endTime":1573.77,"body":"If I now do what I did before,"},{"startTime":1573.77,"endTime":1577.663,"body":"so I'll switch it back on again, okay?"},{"startTime":1581.21,"endTime":1584.323,"body":"And wait till it's back"},{"startTime":1581.21,"endTime":1584.323,"body":"in equilibrium, okay?"},{"startTime":1586.97,"endTime":1590.93,"body":"So it's now back in equilibrium, okay?"},{"startTime":1590.93,"endTime":1595.93,"body":"Now I'm going to increase my"},{"startTime":1590.93,"endTime":1595.93,"body":"greenhouse gas concentrations,"},{"startTime":1598.46,"endTime":1599.48,"body":"in the atmosphere,"},{"startTime":1599.48,"endTime":1602.355,"body":"increase the rate of turning of the pump,"},{"startTime":1602.355,"endTime":1607.355,"body":"by the same amount that I did"},{"startTime":1602.355,"endTime":1607.355,"body":"the first time before, okay?"},{"startTime":1607.392,"endTime":1612.392,"body":"By the same speed increase of the pump."},{"startTime":1614.48,"endTime":1616.13,"body":"Does anybody want to suggest,"},{"startTime":1616.13,"endTime":1619.87,"body":"what is now going to happen"},{"startTime":1616.13,"endTime":1619.87,"body":"this time to the level of water,"},{"startTime":1619.87,"endTime":1623.57,"body":"to the level of fluid"},{"startTime":1619.87,"endTime":1623.57,"body":"in the atmosphere pipe,"},{"startTime":1623.57,"endTime":1625.01,"body":"compared to what happened the last time?"},{"startTime":1625.01,"endTime":1626.6,"body":"Remember the last time"},{"startTime":1625.01,"endTime":1626.6,"body":"it went up to about here,"},{"startTime":1626.6,"endTime":1628.51,"body":"the first time I did it."},{"startTime":1628.51,"endTime":1630.71,"body":"What do you think is"},{"startTime":1628.51,"endTime":1630.71,"body":"going to happen this time?"},{"startTime":1633.26,"endTime":1635.45,"body":"Does it, water is"},{"startTime":1633.26,"endTime":1635.45,"body":"flowing out through here,"},{"startTime":1635.45,"endTime":1638.78,"body":"into the ocean and through"},{"startTime":1635.45,"endTime":1638.78,"body":"here, back out into space."},{"startTime":1638.78,"endTime":1639.92,"body":"So there's two out outlets now,"},{"startTime":1639.92,"endTime":1641.37,"body":"whereas before there was one."},{"startTime":1642.212,"endTime":1646.37,"body":"So just to sort of get your thinking,"},{"startTime":1646.37,"endTime":1648.38,"body":"what do you think's going to happen?"},{"startTime":1648.38,"endTime":1651.47,"body":"So before when I increase the pump speed,"},{"startTime":1651.47,"endTime":1653.695,"body":"it came up to about here,"},{"startTime":1653.695,"endTime":1655.845,"body":"what do you think's going"},{"startTime":1653.695,"endTime":1655.845,"body":"to happen this time?"},{"startTime":1656.959,"endTime":1659.06,"body":"Yeah, it'll come up a bit lower."},{"startTime":1659.06,"endTime":1660.761,"body":"Let's do the experiment."},{"startTime":1660.761,"endTime":1663.35,"body":"(machine whirs)"},{"startTime":1663.35,"endTime":1664.183,"body":"Okay?"},{"startTime":1665.869,"endTime":1670.04,"body":"And it's warmed up but not as much, okay?"},{"startTime":1670.04,"endTime":1675.04,"body":"About half what it would do"},{"startTime":1670.04,"endTime":1675.04,"body":"if it actually was allowed to,"},{"startTime":1675.2,"endTime":1678.59,"body":"if it was actually just"},{"startTime":1675.2,"endTime":1678.59,"body":"the tropical Pacific,"},{"startTime":1678.59,"endTime":1682.253,"body":"just isolated from the oceans."},{"startTime":1683.468,"endTime":1687.533,"body":"And if I do it again, I can see that,"},{"startTime":1688.684,"endTime":1692.21,"body":"again if I increase it"},{"startTime":1688.684,"endTime":1692.21,"body":"to that faster rate,"},{"startTime":1692.21,"endTime":1695.183,"body":"that I had before again it goes up again."},{"startTime":1696.08,"endTime":1698.453,"body":"But again, by about"},{"startTime":1696.08,"endTime":1698.453,"body":"half what it did before."},{"startTime":1699.62,"endTime":1703.644,"body":"So in the early stages of global warming,"},{"startTime":1703.644,"endTime":1706.4,"body":"where energy's being"},{"startTime":1703.644,"endTime":1706.4,"body":"carried off into the ocean,"},{"startTime":1706.4,"endTime":1709.73,"body":"as well as energy going"},{"startTime":1706.4,"endTime":1709.73,"body":"back out into space,"},{"startTime":1709.73,"endTime":1714.73,"body":"you see much less of the"},{"startTime":1709.73,"endTime":1714.73,"body":"warming you eventually see,"},{"startTime":1714.95,"endTime":1717.263,"body":"when the system comes"},{"startTime":1714.95,"endTime":1717.263,"body":"back into equilibrium."},{"startTime":1718.37,"endTime":1722.6,"body":"And this is really important"},{"startTime":1718.37,"endTime":1722.6,"body":"because it means that,"},{"startTime":1722.6,"endTime":1727.07,"body":"if we were to keep our"},{"startTime":1722.6,"endTime":1727.07,"body":"concentrations of greenhouse gases,"},{"startTime":1727.07,"endTime":1730.103,"body":"in the atmosphere constant"},{"startTime":1727.07,"endTime":1730.103,"body":"at today's level forever,"},{"startTime":1731.114,"endTime":1735.35,"body":"we wouldn't just see the"},{"startTime":1731.114,"endTime":1735.35,"body":"warming we've already seen,"},{"startTime":1735.35,"endTime":1737.21,"body":"it would keep warming."},{"startTime":1737.21,"endTime":1738.14,"body":"And this is why it's really important,"},{"startTime":1738.14,"endTime":1739.7,"body":"to understand this process,"},{"startTime":1739.7,"endTime":1743.12,"body":"which is what we're focusing"},{"startTime":1739.7,"endTime":1743.12,"body":"on in these lectures."},{"startTime":1743.12,"endTime":1748.12,"body":"So there's in equations, that's"},{"startTime":1743.12,"endTime":1748.12,"body":"the earth's climate system,"},{"startTime":1749.39,"endTime":1751.521,"body":"exactly the same principle."},{"startTime":1751.521,"endTime":1753.83,"body":"That's the extra energy flowing in,"},{"startTime":1753.83,"endTime":1755.78,"body":"due to the increasing greenhouse gases."},{"startTime":1755.78,"endTime":1757.55,"body":"And then there's this important parameter,"},{"startTime":1757.55,"endTime":1758.51,"body":"which is the efficiency,"},{"startTime":1758.51,"endTime":1761.51,"body":"we literally earth gets"},{"startTime":1758.51,"endTime":1761.51,"body":"rid of energy to space,"},{"startTime":1761.51,"endTime":1763.91,"body":"that's the plastic tube"},{"startTime":1761.51,"endTime":1763.91,"body":"with an open outlet pipe,"},{"startTime":1763.91,"endTime":1765.56,"body":"that was the first one we had."},{"startTime":1765.56,"endTime":1767.0,"body":"And here's the new one,"},{"startTime":1767.0,"endTime":1769.55,"body":"where we've got two outlet pipes, okay?"},{"startTime":1769.55,"endTime":1772.04,"body":"And you'll see that because"},{"startTime":1769.55,"endTime":1772.04,"body":"there's two of these Ks,"},{"startTime":1772.04,"endTime":1776.42,"body":"you need less H for the same F, okay?"},{"startTime":1776.42,"endTime":1778.752,"body":"Because this is a bigger number now."},{"startTime":1778.752,"endTime":1781.22,"body":"And we can sort of do"},{"startTime":1778.752,"endTime":1781.22,"body":"exactly the same thing,"},{"startTime":1781.22,"endTime":1782.54,"body":"with the climate system,"},{"startTime":1782.54,"endTime":1785.03,"body":"because we've got this extra term,"},{"startTime":1785.03,"endTime":1787.64,"body":"energy being transported"},{"startTime":1785.03,"endTime":1787.64,"body":"down into the ocean."},{"startTime":1787.64,"endTime":1791.12,"body":"We see less heating for the"},{"startTime":1787.64,"endTime":1791.12,"body":"same amount of increase,"},{"startTime":1791.12,"endTime":1792.983,"body":"in greenhouse gas concentrations."},{"startTime":1794.93,"endTime":1797.6,"body":"It's also really important to use this."},{"startTime":1797.6,"endTime":1799.04,"body":"You can understand it's a model,"},{"startTime":1799.04,"endTime":1803.51,"body":"not just of the total amount"},{"startTime":1799.04,"endTime":1803.51,"body":"of increase in height,"},{"startTime":1803.51,"endTime":1806.96,"body":"in depth of the ocean,"},{"startTime":1806.96,"endTime":1811.7,"body":"but it's a good model of"},{"startTime":1806.96,"endTime":1811.7,"body":"how it responds to changes,"},{"startTime":1811.7,"endTime":1814.4,"body":"in the incoming flow."},{"startTime":1814.4,"endTime":1817.183,"body":"So if I change the"},{"startTime":1814.4,"endTime":1817.183,"body":"incoming flow down again,"},{"startTime":1817.183,"endTime":1819.85,"body":"(machine whirs)"},{"startTime":1821.125,"endTime":1825.563,"body":"that means delta F the"},{"startTime":1821.125,"endTime":1825.563,"body":"change in F was negative."},{"startTime":1826.4,"endTime":1829.647,"body":"So my delta H is negative."},{"startTime":1829.647,"endTime":1834.11,"body":"It falls and it falls quickly, okay?"},{"startTime":1834.11,"endTime":1834.943,"body":"I bump it up again."},{"startTime":1834.943,"endTime":1839.63,"body":"So it's a good model of"},{"startTime":1834.943,"endTime":1839.63,"body":"how a change in flow,"},{"startTime":1839.63,"endTime":1841.673,"body":"affects a change in heights."},{"startTime":1843.28,"endTime":1846.891,"body":"So we can go further than this."},{"startTime":1846.891,"endTime":1848.45,"body":"Same goes for temperature."},{"startTime":1848.45,"endTime":1851.36,"body":"It's a great model of how a"},{"startTime":1848.45,"endTime":1851.36,"body":"change in greenhouse gases,"},{"startTime":1851.36,"endTime":1855.113,"body":"on short time scales causes"},{"startTime":1851.36,"endTime":1855.113,"body":"a change in temperature."},{"startTime":1856.724,"endTime":1859.22,"body":"But now we've got to do something,"},{"startTime":1859.22,"endTime":1860.63,"body":"make it a little bit more interesting,"},{"startTime":1860.63,"endTime":1864.083,"body":"because the oceans are not infinite."},{"startTime":1867.23,"endTime":1870.38,"body":"We know that the energy's"},{"startTime":1867.23,"endTime":1870.38,"body":"got to go somewhere,"},{"startTime":1870.38,"endTime":1872.69,"body":"it's going down into the deep oceans"},{"startTime":1872.69,"endTime":1877.313,"body":"and causing them to warm up."},{"startTime":1878.51,"endTime":1881.566,"body":"And that's represented by the increase,"},{"startTime":1881.566,"endTime":1885.26,"body":"in the level of the fluid over here."},{"startTime":1885.26,"endTime":1886.34,"body":"But let's start off here."},{"startTime":1886.34,"endTime":1891.34,"body":"Now we are just taking this"},{"startTime":1886.34,"endTime":1891.34,"body":"back down to its sort of quotes,"},{"startTime":1891.65,"endTime":1894.38,"body":"pre-industrial level, okay?"},{"startTime":1894.38,"endTime":1897.77,"body":"So here we are, it's back"},{"startTime":1894.38,"endTime":1897.77,"body":"in equilibrium, okay?"},{"startTime":1897.77,"endTime":1900.95,"body":"It's down at the really"},{"startTime":1897.77,"endTime":1900.95,"body":"this is the natural flow,"},{"startTime":1900.95,"endTime":1903.223,"body":"of energy into the climate system."},{"startTime":1903.223,"endTime":1908.223,"body":"And now do you see the fluid"},{"startTime":1903.223,"endTime":1908.223,"body":"is flowing back out into space?"},{"startTime":1910.67,"endTime":1915.67,"body":"It can flow between these"},{"startTime":1910.67,"endTime":1915.67,"body":"two pipes, but right now,"},{"startTime":1915.74,"endTime":1918.503,"body":"because the level's about"},{"startTime":1915.74,"endTime":1918.503,"body":"the same between them,"},{"startTime":1920.18,"endTime":1921.92,"body":"it's not flowing, yep?"},{"startTime":1921.92,"endTime":1923.783,"body":"Because it's balancing on both sides."},{"startTime":1925.58,"endTime":1927.2,"body":"So now this is the hard part."},{"startTime":1927.2,"endTime":1928.943,"body":"What's going to happen now,"},{"startTime":1929.9,"endTime":1932.614,"body":"if I crank up the speed of the pump?"},{"startTime":1932.614,"endTime":1935.281,"body":"(machine whirs)"},{"startTime":1938.06,"endTime":1939.213,"body":"Someone go for it."},{"startTime":1944.037,"endTime":1945.577,"body":"- [Female Speaker] Does it rise up?"},{"startTime":1945.577,"endTime":1949.22,"body":"- It rises initially"},{"startTime":1945.577,"endTime":1949.22,"body":"and it rises initially,"},{"startTime":1949.22,"endTime":1951.17,"body":"just as much as it did before."},{"startTime":1951.17,"endTime":1956.17,"body":"And then so with the infinite ocean, yep?"},{"startTime":1957.02,"endTime":1959.36,"body":"So it'll rise, I will do it in a minute,"},{"startTime":1959.36,"endTime":1961.88,"body":"but I want you to think"},{"startTime":1959.36,"endTime":1961.88,"body":"about it before we do it."},{"startTime":1961.88,"endTime":1963.061,"body":"'Cause afterwards,"},{"startTime":1963.061,"endTime":1964.37,"body":"one of the things in science is,"},{"startTime":1964.37,"endTime":1967.01,"body":"everything's always leading"},{"startTime":1964.37,"endTime":1967.01,"body":"obvious when you've done it."},{"startTime":1967.01,"endTime":1969.83,"body":"Yeah, you never find a"},{"startTime":1967.01,"endTime":1969.83,"body":"scientist who'll admit,"},{"startTime":1969.83,"endTime":1972.159,"body":"that they never didn't"},{"startTime":1969.83,"endTime":1972.159,"body":"understand something,"},{"startTime":1972.159,"endTime":1974.03,"body":"at some point in the past,"},{"startTime":1974.03,"endTime":1975.74,"body":"because it's always like, oh yeah, yeah,"},{"startTime":1975.74,"endTime":1977.09,"body":"it's always like net zero,"},{"startTime":1977.09,"endTime":1978.77,"body":"everything's net zero is totally obvious."},{"startTime":1978.77,"endTime":1982.13,"body":"In fact, 15 years ago it wasn't obvious."},{"startTime":1982.13,"endTime":1983.66,"body":"I have to keep reminding myself this."},{"startTime":1983.66,"endTime":1988.66,"body":"Anyway, so do think about what'll happen."},{"startTime":1988.706,"endTime":1990.732,"body":"It'll jump up to here,"},{"startTime":1990.732,"endTime":1995.732,"body":"but then what's going to happen"},{"startTime":1990.732,"endTime":1995.732,"body":"to the fluid in this pipe?"},{"startTime":1996.95,"endTime":1999.47,"body":"It's going to start rising."},{"startTime":1999.47,"endTime":2002.233,"body":"It's going to rise slower"},{"startTime":1999.47,"endTime":2002.233,"body":"because it's a fatter pipe."},{"startTime":2003.31,"endTime":2006.633,"body":"And what's then going to happen"},{"startTime":2003.31,"endTime":2006.633,"body":"to the fluid in this pipe?"},{"startTime":2006.633,"endTime":2009.3,"body":"(machine whirs)"},{"startTime":2011.59,"endTime":2013.653,"body":"Should we just do it and see what happens?"},{"startTime":2014.53,"endTime":2018.433,"body":"Okay, I'll go for the"},{"startTime":2014.53,"endTime":2018.433,"body":"slightly bigger acceleration."},{"startTime":2020.11,"endTime":2022.12,"body":"So you can see it immediately pushes up."},{"startTime":2022.12,"endTime":2025.93,"body":"This is the faster speed"},{"startTime":2022.12,"endTime":2025.93,"body":"immediately it goes up"},{"startTime":2025.93,"endTime":2027.763,"body":"and then it seems to stop rising."},{"startTime":2029.89,"endTime":2030.82,"body":"But what's happening now,"},{"startTime":2030.82,"endTime":2033.37,"body":"watch it carefully compared"},{"startTime":2030.82,"endTime":2033.37,"body":"to the ticks behind it."},{"startTime":2035.267,"endTime":2036.4,"body":"(machine whirs)"},{"startTime":2036.4,"endTime":2038.56,"body":"So this is constant concentrations,"},{"startTime":2038.56,"endTime":2040.24,"body":"of greenhouse gases in the atmosphere."},{"startTime":2040.24,"endTime":2042.16,"body":"Remember the wording"},{"startTime":2040.24,"endTime":2042.16,"body":"of the Rio Convention."},{"startTime":2042.16,"endTime":2044.47,"body":"We're going to stabilize"},{"startTime":2042.16,"endTime":2044.47,"body":"atmospheric concentrations,"},{"startTime":2044.47,"endTime":2046.51,"body":"of greenhouse gases at a level,"},{"startTime":2046.51,"endTime":2048.46,"body":"that will prevent dangerous"},{"startTime":2046.51,"endTime":2048.46,"body":"anthropogenic interference,"},{"startTime":2048.46,"endTime":2049.57,"body":"in the climate system."},{"startTime":2049.57,"endTime":2052.93,"body":"Those are the words of the"},{"startTime":2049.57,"endTime":2052.93,"body":"Rio Convention in 1992."},{"startTime":2052.93,"endTime":2056.11,"body":"So the level of greenhouse"},{"startTime":2052.93,"endTime":2056.11,"body":"gases in the atmosphere,"},{"startTime":2056.11,"endTime":2057.22,"body":"is constant."},{"startTime":2057.22,"endTime":2059.29,"body":"The pump is set at a constant rate."},{"startTime":2059.29,"endTime":2062.62,"body":"What's happening to this"},{"startTime":2059.29,"endTime":2062.62,"body":"surface temperature?"},{"startTime":2062.62,"endTime":2065.547,"body":"Somebody's close, it's still rising, yeah?"},{"startTime":2070.24,"endTime":2075.24,"body":"It's rising very slowly and"},{"startTime":2070.24,"endTime":2075.24,"body":"it's very hard to predict,"},{"startTime":2075.82,"endTime":2077.863,"body":"when that rise is going to stop,"},{"startTime":2079.6,"endTime":2082.69,"body":"because in order to know that,"},{"startTime":2082.69,"endTime":2084.177,"body":"you need to know"},{"startTime":2082.69,"endTime":2084.177,"body":"everything that's going on,"},{"startTime":2084.177,"endTime":2085.45,"body":"in the deep oceans."},{"startTime":2085.45,"endTime":2086.47,"body":"And as I emphasized,"},{"startTime":2086.47,"endTime":2087.67,"body":"it's quite hard to see everything,"},{"startTime":2087.67,"endTime":2090.16,"body":"that's going on in the deep oceans."},{"startTime":2090.16,"endTime":2095.16,"body":"So let's take this back down to zero again"},{"startTime":2095.92,"endTime":2100.09,"body":"and cool off our deep ocean."},{"startTime":2100.09,"endTime":2102.033,"body":"So we can do some more"},{"startTime":2100.09,"endTime":2102.033,"body":"experiments with it."},{"startTime":2103.03,"endTime":2108.03,"body":"Here we are back down to where we started."},{"startTime":2112.882,"endTime":2114.882,"body":"So that's our all right?"},{"startTime":2123.962,"endTime":2128.962,"body":"So that's our new system."},{"startTime":2129.756,"endTime":2132.58,"body":"Now with the ocean in,"},{"startTime":2132.58,"endTime":2134.95,"body":"let's think about in a"},{"startTime":2132.58,"endTime":2134.95,"body":"little bit more detail,"},{"startTime":2134.95,"endTime":2137.11,"body":"of what actually happens,"},{"startTime":2137.11,"endTime":2140.08,"body":"when we crank up the speed of the pump."},{"startTime":2140.08,"endTime":2144.403,"body":"So I'll switch it up to by a factor of,"},{"startTime":2146.05,"endTime":2149.691,"body":"I'll increase the pump"},{"startTime":2146.05,"endTime":2149.691,"body":"speed by sort of one unit."},{"startTime":2149.691,"endTime":2151.483,"body":"That was the first time we did."},{"startTime":2152.53,"endTime":2153.603,"body":"And this is what happens."},{"startTime":2153.603,"endTime":2156.56,"body":"You see this goes up by that much"},{"startTime":2158.8,"endTime":2161.983,"body":"and then this is going"},{"startTime":2158.8,"endTime":2161.983,"body":"up at a certain speed."},{"startTime":2162.91,"endTime":2163.743,"body":"And so this is,"},{"startTime":2163.743,"endTime":2167.413,"body":"it's pushing this up at a"},{"startTime":2163.743,"endTime":2167.413,"body":"certain slow speed as well."},{"startTime":2168.52,"endTime":2170.353,"body":"If I do it again,"},{"startTime":2174.55,"endTime":2178.39,"body":"it goes jumps up by the same amount again."},{"startTime":2178.39,"endTime":2182.2,"body":"And the speed with which this is going up,"},{"startTime":2182.2,"endTime":2184.723,"body":"also goes up by the same amount again."},{"startTime":2187.36,"endTime":2190.153,"body":"Now you'll probably be relieved to hear,"},{"startTime":2192.04,"endTime":2193.54,"body":"we're going to go back to some maths."},{"startTime":2193.54,"endTime":2197.05,"body":"The whole point of this is"},{"startTime":2193.54,"endTime":2197.05,"body":"to make you feel relieved,"},{"startTime":2197.05,"endTime":2198.253,"body":"to see some more maths."},{"startTime":2199.433,"endTime":2200.83,"body":"Here we are."},{"startTime":2200.83,"endTime":2205.83,"body":"So the change in depth that"},{"startTime":2200.83,"endTime":2205.83,"body":"we see in a short time,"},{"startTime":2209.23,"endTime":2210.25,"body":"in a short time interval,"},{"startTime":2210.25,"endTime":2214.72,"body":"a few seconds in that system"},{"startTime":2210.25,"endTime":2214.72,"body":"is proportional to two things."},{"startTime":2214.72,"endTime":2217.09,"body":"One thing that we know all about,"},{"startTime":2217.09,"endTime":2219.659,"body":"which is the change in fluid flow,"},{"startTime":2219.659,"endTime":2223.253,"body":"that would be the same even"},{"startTime":2219.659,"endTime":2223.253,"body":"if the deep ocean wasn't there"},{"startTime":2223.253,"endTime":2227.61,"body":"or even if the deep ocean"},{"startTime":2223.253,"endTime":2227.61,"body":"was infinitely large, okay?"},{"startTime":2227.61,"endTime":2229.033,"body":"So that's that first term."},{"startTime":2229.967,"endTime":2234.91,"body":"But there's another term"},{"startTime":2229.967,"endTime":2234.91,"body":"which is a rate of increase,"},{"startTime":2234.91,"endTime":2238.54,"body":"that depends on how fast"},{"startTime":2234.91,"endTime":2238.54,"body":"the pump is turning."},{"startTime":2238.54,"endTime":2241.69,"body":"The pump's turning"},{"startTime":2238.54,"endTime":2241.69,"body":"quickly, it rises quickly."},{"startTime":2241.69,"endTime":2244.27,"body":"If the pump's turning slowly,"},{"startTime":2244.27,"endTime":2248.053,"body":"it doesn't, it rises at a slower rate."},{"startTime":2248.92,"endTime":2250.36,"body":"So you've got one term,"},{"startTime":2250.36,"endTime":2255.22,"body":"which depends on the"},{"startTime":2250.36,"endTime":2255.22,"body":"change in fluid input flow,"},{"startTime":2255.22,"endTime":2256.66,"body":"over that time interval."},{"startTime":2256.66,"endTime":2260.08,"body":"And another term that depends"},{"startTime":2256.66,"endTime":2260.08,"body":"on the average fluid flow,"},{"startTime":2260.08,"endTime":2261.28,"body":"over that time interval."},{"startTime":2262.211,"endTime":2264.703,"body":"And now what's really interesting is,"},{"startTime":2266.036,"endTime":2267.7,"body":"you can reorganize this,"},{"startTime":2267.7,"endTime":2269.83,"body":"by the way this is"},{"startTime":2267.7,"endTime":2269.83,"body":"exactly the same equation,"},{"startTime":2269.83,"endTime":2273.46,"body":"just I've replaced this,"},{"startTime":2269.83,"endTime":2273.46,"body":"there's two constants here,"},{"startTime":2273.46,"endTime":2275.92,"body":"but I can replace them with one constant,"},{"startTime":2275.92,"endTime":2280.69,"body":"that represents the sort of"},{"startTime":2275.92,"endTime":2280.69,"body":"responsiveness to the flow."},{"startTime":2280.69,"endTime":2282.64,"body":"That's this kappa thing here."},{"startTime":2282.64,"endTime":2284.86,"body":"And then this other one which represents,"},{"startTime":2284.86,"endTime":2288.85,"body":"the rate at which it"},{"startTime":2284.86,"endTime":2288.85,"body":"adjusts to a constant flow."},{"startTime":2288.85,"endTime":2292.63,"body":"That was the gradual rate at"},{"startTime":2288.85,"endTime":2292.63,"body":"which it carried on adjusting,"},{"startTime":2292.63,"endTime":2294.433,"body":"after I made the flow constant."},{"startTime":2296.68,"endTime":2298.54,"body":"And this is where it gets interesting."},{"startTime":2298.54,"endTime":2303.313,"body":"We can do exactly the same thing"},{"startTime":2298.54,"endTime":2303.313,"body":"for the global temperature."},{"startTime":2304.3,"endTime":2306.79,"body":"The change in global temperature,"},{"startTime":2306.79,"endTime":2309.76,"body":"over a multi-decade time interval,"},{"startTime":2309.76,"endTime":2312.94,"body":"is proportional to one term,"},{"startTime":2312.94,"endTime":2315.85,"body":"which is just the change in"},{"startTime":2312.94,"endTime":2315.85,"body":"greenhouse gas concentrations,"},{"startTime":2315.85,"endTime":2317.053,"body":"over that time interval."},{"startTime":2318.13,"endTime":2320.92,"body":"And another term that's the average,"},{"startTime":2320.92,"endTime":2323.44,"body":"greenhouse gas concentrations"},{"startTime":2320.92,"endTime":2323.44,"body":"over that time interval,"},{"startTime":2323.44,"endTime":2325.74,"body":"multiplied by the length"},{"startTime":2323.44,"endTime":2325.74,"body":"of the time interval."},{"startTime":2327.28,"endTime":2331.123,"body":"So you think, well, okay, that"},{"startTime":2327.28,"endTime":2331.123,"body":"seemed like a lot of work."},{"startTime":2332.02,"endTime":2334.3,"body":"Where does this get us?"},{"startTime":2334.3,"endTime":2337.453,"body":"Well what would it take?"},{"startTime":2339.46,"endTime":2341.56,"body":"So first of all, it tells you that,"},{"startTime":2341.56,"endTime":2342.97,"body":"I've already mentioned this,"},{"startTime":2342.97,"endTime":2345.22,"body":"that article two of the Rio Convention,"},{"startTime":2345.22,"endTime":2348.16,"body":"which was stabilizing"},{"startTime":2345.22,"endTime":2348.16,"body":"greenhouse gas concentrations,"},{"startTime":2348.16,"endTime":2353.16,"body":"at a level is a sort of"},{"startTime":2348.16,"endTime":2353.16,"body":"problematic target to have,"},{"startTime":2354.55,"endTime":2357.22,"body":"because the world will"},{"startTime":2354.55,"endTime":2357.22,"body":"just continue to warm,"},{"startTime":2357.22,"endTime":2362.22,"body":"for a very long time, many"},{"startTime":2357.22,"endTime":2362.22,"body":"centuries if that's all we do."},{"startTime":2362.712,"endTime":2365.41,"body":"But the other really"},{"startTime":2362.712,"endTime":2365.41,"body":"interesting thing it tells you,"},{"startTime":2365.41,"endTime":2368.47,"body":"is actually, well wait a"},{"startTime":2365.41,"endTime":2368.47,"body":"minute, before we get onto that,"},{"startTime":2368.47,"endTime":2369.303,"body":"I could just ask you,"},{"startTime":2369.303,"endTime":2372.01,"body":"how well this very simple equation,"},{"startTime":2372.01,"endTime":2374.16,"body":"so I've got this very"},{"startTime":2372.01,"endTime":2374.16,"body":"simple equation here."},{"startTime":2375.529,"endTime":2378.37,"body":"Here you are, it may not look that simple,"},{"startTime":2378.37,"endTime":2381.16,"body":"but compared to a climate"},{"startTime":2378.37,"endTime":2381.16,"body":"model, this is pretty simple."},{"startTime":2381.16,"endTime":2383.35,"body":"So it's just got two terms in it."},{"startTime":2383.35,"endTime":2386.71,"body":"The change in the energy flow"},{"startTime":2383.35,"endTime":2386.71,"body":"at the top of the atmosphere,"},{"startTime":2386.71,"endTime":2388.54,"body":"the energy imbalance at"},{"startTime":2386.71,"endTime":2388.54,"body":"the top of the atmosphere"},{"startTime":2388.54,"endTime":2390.01,"body":"and the average energy imbalance,"},{"startTime":2390.01,"endTime":2392.35,"body":"at the top of the atmosphere, okay?"},{"startTime":2392.35,"endTime":2393.95,"body":"Just adding those two things up"},{"startTime":2397.21,"endTime":2400.21,"body":"and comparing that to these dots,"},{"startTime":2400.21,"endTime":2404.02,"body":"which are the outputs of the"},{"startTime":2400.21,"endTime":2404.02,"body":"most advanced climate models,"},{"startTime":2404.02,"endTime":2405.558,"body":"in the world."},{"startTime":2405.558,"endTime":2408.61,"body":"And you can see, you know,"},{"startTime":2408.61,"endTime":2412.27,"body":"they wobble around because"},{"startTime":2408.61,"endTime":2412.27,"body":"of variations in the climate,"},{"startTime":2412.27,"endTime":2413.92,"body":"you know, variable weather and so on."},{"startTime":2413.92,"endTime":2417.343,"body":"But broadly speaking we can understand it."},{"startTime":2419.74,"endTime":2422.98,"body":"Here's the Met office"},{"startTime":2419.74,"endTime":2422.98,"body":"model, which by the way is,"},{"startTime":2422.98,"endTime":2424.72,"body":"you'll notice that by the way,"},{"startTime":2424.72,"endTime":2425.95,"body":"you'll say well there's"},{"startTime":2424.72,"endTime":2425.95,"body":"still some, you know,"},{"startTime":2425.95,"endTime":2427.0,"body":"if you're picky you'd say,"},{"startTime":2427.0,"endTime":2428.71,"body":"well there's a bit of a discrepancy there."},{"startTime":2428.71,"endTime":2430.18,"body":"But hang on, you know,"},{"startTime":2430.18,"endTime":2432.97,"body":"look at the models which"},{"startTime":2430.18,"endTime":2432.97,"body":"we're comparing against."},{"startTime":2432.97,"endTime":2435.31,"body":"And you know, the Met office"},{"startTime":2432.97,"endTime":2435.31,"body":"model actually doesn't shows,"},{"startTime":2435.31,"endTime":2437.02,"body":"no warming at all up until the present."},{"startTime":2437.02,"endTime":2438.58,"body":"Then it takes off like a rocket."},{"startTime":2438.58,"endTime":2439.689,"body":"So, you know,"},{"startTime":2439.689,"endTime":2443.725,"body":"the discrepancies between"},{"startTime":2439.689,"endTime":2443.725,"body":"this very simple equation"},{"startTime":2443.725,"endTime":2447.4,"body":"and these very advanced"},{"startTime":2443.725,"endTime":2447.4,"body":"models are smaller,"},{"startTime":2447.4,"endTime":2450.362,"body":"than the differences between"},{"startTime":2447.4,"endTime":2450.362,"body":"the models themselves."},{"startTime":2450.362,"endTime":2451.72,"body":"I should of course stress,"},{"startTime":2451.72,"endTime":2454.3,"body":"'cause there is somebody"},{"startTime":2451.72,"endTime":2454.3,"body":"from Bayes in the room,"},{"startTime":2454.3,"endTime":2456.19,"body":"that there's many more uses"},{"startTime":2456.19,"endTime":2458.05,"body":"and we don't want to"},{"startTime":2456.19,"endTime":2458.05,"body":"replace the Met office,"},{"startTime":2458.05,"endTime":2460.45,"body":"with a bunch of plastic pipes."},{"startTime":2460.45,"endTime":2464.44,"body":"There's many more uses for climate models,"},{"startTime":2464.44,"endTime":2466.84,"body":"than just predicting global temperature."},{"startTime":2466.84,"endTime":2468.64,"body":"But the point is you can understand,"},{"startTime":2468.64,"endTime":2471.929,"body":"what the climate models tell"},{"startTime":2468.64,"endTime":2471.929,"body":"you about global temperature,"},{"startTime":2471.929,"endTime":2475.09,"body":"you know, without believing every detail,"},{"startTime":2475.09,"endTime":2476.68,"body":"of what the climate model is simulating."},{"startTime":2476.68,"endTime":2478.75,"body":"And that's really important"},{"startTime":2476.68,"endTime":2478.75,"body":"because, you know,"},{"startTime":2478.75,"endTime":2481.27,"body":"people find these climate"},{"startTime":2478.75,"endTime":2481.27,"body":"models quite bewildering."},{"startTime":2481.27,"endTime":2482.74,"body":"They're sort of black boxes,"},{"startTime":2482.74,"endTime":2484.75,"body":"there's lots of ways in"},{"startTime":2482.74,"endTime":2484.75,"body":"which they can go wrong."},{"startTime":2484.75,"endTime":2488.5,"body":"There's lots of things you"},{"startTime":2484.75,"endTime":2488.5,"body":"can nitpick over in them."},{"startTime":2488.5,"endTime":2491.02,"body":"But it's important the"},{"startTime":2488.5,"endTime":2491.02,"body":"fundamental physics,"},{"startTime":2491.02,"endTime":2492.96,"body":"of what drives changes"},{"startTime":2491.02,"endTime":2492.96,"body":"in global temperature,"},{"startTime":2492.96,"endTime":2494.83,"body":"is actually very simple."},{"startTime":2494.83,"endTime":2497.623,"body":"We can capture it with"},{"startTime":2494.83,"endTime":2497.623,"body":"just this simple equation."},{"startTime":2501.16,"endTime":2503.5,"body":"Now comes the punchline."},{"startTime":2503.5,"endTime":2504.333,"body":"Bang on time."},{"startTime":2505.21,"endTime":2508.453,"body":"What will it take to stop global warming?"},{"startTime":2510.67,"endTime":2512.23,"body":"Okay?"},{"startTime":2512.23,"endTime":2516.25,"body":"So you want delta T the"},{"startTime":2512.23,"endTime":2516.25,"body":"change in temperature,"},{"startTime":2516.25,"endTime":2520.0,"body":"over a multi-decade time"},{"startTime":2516.25,"endTime":2520.0,"body":"interval to be, what,"},{"startTime":2520.0,"endTime":2522.31,"body":"if you stopped global warming?"},{"startTime":2522.31,"endTime":2524.83,"body":"Answer is obvious zero, okay?"},{"startTime":2524.83,"endTime":2526.483,"body":"So you want delta T to be zero."},{"startTime":2527.74,"endTime":2528.82,"body":"This is an equation."},{"startTime":2528.82,"endTime":2531.283,"body":"So we've got to get this"},{"startTime":2528.82,"endTime":2531.283,"body":"side to be zero as well."},{"startTime":2532.296,"endTime":2534.013,"body":"And there's two ways to do that."},{"startTime":2535.03,"endTime":2538.72,"body":"One way is to make everything"},{"startTime":2535.03,"endTime":2538.72,"body":"in here zero, yeah?"},{"startTime":2538.72,"endTime":2540.27,"body":"Because zero plus zero is zero."},{"startTime":2541.172,"endTime":2542.56,"body":"The only way we could do that,"},{"startTime":2542.56,"endTime":2546.19,"body":"is to make the average energy flow,"},{"startTime":2546.19,"endTime":2549.25,"body":"due to extra greenhouse gases, zero."},{"startTime":2549.25,"endTime":2551.71,"body":"That means getting greenhouse"},{"startTime":2549.25,"endTime":2551.71,"body":"gas concentrations,"},{"startTime":2551.71,"endTime":2553.003,"body":"back to pre-industrial."},{"startTime":2553.9,"endTime":2555.25,"body":"That would be hard."},{"startTime":2555.25,"endTime":2558.1,"body":"Maybe one day in many"},{"startTime":2555.25,"endTime":2558.1,"body":"thousands of years time,"},{"startTime":2558.1,"endTime":2559.857,"body":"we may get that."},{"startTime":2559.857,"endTime":2562.48,"body":"But there's another way to make this zero."},{"startTime":2562.48,"endTime":2563.353,"body":"What's that?"},{"startTime":2565.918,"endTime":2570.373,"body":"There's two terms here and I"},{"startTime":2565.918,"endTime":2570.373,"body":"want them to add up to zero."},{"startTime":2574.75,"endTime":2577.75,"body":"One of them has to be negative, okay?"},{"startTime":2577.75,"endTime":2580.84,"body":"Now if this average term,"},{"startTime":2580.84,"endTime":2583.12,"body":"that's the average energy imbalance,"},{"startTime":2583.12,"endTime":2585.61,"body":"due to past increases in greenhouse gases,"},{"startTime":2585.61,"endTime":2588.43,"body":"we're kind of stuck with"},{"startTime":2585.61,"endTime":2588.43,"body":"that being positive, yeah?"},{"startTime":2588.43,"endTime":2590.8,"body":"Because greenhouse gases have gone up"},{"startTime":2590.8,"endTime":2593.1,"body":"and they're not going"},{"startTime":2590.8,"endTime":2593.1,"body":"down again anytime soon."},{"startTime":2594.16,"endTime":2595.51,"body":"But that could be negative."},{"startTime":2598.09,"endTime":2600.49,"body":"Do you want to say how"},{"startTime":2598.09,"endTime":2600.49,"body":"much it has to be negative?"},{"startTime":2603.04,"endTime":2605.083,"body":"Well, in order to get it,"},{"startTime":2606.16,"endTime":2608.89,"body":"it's this number is crucial, yep?"},{"startTime":2608.89,"endTime":2613.48,"body":"If the ratio between"},{"startTime":2608.89,"endTime":2613.48,"body":"delta F and F bar delta T"},{"startTime":2613.48,"endTime":2616.06,"body":"or between the change in flow"},{"startTime":2616.06,"endTime":2617.92,"body":"and the average flow multiplied,"},{"startTime":2617.92,"endTime":2621.13,"body":"by the length of a time"},{"startTime":2617.92,"endTime":2621.13,"body":"interval is this rate,"},{"startTime":2621.13,"endTime":2623.83,"body":"then this will average to zero."},{"startTime":2623.83,"endTime":2624.94,"body":"In fact, that's down here."},{"startTime":2624.94,"endTime":2626.14,"body":"Sorry, I was covering it up."},{"startTime":2626.14,"endTime":2629.47,"body":"So if delta F on delta,"},{"startTime":2629.47,"endTime":2630.76,"body":"you'll hopefully you can see that,"},{"startTime":2630.76,"endTime":2634.81,"body":"just rearranging this equation,"},{"startTime":2630.76,"endTime":2634.81,"body":"if delta F on delta T,"},{"startTime":2634.81,"endTime":2637.99,"body":"which is the sort of rate of change,"},{"startTime":2637.99,"endTime":2641.38,"body":"of the fluid flow,"},{"startTime":2641.38,"endTime":2643.87,"body":"divided by the average rate of fluid flow,"},{"startTime":2643.87,"endTime":2647.23,"body":"is equal to negative,"},{"startTime":2647.23,"endTime":2649.48,"body":"this rate so called"},{"startTime":2647.23,"endTime":2649.48,"body":"the rate of adjustment,"},{"startTime":2649.48,"endTime":2650.68,"body":"to constant forcing,"},{"startTime":2650.68,"endTime":2655.68,"body":"which is about 0.3% per"},{"startTime":2650.68,"endTime":2655.68,"body":"year, 3% per decade,"},{"startTime":2656.38,"endTime":2659.35,"body":"then we get no further warming."},{"startTime":2659.35,"endTime":2660.883,"body":"So let's try this experiment."},{"startTime":2663.28,"endTime":2666.043,"body":"This is a simulation where,"},{"startTime":2668.101,"endTime":2673.101,"body":"I'm going to increase the"},{"startTime":2668.101,"endTime":2673.101,"body":"flow over 10 seconds or so"},{"startTime":2673.54,"endTime":2676.663,"body":"and then I'm going to gently decrease it."},{"startTime":2677.68,"endTime":2679.73,"body":"I want you to watch and see what happens."},{"startTime":2681.49,"endTime":2684.85,"body":"After a couple of seconds, okay?"},{"startTime":2684.85,"endTime":2687.61,"body":"You can see it's starting"},{"startTime":2684.85,"endTime":2687.61,"body":"to go up over 10 seconds,"},{"startTime":2687.61,"endTime":2688.443,"body":"it's accelerating."},{"startTime":2688.443,"endTime":2689.41,"body":"Greenhouse gas concentrations,"},{"startTime":2689.41,"endTime":2692.68,"body":"are rising in the atmosphere, okay?"},{"startTime":2692.68,"endTime":2697.68,"body":"And temperature goes up and"},{"startTime":2692.68,"endTime":2697.68,"body":"now it's stopped increasing."},{"startTime":2698.53,"endTime":2700.39,"body":"And if you listen carefully,"},{"startTime":2700.39,"endTime":2705.39,"body":"you can hear that it's slowly"},{"startTime":2700.39,"endTime":2705.39,"body":"slowing down again, yep?"},{"startTime":2705.58,"endTime":2706.75,"body":"Yep?"},{"startTime":2706.75,"endTime":2711.643,"body":"And what's now happening to"},{"startTime":2706.75,"endTime":2711.643,"body":"the level fluid in this pipe?"},{"startTime":2713.947,"endTime":2716.757,"body":"I'm hoping it's not moving, yep?"},{"startTime":2716.757,"endTime":2718.78,"body":"'Cause that's the point."},{"startTime":2718.78,"endTime":2721.838,"body":"Even though the ocean is still warming up"},{"startTime":2721.838,"endTime":2725.53,"body":"and the rate of the pump is going down,"},{"startTime":2725.53,"endTime":2727.69,"body":"that's corresponds to"},{"startTime":2725.53,"endTime":2727.69,"body":"greenhouse gas concentrations,"},{"startTime":2727.69,"endTime":2729.43,"body":"coming down in the atmosphere,"},{"startTime":2729.43,"endTime":2731.8,"body":"these two effects balance each other"},{"startTime":2731.8,"endTime":2733.363,"body":"and we get no further warming."},{"startTime":2734.83,"endTime":2737.59,"body":"That's what we mean by net zero."},{"startTime":2737.59,"endTime":2740.65,"body":"It doesn't mean we've got"},{"startTime":2737.59,"endTime":2740.65,"body":"constant concentrations,"},{"startTime":2740.65,"endTime":2742.63,"body":"of greenhouse gases in the atmosphere."},{"startTime":2742.63,"endTime":2744.25,"body":"It's now switch itself off again."},{"startTime":2744.25,"endTime":2745.42,"body":"It doesn't mean we've got constant,"},{"startTime":2745.42,"endTime":2748.51,"body":"concentrations of greenhouse"},{"startTime":2745.42,"endTime":2748.51,"body":"gases in the atmosphere,"},{"startTime":2748.51,"endTime":2751.39,"body":"it means we're reducing the concentration,"},{"startTime":2751.39,"endTime":2755.38,"body":"fast enough to balance"},{"startTime":2751.39,"endTime":2755.38,"body":"this accumulation of heat,"},{"startTime":2755.38,"endTime":2756.643,"body":"in the deep oceans."},{"startTime":2758.5,"endTime":2761.65,"body":"And how we get concentrations"},{"startTime":2758.5,"endTime":2761.65,"body":"falling at that rate,"},{"startTime":2761.65,"endTime":2765.46,"body":"is of course the subject of"},{"startTime":2761.65,"endTime":2765.46,"body":"our carbon cycle lecture,"},{"startTime":2765.46,"endTime":2769.03,"body":"which will be coming up in"},{"startTime":2765.46,"endTime":2769.03,"body":"a couple of lectures time."},{"startTime":2769.03,"endTime":2772.87,"body":"So there you are, this is, if you like,"},{"startTime":2772.87,"endTime":2775.93,"body":"a good enough model for climate policy,"},{"startTime":2775.93,"endTime":2779.23,"body":"changes in temperature over"},{"startTime":2775.93,"endTime":2779.23,"body":"decade to century time scales,"},{"startTime":2779.23,"endTime":2781.06,"body":"are just how much do you change,"},{"startTime":2781.06,"endTime":2784.21,"body":"the concentrations of greenhouse"},{"startTime":2781.06,"endTime":2784.21,"body":"gases over that period,"},{"startTime":2784.21,"endTime":2785.983,"body":"plus what level are they at?"},{"startTime":2787.026,"endTime":2790.48,"body":"For fast changes, this dominates."},{"startTime":2790.48,"endTime":2793.03,"body":"For slow changes as your"},{"startTime":2790.48,"endTime":2793.03,"body":"approaching equilibrium,"},{"startTime":2793.03,"endTime":2794.98,"body":"this becomes important as well."},{"startTime":2794.98,"endTime":2797.56,"body":"And if you want to know what it"},{"startTime":2794.98,"endTime":2797.56,"body":"takes to get delta T to zero,"},{"startTime":2797.56,"endTime":2799.75,"body":"you have to get these two to balance,"},{"startTime":2799.75,"endTime":2802.87,"body":"which means you have to have"},{"startTime":2799.75,"endTime":2802.87,"body":"declining concentrations,"},{"startTime":2802.87,"endTime":2805.36,"body":"of greenhouse gases in the atmosphere."},{"startTime":2805.36,"endTime":2807.37,"body":"And by the way, for the enthusiasts,"},{"startTime":2807.37,"endTime":2808.93,"body":"here's the gory details,"},{"startTime":2808.93,"endTime":2811.69,"body":"of the whole set of"},{"startTime":2808.93,"endTime":2811.69,"body":"equations that runs this."},{"startTime":2811.69,"endTime":2814.098,"body":"And I'm not going to"},{"startTime":2811.69,"endTime":2814.098,"body":"go through all of that."},{"startTime":2814.098,"endTime":2816.55,"body":"But and for those of you here,"},{"startTime":2816.55,"endTime":2818.92,"body":"this is the sort of stuff"},{"startTime":2816.55,"endTime":2818.92,"body":"you'll do when you're doing,"},{"startTime":2818.92,"endTime":2819.82,"body":"actually you probably won't even do,"},{"startTime":2819.82,"endTime":2821.68,"body":"couple differential"},{"startTime":2819.82,"endTime":2821.68,"body":"equations in further maths."},{"startTime":2821.68,"endTime":2824.523,"body":"You might do, I'm not quite"},{"startTime":2821.68,"endTime":2824.523,"body":"sure, I can't quite remember."},{"startTime":2825.52,"endTime":2830.52,"body":"And that's the this term is"},{"startTime":2825.52,"endTime":2830.52,"body":"that additional energy flow,"},{"startTime":2830.71,"endTime":2831.85,"body":"to the deep ocean,"},{"startTime":2831.85,"endTime":2834.13,"body":"due to the fact that the"},{"startTime":2831.85,"endTime":2834.13,"body":"systems out of equilibrium."},{"startTime":2834.13,"endTime":2836.32,"body":"And by the way, if you think about it,"},{"startTime":2836.32,"endTime":2838.21,"body":"this exact same set of equations,"},{"startTime":2838.21,"endTime":2839.11,"body":"is the set of equations,"},{"startTime":2839.11,"endTime":2841.42,"body":"that governs the fluid in these pipes."},{"startTime":2841.42,"endTime":2844.0,"body":"So it's a nice example of how you can do,"},{"startTime":2844.0,"endTime":2847.963,"body":"coupled differential"},{"startTime":2844.0,"endTime":2847.963,"body":"equations with fluid in pipes."},{"startTime":2849.49,"endTime":2850.81,"body":"Finally, there's one more term,"},{"startTime":2850.81,"endTime":2851.643,"body":"which is just an important one,"},{"startTime":2851.643,"endTime":2853.99,"body":"which I sort of add for completeness."},{"startTime":2853.99,"endTime":2858.34,"body":"This is here, it's the"},{"startTime":2853.99,"endTime":2858.34,"body":"additional energy flow to space,"},{"startTime":2858.34,"endTime":2861.445,"body":"that results from the system"},{"startTime":2858.34,"endTime":2861.445,"body":"being out of equilibrium,"},{"startTime":2861.445,"endTime":2865.12,"body":"for this model to be truly realistic,"},{"startTime":2865.12,"endTime":2869.53,"body":"the length of this pipe"},{"startTime":2865.12,"endTime":2869.53,"body":"would have to somehow adjust,"},{"startTime":2869.53,"endTime":2873.88,"body":"to the pressure difference"},{"startTime":2869.53,"endTime":2873.88,"body":"between these two tubes."},{"startTime":2873.88,"endTime":2876.49,"body":"And we couldn't work out"},{"startTime":2873.88,"endTime":2876.49,"body":"how to do that, okay?"},{"startTime":2876.49,"endTime":2880.51,"body":"So, but if you can maths to the rescue,"},{"startTime":2880.51,"endTime":2881.74,"body":"you can actually rearrange this"},{"startTime":2881.74,"endTime":2884.59,"body":"and discover that satisfies"},{"startTime":2881.74,"endTime":2884.59,"body":"the same equations anyway."},{"startTime":2884.59,"endTime":2886.81,"body":"That's left as an exercise."},{"startTime":2886.81,"endTime":2889.202,"body":"So and by the way, if you're"},{"startTime":2886.81,"endTime":2889.202,"body":"really interested in this,"},{"startTime":2889.202,"endTime":2892.93,"body":"indomitable nerds can go and"},{"startTime":2889.202,"endTime":2892.93,"body":"read a paper free online,"},{"startTime":2892.93,"endTime":2895.72,"body":"net zero science origins and Implications,"},{"startTime":2895.72,"endTime":2897.403,"body":"which has all the maths in it."},{"startTime":2898.3,"endTime":2901.69,"body":"Although I have been told by a colleague,"},{"startTime":2901.69,"endTime":2903.22,"body":"that the maths is somewhat gratuitous"},{"startTime":2903.22,"endTime":2904.72,"body":"and it's perfectly possible"},{"startTime":2903.22,"endTime":2904.72,"body":"to follow the paper,"},{"startTime":2904.72,"endTime":2906.37,"body":"without the maths."},{"startTime":2906.37,"endTime":2908.53,"body":"He was sort of slightly"},{"startTime":2906.37,"endTime":2908.53,"body":"teasing me about the fact,"},{"startTime":2908.53,"endTime":2910.15,"body":"that I put all these questions in there,"},{"startTime":2910.15,"endTime":2911.95,"body":"he felt rather unnecessarily."},{"startTime":2911.95,"endTime":2914.5,"body":"Anyway that's the slow adjustment term,"},{"startTime":2914.5,"endTime":2916.87,"body":"because result as the world warms"},{"startTime":2916.87,"endTime":2918.46,"body":"and heads back to equilibrium,"},{"startTime":2918.46,"endTime":2920.17,"body":"the pattern of warming changes,"},{"startTime":2920.17,"endTime":2921.88,"body":"which changes the efficiency,"},{"startTime":2921.88,"endTime":2925.87,"body":"with which the planet gets"},{"startTime":2921.88,"endTime":2925.87,"body":"sheds energy back into space."},{"startTime":2925.87,"endTime":2928.75,"body":"This is a really important term, sorry,"},{"startTime":2928.75,"endTime":2930.763,"body":"I should remember to switch this off."},{"startTime":2933.82,"endTime":2935.413,"body":"Now that it's done its thing."},{"startTime":2938.26,"endTime":2939.613,"body":"This is a really important time,"},{"startTime":2939.613,"endTime":2943.06,"body":"'cause it adds to the"},{"startTime":2939.613,"endTime":2943.06,"body":"considerable level of uncertainty,"},{"startTime":2943.06,"endTime":2945.85,"body":"we have in where the warming will stop,"},{"startTime":2945.85,"endTime":2948.7,"body":"if we were to hold concentrations"},{"startTime":2945.85,"endTime":2948.7,"body":"of greenhouse gases,"},{"startTime":2948.7,"endTime":2949.99,"body":"at today's level forever."},{"startTime":2949.99,"endTime":2951.85,"body":"But fortunately,"},{"startTime":2951.85,"endTime":2953.02,"body":"there's another option,"},{"startTime":2953.02,"endTime":2955.63,"body":"if we can get greenhouse"},{"startTime":2953.02,"endTime":2955.63,"body":"gas concentrations falling,"},{"startTime":2955.63,"endTime":2958.69,"body":"fast enough we never need"},{"startTime":2955.63,"endTime":2958.69,"body":"to worry about all this."},{"startTime":2958.69,"endTime":2960.16,"body":"And that's really important."},{"startTime":2960.16,"endTime":2962.32,"body":"So the ocean physics behind net zero."},{"startTime":2962.32,"endTime":2966.25,"body":"First of all, how the"},{"startTime":2962.32,"endTime":2966.25,"body":"circulation of the oceans,"},{"startTime":2966.25,"endTime":2967.78,"body":"keeps the deep ocean cold?"},{"startTime":2967.78,"endTime":2971.11,"body":"So the deep ocean is, it's not"},{"startTime":2967.78,"endTime":2971.11,"body":"sort of called by accident,"},{"startTime":2971.11,"endTime":2973.27,"body":"it's kept cold by the fact that,"},{"startTime":2973.27,"endTime":2974.89,"body":"all of the water down in the deep oceans,"},{"startTime":2974.89,"endTime":2976.183,"body":"comes from the Arctic."},{"startTime":2977.8,"endTime":2982.8,"body":"And this slow, we call it"},{"startTime":2977.8,"endTime":2982.8,"body":"the thermohaline circulation,"},{"startTime":2982.84,"endTime":2987.01,"body":"provides that multi"},{"startTime":2982.84,"endTime":2987.01,"body":"century timescale response,"},{"startTime":2987.01,"endTime":2988.87,"body":"that's represented in our little model,"},{"startTime":2988.87,"endTime":2991.99,"body":"by the fat pipe over on the right."},{"startTime":2991.99,"endTime":2995.32,"body":"And just thinking about these two,"},{"startTime":2995.32,"endTime":2997.48,"body":"this sort of simple pipe model,"},{"startTime":2997.48,"endTime":2999.882,"body":"you can realize that just two quantities,"},{"startTime":2999.882,"endTime":3003.21,"body":"the so-called transient"},{"startTime":2999.882,"endTime":3003.21,"body":"climate response to forcing,"},{"startTime":3003.21,"endTime":3004.77,"body":"that's how much it jumps up,"},{"startTime":3004.77,"endTime":3007.62,"body":"when I crank up the speed of the pump"},{"startTime":3007.62,"endTime":3010.8,"body":"and the rate of adjustment"},{"startTime":3007.62,"endTime":3010.8,"body":"to constant forcing,"},{"startTime":3010.8,"endTime":3012.75,"body":"that's the rate at which"},{"startTime":3010.8,"endTime":3012.75,"body":"it continues to rise,"},{"startTime":3012.75,"endTime":3016.5,"body":"when I stop changing"},{"startTime":3012.75,"endTime":3016.5,"body":"the speed of the pump,"},{"startTime":3016.5,"endTime":3020.04,"body":"are enough to understand"},{"startTime":3016.5,"endTime":3020.04,"body":"global temperature changes,"},{"startTime":3020.04,"endTime":3022.44,"body":"on decade to century time scales"},{"startTime":3022.44,"endTime":3026.25,"body":"and to understand what it"},{"startTime":3022.44,"endTime":3026.25,"body":"takes to stop global warming."},{"startTime":3026.25,"endTime":3027.083,"body":"Thank you."},{"startTime":3028.092,"endTime":3030.842,"body":"(crowd applauds)"},{"startTime":3036.402,"endTime":3038.13,"body":"- Thank you so much Professor Alan."},{"startTime":3038.13,"endTime":3039.66,"body":"I've got a couple of questions online,"},{"startTime":3039.66,"endTime":3042.66,"body":"before we go to the room,"},{"startTime":3039.66,"endTime":3042.66,"body":"if that's all right."},{"startTime":3042.66,"endTime":3044.155,"body":"The first one is,"},{"startTime":3044.155,"endTime":3046.62,"body":"does the temperature of the earth's core,"},{"startTime":3046.62,"endTime":3049.89,"body":"have any influence on"},{"startTime":3046.62,"endTime":3049.89,"body":"deep ocean temperature?"},{"startTime":3049.89,"endTime":3054.666,"body":"I eg rather like the way"},{"startTime":3049.89,"endTime":3054.666,"body":"temperature rises in a deep mine."},{"startTime":3054.666,"endTime":3056.97,"body":"- There's a yeah, great question."},{"startTime":3056.97,"endTime":3060.51,"body":"There's a very gentle trickle of energy,"},{"startTime":3060.51,"endTime":3062.28,"body":"into the bottom of the ocean,"},{"startTime":3062.28,"endTime":3065.52,"body":"from geothermal heat in mid ocean ridges."},{"startTime":3065.52,"endTime":3067.26,"body":"You know columns of boiling water,"},{"startTime":3067.26,"endTime":3068.31,"body":"coming out of mid ocean ridges."},{"startTime":3068.31,"endTime":3070.457,"body":"You've probably seen movies of that,"},{"startTime":3070.457,"endTime":3075.12,"body":"but compared to the volume of"},{"startTime":3070.457,"endTime":3075.12,"body":"the ocean itself, it's tiny."},{"startTime":3075.12,"endTime":3077.463,"body":"So and you'll so,"},{"startTime":3078.53,"endTime":3082.47,"body":"if the ocean circulation wasn't happening,"},{"startTime":3082.47,"endTime":3084.84,"body":"it would eventually warm the oceans up."},{"startTime":3084.84,"endTime":3086.7,"body":"So you've got to be careful"},{"startTime":3084.84,"endTime":3086.7,"body":"with numbers like tiny,"},{"startTime":3086.7,"endTime":3089.01,"body":"because you've got to"},{"startTime":3086.7,"endTime":3089.01,"body":"think, well in what context,"},{"startTime":3089.01,"endTime":3090.09,"body":"you know over billions of years,"},{"startTime":3090.09,"endTime":3091.38,"body":"that would warm the oceans up,"},{"startTime":3091.38,"endTime":3092.91,"body":"but it's the oceans are kept cold,"},{"startTime":3092.91,"endTime":3095.085,"body":"by that ocean circulation anyway."},{"startTime":3095.085,"endTime":3098.01,"body":"- Second question I've got from online is,"},{"startTime":3098.01,"endTime":3099.66,"body":"this makes it all seem quite simple."},{"startTime":3099.66,"endTime":3100.98,"body":"Is it really that simple?"},{"startTime":3100.98,"endTime":3103.443,"body":"And does everyone agree that it is simple?"},{"startTime":3105.96,"endTime":3108.99,"body":"- If you want to understand"},{"startTime":3105.96,"endTime":3108.99,"body":"global temperature,"},{"startTime":3108.99,"endTime":3111.0,"body":"then it pretty much is that simple,"},{"startTime":3111.0,"endTime":3116.0,"body":"at least so far the important"},{"startTime":3111.0,"endTime":3116.0,"body":"proviso there so far,"},{"startTime":3117.81,"endTime":3120.45,"body":"the response of global temperature,"},{"startTime":3120.45,"endTime":3123.45,"body":"to global changes in"},{"startTime":3120.45,"endTime":3123.45,"body":"greenhouse gas concentrations,"},{"startTime":3123.45,"endTime":3125.94,"body":"has been remarkably simple."},{"startTime":3125.94,"endTime":3127.92,"body":"And by the way, this again wasn't obvious."},{"startTime":3127.92,"endTime":3131.76,"body":"I remember when I started"},{"startTime":3127.92,"endTime":3131.76,"body":"in this field, you know,"},{"startTime":3131.76,"endTime":3133.92,"body":"when I was doing my doctorate,"},{"startTime":3133.92,"endTime":3138.66,"body":"back in the sort of"},{"startTime":3133.92,"endTime":3138.66,"body":"late 1980s, early 1990s,"},{"startTime":3138.66,"endTime":3140.76,"body":"I remember going to lectures where,"},{"startTime":3140.76,"endTime":3142.29,"body":"you know, people were saying,"},{"startTime":3142.29,"endTime":3143.24,"body":"the university I was at"},{"startTime":3143.24,"endTime":3145.23,"body":"or the university I'm still at actually,"},{"startTime":3145.23,"endTime":3147.6,"body":"people saying, oh, you"},{"startTime":3145.23,"endTime":3147.6,"body":"know, we understand chaos."},{"startTime":3147.6,"endTime":3149.606,"body":"We understand the things"},{"startTime":3147.6,"endTime":3149.606,"body":"are very complicated"},{"startTime":3149.606,"endTime":3151.59,"body":"and it's only these sort"},{"startTime":3149.606,"endTime":3151.59,"body":"of naive geographers,"},{"startTime":3151.59,"endTime":3153.36,"body":"who think that when you ramp"},{"startTime":3151.59,"endTime":3153.36,"body":"up the greenhouse gases,"},{"startTime":3153.36,"endTime":3155.22,"body":"it'll be very simple and it'll follow."},{"startTime":3155.22,"endTime":3157.47,"body":"Anyway, turns out on that score,"},{"startTime":3157.47,"endTime":3158.82,"body":"the geographers are quite right."},{"startTime":3158.82,"endTime":3160.8,"body":"It basically, you crank"},{"startTime":3158.82,"endTime":3160.8,"body":"up gene greenhouse gases,"},{"startTime":3160.8,"endTime":3164.34,"body":"world warmed up in a very"},{"startTime":3160.8,"endTime":3164.34,"body":"predictable way so far."},{"startTime":3164.34,"endTime":3166.17,"body":"We shall see what happens in the future."},{"startTime":3166.17,"endTime":3167.85,"body":"- I have one more question from online,"},{"startTime":3167.85,"endTime":3169.83,"body":"before turning to the"},{"startTime":3167.85,"endTime":3169.83,"body":"room, if you'll forgive me."},{"startTime":3169.83,"endTime":3172.23,"body":"The deep sea is kept cold by the Arctic."},{"startTime":3172.23,"endTime":3174.69,"body":"Does the Antarctic play"},{"startTime":3172.23,"endTime":3174.69,"body":"a role role at all?"},{"startTime":3174.69,"endTime":3175.963,"body":"- Sorry, yes, I should have."},{"startTime":3175.963,"endTime":3178.59,"body":"I should understand Arctic regions,"},{"startTime":3178.59,"endTime":3181.383,"body":"we tend to use the"},{"startTime":3178.59,"endTime":3181.383,"body":"phrase to refer to both."},{"startTime":3181.383,"endTime":3184.8,"body":"Deep water is formed around the Antarctica"},{"startTime":3184.8,"endTime":3186.21,"body":"and also in the North Atlantic."},{"startTime":3186.21,"endTime":3189.569,"body":"So both regions play an important role."},{"startTime":3189.569,"endTime":3190.95,"body":"- [Male Audience Member] Thank you."},{"startTime":3190.95,"endTime":3194.433,"body":"You've talked about"},{"startTime":3190.95,"endTime":3194.433,"body":"politicians obsession with,"},{"startTime":3195.27,"endTime":3198.0,"body":"stabilizing greenhouse emissions"},{"startTime":3198.0,"endTime":3200.97,"body":"and the difficulty of"},{"startTime":3198.0,"endTime":3200.97,"body":"explaining climate science,"},{"startTime":3200.97,"endTime":3203.31,"body":"to politicians is that just a,"},{"startTime":3203.31,"endTime":3205.41,"body":"another tragic feature"},{"startTime":3203.31,"endTime":3205.41,"body":"of the two cultures,"},{"startTime":3205.41,"endTime":3208.08,"body":"that politicians learn humanities"},{"startTime":3208.08,"endTime":3210.45,"body":"and journalists then"},{"startTime":3208.08,"endTime":3210.45,"body":"don't understand basic,"},{"startTime":3210.45,"endTime":3211.863,"body":"scientific concepts?"},{"startTime":3213.113,"endTime":3214.696,"body":"- To be fair,"},{"startTime":3214.696,"endTime":3218.85,"body":"the political community got on board,"},{"startTime":3218.85,"endTime":3221.55,"body":"net zero remarkably quickly."},{"startTime":3221.55,"endTime":3224.13,"body":"I mean, you know, we did this work,"},{"startTime":3224.13,"endTime":3226.17,"body":"we established that it wasn't enough,"},{"startTime":3226.17,"endTime":3228.03,"body":"to stabilize concentrations."},{"startTime":3228.03,"endTime":3231.18,"body":"You actually had to get"},{"startTime":3228.03,"endTime":3231.18,"body":"concentrations going down."},{"startTime":3231.18,"endTime":3234.75,"body":"That work was done in the late 2000s."},{"startTime":3234.75,"endTime":3235.71,"body":"And the Paris agreement,"},{"startTime":3235.71,"endTime":3237.51,"body":"which essentially acknowledges that"},{"startTime":3237.51,"endTime":3242.01,"body":"and moves on from that"},{"startTime":3237.51,"endTime":3242.01,"body":"stabilization framing of Rio,"},{"startTime":3242.01,"endTime":3244.02,"body":"was signed in 2015."},{"startTime":3244.02,"endTime":3249.02,"body":"So, you know yes it's a"},{"startTime":3244.02,"endTime":3249.02,"body":"perpetual struggle communicating,"},{"startTime":3249.3,"endTime":3250.68,"body":"but it can work."},{"startTime":3250.68,"endTime":3252.06,"body":"And on that occasion,"},{"startTime":3252.06,"endTime":3256.053,"body":"I think the politicians did"},{"startTime":3252.06,"endTime":3256.053,"body":"take this on quite quickly."},{"startTime":3257.04,"endTime":3261.27,"body":"That said, we have sort of"},{"startTime":3257.04,"endTime":3261.27,"body":"keep reminding people of this,"},{"startTime":3261.27,"endTime":3266.067,"body":"because as we'll come onto"},{"startTime":3261.27,"endTime":3266.067,"body":"in the carbon cycle nature,"},{"startTime":3269.659,"endTime":3273.24,"body":"there's an increasing tendency"},{"startTime":3269.659,"endTime":3273.24,"body":"these days for countries"},{"startTime":3273.24,"endTime":3274.59,"body":"and companies and so on,"},{"startTime":3274.59,"endTime":3276.9,"body":"to sort of declare they got to net zero,"},{"startTime":3276.9,"endTime":3279.69,"body":"when they're no longer,"},{"startTime":3279.69,"endTime":3281.22,"body":"when the sort of balance"},{"startTime":3279.69,"endTime":3281.22,"body":"in the atmosphere,"},{"startTime":3281.22,"endTime":3283.56,"body":"when effectively their activities,"},{"startTime":3283.56,"endTime":3286.28,"body":"would stabilize greenhouse"},{"startTime":3283.56,"endTime":3286.28,"body":"gas concentrations,"},{"startTime":3286.28,"endTime":3287.113,"body":"of the atmosphere."},{"startTime":3287.113,"endTime":3287.946,"body":"You have to remind 'em no,"},{"startTime":3287.946,"endTime":3289.29,"body":"that that's not what we meant by net zero."},{"startTime":3289.29,"endTime":3291.15,"body":"You need to go beyond that."},{"startTime":3291.15,"endTime":3293.28,"body":"We'll I'll explain more about that,"},{"startTime":3293.28,"endTime":3294.75,"body":"in the carbon cycle lecture,"},{"startTime":3294.75,"endTime":3296.67,"body":"but it's still topical, therefore."},{"startTime":3296.67,"endTime":3298.59,"body":"- [Female Speaker] I"},{"startTime":3296.67,"endTime":3298.59,"body":"understand that temperatures,"},{"startTime":3298.59,"endTime":3303.57,"body":"in Kodiak Island in Alaska"},{"startTime":3298.59,"endTime":3303.57,"body":"in 1st of January, 2021,"},{"startTime":3303.57,"endTime":3305.37,"body":"reached 19 degrees C."},{"startTime":3305.37,"endTime":3308.43,"body":"The Antarctic has been"},{"startTime":3305.37,"endTime":3308.43,"body":"apparently recorded,"},{"startTime":3308.43,"endTime":3311.91,"body":"as having temperatures at"},{"startTime":3308.43,"endTime":3311.91,"body":"30 degrees above average."},{"startTime":3311.91,"endTime":3314.67,"body":"How is this affecting deep water,"},{"startTime":3314.67,"endTime":3318.12,"body":"cold water formation and the"},{"startTime":3314.67,"endTime":3318.12,"body":"the hairline circulation?"},{"startTime":3318.12,"endTime":3319.484,"body":"- Yes, yeah."},{"startTime":3319.484,"endTime":3320.91,"body":"- [Female Speaker] How quickly."},{"startTime":3320.91,"endTime":3322.563,"body":"- Yeah, no so obviously,"},{"startTime":3323.55,"endTime":3326.64,"body":"the changes in the"},{"startTime":3323.55,"endTime":3326.64,"body":"temperature in these regions,"},{"startTime":3326.64,"endTime":3328.35,"body":"have a particularly importance,"},{"startTime":3328.35,"endTime":3332.91,"body":"because the ocean will be"},{"startTime":3328.35,"endTime":3332.91,"body":"remembering those changes,"},{"startTime":3332.91,"endTime":3334.56,"body":"for hundreds of years."},{"startTime":3334.56,"endTime":3336.24,"body":"If you warm up in a given year,"},{"startTime":3336.24,"endTime":3338.94,"body":"if you warm up the Labrador Sea,"},{"startTime":3338.94,"endTime":3342.33,"body":"then the water that enters the deep ocean,"},{"startTime":3342.33,"endTime":3345.54,"body":"from the Labrador Sea will"},{"startTime":3342.33,"endTime":3345.54,"body":"remember that temperature,"},{"startTime":3345.54,"endTime":3346.56,"body":"for centuries."},{"startTime":3346.56,"endTime":3349.26,"body":"So these changes really matter."},{"startTime":3349.26,"endTime":3354.26,"body":"Even if they only happen"},{"startTime":3349.26,"endTime":3354.26,"body":"in a given season,"},{"startTime":3354.504,"endTime":3356.94,"body":"the earth will remember"},{"startTime":3354.504,"endTime":3356.94,"body":"them for a long time."},{"startTime":3356.94,"endTime":3359.103,"body":"So and they're not, you know,"},{"startTime":3360.56,"endTime":3363.24,"body":"they're happening more and more often,"},{"startTime":3363.24,"endTime":3364.92,"body":"so exactly it's building up."},{"startTime":3364.92,"endTime":3367.563,"body":"So yeah, no, it's very important."},{"startTime":3367.563,"endTime":3370.35,"body":"This of course is why we need"},{"startTime":3367.563,"endTime":3370.35,"body":"complicated climate models,"},{"startTime":3370.35,"endTime":3374.82,"body":"as well as, you know, fluid in pipes,"},{"startTime":3374.82,"endTime":3378.84,"body":"in order to understand how"},{"startTime":3374.82,"endTime":3378.84,"body":"those changes in these regions,"},{"startTime":3378.84,"endTime":3381.4,"body":"actually affect the penetration of heat,"},{"startTime":3384.93,"endTime":3387.09,"body":"into the ocean depths."},{"startTime":3387.09,"endTime":3389.58,"body":"And of course a big worry"},{"startTime":3389.58,"endTime":3394.47,"body":"and a point that I will look"},{"startTime":3389.58,"endTime":3394.47,"body":"at later in these lectures"},{"startTime":3394.47,"endTime":3397.68,"body":"or we may have to delve"},{"startTime":3394.47,"endTime":3397.68,"body":"into it more later on,"},{"startTime":3397.68,"endTime":3401.4,"body":"in the, because it's"},{"startTime":3397.68,"endTime":3401.4,"body":"involves even more maths,"},{"startTime":3401.4,"endTime":3405.51,"body":"is the danger that if you"},{"startTime":3401.4,"endTime":3405.51,"body":"mess with the system enough,"},{"startTime":3405.51,"endTime":3410.04,"body":"then you could actually affect"},{"startTime":3405.51,"endTime":3410.04,"body":"the ocean circulation itself."},{"startTime":3410.04,"endTime":3411.84,"body":"And for example,"},{"startTime":3411.84,"endTime":3414.78,"body":"if you were to shut down the"},{"startTime":3411.84,"endTime":3414.78,"body":"entire ocean circulation,"},{"startTime":3414.78,"endTime":3417.54,"body":"you'd have a huge impact on climate,"},{"startTime":3417.54,"endTime":3419.532,"body":"which would be very difficult to reverse."},{"startTime":3419.532,"endTime":3422.13,"body":"That's not predicted"},{"startTime":3419.532,"endTime":3422.13,"body":"to happen anytime soon."},{"startTime":3422.13,"endTime":3423.933,"body":"But as I say, you know,"},{"startTime":3424.89,"endTime":3426.96,"body":"just 'cause it doesn't happen in models,"},{"startTime":3426.96,"endTime":3428.73,"body":"doesn't mean it can't"},{"startTime":3426.96,"endTime":3428.73,"body":"happen in the real world."},{"startTime":3428.73,"endTime":3430.62,"body":"It's certainly a worry and"},{"startTime":3428.73,"endTime":3430.62,"body":"one which we're watching."},{"startTime":3430.62,"endTime":3431.79,"body":"And one of the reasons,"},{"startTime":3431.79,"endTime":3434.19,"body":"why people are particularly concerned,"},{"startTime":3434.19,"endTime":3437.61,"body":"about these huge changes we're"},{"startTime":3434.19,"endTime":3437.61,"body":"seeing in arctic regions,"},{"startTime":3437.61,"endTime":3439.723,"body":"is 'cause we know not only are they,"},{"startTime":3439.723,"endTime":3442.35,"body":"a very sort of sensitive indicator region,"},{"startTime":3442.35,"endTime":3444.54,"body":"but they play an absolutely vital role"},{"startTime":3444.54,"endTime":3449.37,"body":"in important in what"},{"startTime":3444.54,"endTime":3449.37,"body":"controls our global climate."},{"startTime":3449.37,"endTime":3454.37,"body":"So, you know, the fact"},{"startTime":3449.37,"endTime":3454.37,"body":"that every liter of water,"},{"startTime":3454.53,"endTime":3456.141,"body":"in the earth's oceans,"},{"startTime":3456.141,"endTime":3458.43,"body":"over the vast bulk of the depth,"},{"startTime":3458.43,"endTime":3461.47,"body":"has probably got there via the Arctic,"},{"startTime":3461.47,"endTime":3465.9,"body":"tells you just how important"},{"startTime":3461.47,"endTime":3465.9,"body":"changes in the or Antarctica,"},{"startTime":3465.9,"endTime":3468.15,"body":"tells you just how important"},{"startTime":3465.9,"endTime":3468.15,"body":"for future climate,"},{"startTime":3468.15,"endTime":3472.117,"body":"changes today in the"},{"startTime":3468.15,"endTime":3472.117,"body":"Arctic and Antarctica are."},{"startTime":3473.28,"endTime":3475.71,"body":"- Thank you so much, professor Allen."},{"startTime":3475.71,"endTime":3477.45,"body":"Professor Allen's next lecture,"},{"startTime":3477.45,"endTime":3480.0,"body":"is going to be on the 7th of March."},{"startTime":3480.0,"endTime":3483.15,"body":"- Yes and in view of the fact that,"},{"startTime":3483.15,"endTime":3487.27,"body":"so in a slight shift to the program"},{"startTime":3488.19,"endTime":3491.31,"body":"and earlier we were going to sort of,"},{"startTime":3491.31,"endTime":3493.02,"body":"work through the science"},{"startTime":3493.02,"endTime":3497.25,"body":"and then come back to the"},{"startTime":3493.02,"endTime":3497.25,"body":"policy in the final lecture."},{"startTime":3497.25,"endTime":3498.93,"body":"But because we got an energy bill,"},{"startTime":3498.93,"endTime":3500.88,"body":"in front of parliament at the moment"},{"startTime":3500.88,"endTime":3504.179,"body":"and also because I felt having"},{"startTime":3500.88,"endTime":3504.179,"body":"got through this lecture,"},{"startTime":3504.179,"endTime":3507.03,"body":"that you might want to"},{"startTime":3504.179,"endTime":3507.03,"body":"break from the algebra"},{"startTime":3507.03,"endTime":3509.58,"body":"and get back to politics."},{"startTime":3509.58,"endTime":3513.51,"body":"We'll talk about what"},{"startTime":3509.58,"endTime":3513.51,"body":"the UK is trying to do,"},{"startTime":3513.51,"endTime":3514.53,"body":"to get to net zero"},{"startTime":3514.53,"endTime":3517.05,"body":"and what we could put"},{"startTime":3514.53,"endTime":3517.05,"body":"into the energy bill,"},{"startTime":3517.05,"endTime":3520.32,"body":"to make it happen in the next lecture."},{"startTime":3520.32,"endTime":3524.37,"body":"So we'll sort of get stuck into,"},{"startTime":3524.37,"endTime":3526.637,"body":"some of the policy implications,"},{"startTime":3526.637,"endTime":3530.73,"body":"of the need for net zero"},{"startTime":3526.637,"endTime":3530.73,"body":"next time and then we'll,"},{"startTime":3530.73,"endTime":3535.73,"body":"but don't worry the plastic"},{"startTime":3530.73,"endTime":3535.73,"body":"pipes will make a reappearance,"},{"startTime":3535.905,"endTime":3538.44,"body":"in the follow in the last two lectures,"},{"startTime":3538.44,"endTime":3541.26,"body":"when we get onto"},{"startTime":3538.44,"endTime":3541.26,"body":"understanding the carbon cycle"},{"startTime":3541.26,"endTime":3543.57,"body":"and what it'll take to get,"},{"startTime":3543.57,"endTime":3545.01,"body":"atmospheric concentration"},{"startTime":3543.57,"endTime":3545.01,"body":"of the greenhouse gases,"},{"startTime":3545.01,"endTime":3547.353,"body":"going down fast enough"},{"startTime":3545.01,"endTime":3547.353,"body":"to stop global warming."},{"startTime":3548.55,"endTime":3550.11,"body":"So see you on 7th of March."},{"startTime":3550.11,"endTime":3551.85,"body":"- Thank you so much Professor Allen."},{"startTime":3551.85,"endTime":3554.6,"body":"(crowd applauds)"}]}