Acoustics and Climate Change

The impact of climate change on the field of acoustics is multifold. Researchers not only use acoustics to better understand changes to the environment, they also must consider how climate change impacts standard research practices. In this episode, we talk to three of the guest editors of the recent Special Issue on Climate Change: How the Sound of the Planet Reflects the Health of the Planet-- Megan Ballard (University of Texas at Austin), Edward Walsh (VA Loma Linda Healthcare), and Lauren Freeman (Naval Undersea Warfare Center Division Newport). 

Read all the articles from the special issue here!

Read more from The Journal of the Acoustical Society of America (JASA).
Learn more about Acoustical Society of America Publications.

Music Credit: Min 2019 by minwbu from Pixabay. 

Transcript

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Kat Setzer (00:25)

The impact of climate change on the field of acoustics is multifold. Researchers not only use acoustics to better understand changes to the environment, they also must consider how climate change impacts standard research practices. Today we're going to talk about a special issue that's actually been a couple years in the making, The Special Issue on Climate Change: How the Sound of the Planet Reflects the Health of the Planet, which covers the very diverse impacts of climate change on the field of acoustics. With me are three of the guest editors of the special issue: Megan Ballard, Edward Walsh, and Lauren Freeman. Thank you all for taking the time to speak with me today.

Megan Ballard (00:57)

Hey, happy to be here.

Edward Walsh (00:59)

Indeed.

Kat Setzer (00:59)

Well, so first just tell us a bit about your research backgrounds.

Megan Ballard (01:03)

I can go first. My name is Megan, as you said. I'm a research scientist at the University of Texas at Austin ,and I'm studying underwater acoustics. My research has taken me from deep Arctic environments to shallow subtropical estuaries and a lot of places in between. Along the way I've become really interested in how the ocean environment shapes the way sound travels, from the physical properties of the water column to the seafloor and the sea surface. And I also use sound itself as a tool to learn about the ocean using acoustic measurements to infer things like temperature, structure, and ecosystem dynamics. I'm especially interested in how the changing environmental conditions are changing the ocean and how acoustics can help us observe and better understand these changes over time.

Edward Walsh (01:49)

I'll be happy to go next. First, I have to start by saying my research background is completely unrelated to climate change. A large fraction of the early portion of my career was centered on auditory neurophysiology studies, especially in a developmental context. I've also made extensive use of evoked potentials and inner-ear otoacoustic emissions to assess auditory function in both normal and noise-exposed animals. And in more recent years, we've devoted a considerable portion of our work to studies centered on the auditory capabilities and the acoustical characteristics of vocalizations produced by exotic mammals, like tigers and clouded leopards, as well as exotic birds, like bald and golden eagles. I currently run the auditory and neurobiology lab at the VA hospital in Loma Linda, California, where we are developing a non-human animal model of blast-induced traumatic brain injury, with the goal of using that model to develop treatment and mitigation strategies.

Lauren Freeman (02:48)

Awesome. I’ll close out and I learned something new about Ed and Megan through this. So I'm really glad that we're doing this together. So I'm Lauren Freeman. I am a senior scientist for the Navy. I work at a lab in Newport, Rhode Island, and I run the Navy Soundscapes Lab where we explore ambient noise in all sorts of underwater environments, but I'm particularly focused on places that are very dynamic, that have a lot of change. So I'm doing a lot of work now in the Arctic as well as in shallow water, which is what we'll be talking a little bit more about today. And I would call my primary expertise in biological soundscapes in the kinds of underwater noises that are coming from fish and invertebrates like shrimps, crabs, lobsters. But I do work with all types of underwater sounds. I actually came to acoustics a little bit later in my career. I studied oceanography for my PhD at Scripps, and my focus was on climate science and biological oceanography. I was actually looking at climate change impacts on coral reef ecosystems. And through that, I had the chance to join a NOAA monitoring crews in the Hawaiian islands, and I also got a student grant to fund some research. And I put together a data set that went across the whole Hawaiian island chain, thinking I was going to be looking at climate effects on coral reefs, but what I wound up eventually discovering is this really incredible interplay between how the health of coral reefs is reflected in their soundscape. So I started publishing on that and over time, because acoustics is such an amazing community, and because I work for the Navy, I became closer and more closely tied to this research and to this community.

Kat Setzer (04:25)

Right, right. Well it sounds like you guys come from a good variety of backgrounds, both underwater and over water, out of water? So how did this special issue come about?

Megan Ballard (04:34)

So this special issue actually got its start in the Panel of Public Policy, which was chaired by Ed at the time, and I was a member of the panel. So the topic of climate change came up and then really seeking to understand how climate change and acoustics were relevant to one another, we decided to have a special session on climate change and acoustics at the Chicago meeting, which took place in May of 2023. This was a very successful session. We had a lot of really interesting talks. It was chaired by myself, Ed, and Laura Kloepper. And we were really encouraged by the amount of insightful work. And so we decided to pursue the joint special issue in JASA and JASA EL that we're here to talk to you about today. 

And so in addition to Lauren and Ed and myself, YT Lin and Daniel Bloomstein also joined us as associate editors for the special issue. 

So we did eventually make a public policy statement for the ASA, and that was approved at the recent ASA meeting in May of 2026 in Philadelphia, and it has just recently been published on the ASA website. And if you want, I can read the statement for you. 

Kat Setzer (05:51)

Yeah, absolutely.

Megan Ballard (05:52)

Okay, here I go. So “The Acoustical Society of America affirms that climate change is measurably altering environmental soundscapes across oceans, land and air with important implications for ecosystem health and human activities. Because many species depend on sound for essential biological functions, these changes can signal a broader environmental disruption. The ASA's policy position is that the acoustical science and technology play a critical role in monitoring and understanding climate-driven environmental change. Accordingly, the ASA supports the development and application of accurate, reliable, and cost-effective acoustic measurement technologies and it encourages sustained research that uses sound to observe ecosystems, assess climate impacts, and inform evidence-based responses to a changing planet.”

Kat Setzer (06:50)

Woo, that's very exciting. So in your in your introduction to the special issue, you mentioned that acoustics research is both being impacted by changes in the environment, while also becoming a useful tool for observing and understanding these changes. How so?

Megan Ballard (07:02)

Yes. We point out that acoustics has kind of a two-way relationship with climate change. On the one hand, it's being directly affected by changes in the environment. So things like temperature, ocean circulation, sea ice, and atmospheric conditions shift. They also change how sound travels and what soundscapes look like. That can impact everything from natural acoustic environments to the performance of systems and the way we rely on them for communication and monitoring.

At the same time, those sensitivities are exactly what make acoustics so useful for studying climate change. Because sound responds to environmental conditions, we can use acoustic techniques to track things like ocean temperature, sea ice dynamics, and even ecosystem activity over long periods. Methods like ocean acoustic tomography or passive soundscape monitoring give us a way to observe changes that are otherwise hard to measure, especially across large areas and long time scales.

Kat Setzer (08:01)

So the research in this issue covered some pretty diverse fields. Let's start with ocean acoustics. We actually did an episode recently about one of the articles in this area regarding acoustic transmissions in the Arctic. How are ocean acoustic propagation and tomography being used in the efforts to understand climate change?

Megan Ballard (08:17)

So underwater acoustic tomography in the Arctic Ocean is a powerful method for monitoring large-scale changes in temperature, stratification, and circulation in a region where conventional measurements are sparse and challenging. By transmitting low-frequency sound across long distances beneath the ice, underwater acoustic tomography exploits the sensitivity of sound speed to temperature and salinity and to infer basin scale variations in heat content and circulation.

In the Arctic, where rapid warming and increased freshwater input from sea ice melt and river discharge are altering ocean structure. Underwater acoustic tomography provides a unique integrative view of how these changes evolve over time. 

The Arctic is also experiencing some of the fastest warming on Earth, a phenomenon that's known as Arctic amplification. Temperatures in the region are rising roughly two to four times faster than the global average driven by feedback such as sea ice loss, which reduces surface reflectivity and enhances heat absorption. This rapid warming is accompanied by increased freshwater input from melting sea ice, glaciers, river discharge, leading to significant changes in stratification and ocean circulation. These Arctic changes have important implications for the AMOC. AMOC stands for Atlantic Meridional Overturning Circulation. The Arctic acts as an upstream source of freshwater input to the North Atlantic. Increased freshwater export can reduce the density of surface waters in regions where deep water formation forms, and the potential weakening of the sinking branch of the AMOC. Because the AMOC strength depends on density gradients and heat transport, Arctic-driven changes in temperature and salinity can influence its stability. So a slowdown in the AMOC would have widespread climate implications, particularly in the North Atlantic region, with less warm water transported northwards, parts of Europe could experience cooling despite ongoing global warming, while sea levels across the US East Coast could rise due to changes in ocean circulation. It could also disrupt global weather patterns, shifting rainfall belts and affecting monsoons, leading to drought in some regions and increased flooding in others. In addition, changes in ocean temperature and circulation would impact marine ecosystems and fisheries, while feedback from melting Arctic ice and increased freshwater input would further weaken the system. Overall, even a gradual AMOC slowdown has the potential to significantly alter regional and global climate patterns. 

Underwater acoustic tomography contributes to understanding this process by providing continuous basin scale measurements of how heat and fresh water are redistributed across the Arctic Ocean. The article by Matt Dzieciuch, Hanne Sagen, and Peter Worcester in our special issue set out to compare new acoustic travel time estimates from the recent US-Norwegian Coordinated Arctic Acoustic Tomography Experiment, which was known as CAATEX, with measurements from the TAP experiment which took place in 1994. However, the large travel time uncertainty associated with the TAP measurements precluded definitive comparisons. Nonetheless, CAATEX demonstrated that long-range acoustic transmissions provide precise year-long measurements of large-scale ocean sound speed, which is related to temperature, and its variability under the ice. 

So a bit about what's next. Five years since CAATEX’ ongoing work seeks to couple underwater acoustic tomography measurements with other oceanographic measurements for use in ocean circulation models. Additionally, the US-Norwegian group has two sister projects which are ongoing in the eastern Arctic, and they were recovering the moorings this August to set up a new baseline for a different part of the Arctic. They then hope to redeploy and keep the underwater acoustic tomography measurements going. The long-term deployment of sources will also provide geo-positioning system for underwater navigation for gliders and other submerged autonomous vehicles.

Kat Setzer (12:31)

That sounds super, super useful. And as I mentioned to folks, we have an episode about Matt Dzieciuch’s, Hanne Sagen, and Peter Worcester's article. So if you are interested in this topic, you can listen to that. Okay, so related to oceans are marine mammals. How are ocean conditions impacting our underwater neighbors, and how is acoustics being used to understand the impact on marine mammals?

Lauren Freeman (12:52)

So Megan set this up really well with just the overarching theme of this issue and how there's this interplay of multiple factors, both the environment is changing and then the behavior of the animals are also changing. So first of all, the environment itself is changing and that means you're potentially getting different behaviors, which could mean that animals are at different depths, 6hey could be going further north or south, or they could even be going further east or west to try to get to the ideal ocean environment for themselves. And I say “animals” because this could be our whales, dolphins, and seals, but it could also be the things that they're eating. So if their prey are shifting due to ocean chemistry or ocean temperatures, then the marine mammals still want to be able to eat those prey, so they're going to have to adjust their behavior as well. So there's quite a bit of biogeography tied into this question that's being affected by climate change. 

In addition to that, we've got some places where the ocean itself is changing the way that sound propagates. And again, Megan, it's such a nice job of setting this up that I'm not gonna hammer into it too far. But what that means is that whales, dolphins, seals, marine mammals that use acoustics to communicate with each other may not be able to communicate in the way that they're used to. It could mean that their calls are traveling further than they intended and they're giving away their location of things that might want to eat them, or it could mean that they think they're talking to their friends or neighbors or, you know, the lady whale that they wanted to get in touch with, and maybe that's not getting through because there's some different layering going on in the ocean that's affecting those transmission paths.

Kat Setzer (14:27)

Yeah.

Lauren Freeman (14:34)

So we have a couple of papers on toothed whales who actually use acoustics to find their food. And we talked about how the food might be in a different place, but we also talked about how the changing ocean environment changes how sound travels. And so that's leading to very real effects on the ability of things like sperm whales and killer whales to forage and find prey. So we've got a really nice study from the University of New Hampshire looking at the Bering Sea and then from NATO CMRE looking at sperm whales near Svalbard on that particular topic that are both in a special issue.

So in addition to the actual pathways that sound follows in the ocean, we also have new types of sounds that are being introduced by climate change activities, particularly in the Arctic. So we have a really neat paper that I would encourage you to check out showing that ice generated sound, so the sound from the sea ice, believe it or not, that is a thing, is masking vocalizations from bearded seals. So it's making it harder for them to talk to each other, to find each other, and again, to go about their day and do what they need to do. So it's really upending a lot of different ways that marine mammals go about their life.

Kat Setzer (15:49)

So what acoustics research is being done in terms of understanding changes to coral reefs and seagrass meadows?

Lauren Freeman (15:55)

I can start talking a little bit about coral reefs and I shared a tiny bit about this in my background. So for a bit over decade, the acoustics community and the coral reef community have been showing through scientific publication, through studies and data analysis, that there's a really nice link between acoustic soundscapes and coral reef health. And you can in fact describe the health of a coral reef from its acoustics, which is really cool in and of itself, but that's an invaluable tool when we start to think about the kinds of effects that climate change are going to have on coral reefs and on more broadly ocean ecosystems. 

So my lab shared a study in this special issue that leverages a number of long-term monitoring sites that we have set up. And because we have those covering several years now, we're actually able to show a linkage between the ocean temperature and the amount of sound being produced, which was quite interesting. And I'm not talking about marine mammals now; I'm talking about fish and little invertebrates, things like crabs and shrimp. So all cold-blooded animals. And there's a kind of logical ecological theory here that a cold-blooded animal would be more active when their environment was warmer, when their ambient temperature was warmer, and that level of activity increasing could potentially lead to an increased production in sound as well. So we were really excited to see the data come together so nicely. Sometimes when you collect data over a long period of time, you kind of are wondering why you're still doing it. And, you know, why do you keep investing in this? So when you're able to look at it and see something new like that, that is really exciting. 

Kat Setzer (17:31)

Okay, okay. So it's like snapping shrimp are getting snappier or that kind of thing?

Lauren Freeman (17:34)

Snapping shrimp are getting snappier, exactly.

Kat Setzer (17:36)

Okay. Got it.

Lauren Freeman (17:39)

Aran Mooney also put out a really nice study that's in this special issue highlighting the use of acoustics for coral larval recruitment, which is yet another element of how acoustics interplay with coral reef ecology. And we had another great paper in the special issue led by Seth McCannan using convolutional neural networks to detect fish calls in coral reefs. And yet again, broadening our ability to understand reefs acoustically and also highlighting the breadth of work that we're doing in underwater acoustics on coral reef ecosystems.

Megan Ballard (18:11)

And I can say a few words about seagrass, 'cause that's where my own research has come into this. So acoustic techniques have also been applied for monitoring ecosystem health in seagrass meadows. And my group has been studying in the acoustical characteristics of seagrass meadows for over ten years, and we actually have two papers in this special issue related to seagrass. 

If you don't know much about seagrass, they occur worldwide, typically in the inner tidal zone, but places where enough sunlight reaches the seabed for the seagrass to photosynthesize, so they're in pretty shallow water. They are also highly important to ecosystems because they provide a habitat and nursery ground for many marine species. They stabilize sediments, improve water quality, and play a key role in carbon cycling by capturing and storing significant amounts of blue carbon in their biomass in the underlying sediments.

However, seagrass meadows are declining globally and they are among the most threatened ecosystems on Earth. The most common indice for monitoring seagrass meadows is dissolved oxygen, which can be used to estimate and in situ rates of photosynthesis, respiration, and net ecosystem production. However, the low solubility of oxygen often results in the formation of bubbles, particularly in warm, shallow waters, with high rates of primary production and respiration. And since oxygen saturation is common in seagrass meadows, the accuracy of DO measurements of photosynthesis is limited to low light conditions, so only in the early morning hours. On the other hand, underwater acoustic propagation is very sensitive to the presence of bubbles ,and acoustic transmission loss measurements have been used to assess oxygen production in seagrass meadows with high temporal resolution.

And additionally, the detachment of air bubbles from seagrass leaves itself is an important contributor to the ambient soundscape. 

So as I mentioned, we have two papers. In the first one we reported on the daily seasonal and interannual variations in transmission loss in ambient sound, examined during a two-year experiment conducted in a shallow subtropical estuary on the Texas coast. We compared direct measurements of photosynthetic bubble production using gas collected in inverted funnels with our acoustic estimates to develop an empirical relationship between TL and gas flux. And we also show transmission loss caused gas encapsulated within the seagrass, so we can measure seagrass growth patterns using our acoustic measurements as well. And then building on this data set, we had a second paper where we applied Bayesian inference to estimate the above-ground biomass of seagrass, which showed its seasonal pattern, and it compared favorably with direct measurements of biomass from cores. 

And then looking forward, we recently completed a year-long experiment using only passive acoustic measurements to study the heterogeneity of a seagrass meadow by comparing acoustic measurements across six different sites. The study focused on using acoustic measurements to quantify the non-dissolved contribution of oxygen to obtain more accurate measurements of net ecosystem productivity and then relate that to the amount of carbon that's being sequestered within the sediment matrix.

Kat Setzer (21:29)

Interesting. I don't think I ever realized what, like ,unsung heroes the seagrass meadows were of the underwater environment, you know?

Megan Ballard (21:34)

Mm-hmm.

Kat Setzer (21:38)

So the impacts of pile driving also came up in the special issue, particularly with regards to the development of wind farms. How is the noise and vibration associated with pile driving affecting the surrounding marine environments?

Lauren Freeman (21:50)

Great question, Kat. So these are a couple of studies out of Aran Mooney’s lab at Woods Hole Oceanographic Institution. And they're really interesting addition to the special issue because they're highlighting an aspect of life on Earth in the 2020s, which is exploration of new energy production modalities, including offshore wind. Here in Rhode Island, where I'm located, offshore wind is a very hot topic. And there are people who have very strong opinions on both sides of it, ranging from people that really dislike the visual aesthetic of the wind farms, to fishermen that find that the installations are providing structure and habitat that's leading to more reliable catches in those locations for them. So it's something we hear about quite a bit here, and I can certainly understand why our colleagues over at Woods Hole were interested in studying this further. 

In general, we in the United States are installing pile-based offshore wind, which means you have to put in big pilings. So there's heavy pile driving. And that's introducing quite a lot of acoustic energy into the environment, similar to pile driving for oil and gas or coastal infrastructure. But what Dr. Mooney’s lab was able to do was actually do some controlled experiments during construction of coastal infrastructure in Woods Hole, where they are located and show some of the effects of pile driving on smaller creatures, on squids and fish. So in the past, there have been quite a few studies on impacts of pile driving associated with marine mammals, but none that I could find to do with non-marine mammal ocean animals, so with fish or squids. And so they had a really nice study on longfin squid, which are a commercially important species here, and were able to show that at least in their case, in their study, there was no indication of hearing loss in the squid associated with the pile driving. And they also looked at behavioral patterns of black sea bass, which are another commercially important and recreationally important species up here in New England. And they showed there were behavioral changes, as you might expect, from the fish in the pens that were near the pile driving, but the fish resumed their, what we'll call their regular behavior when the pile driving stopped.

So there's a number of interesting questions here that we don't have comprehensive answers to of how the effects of pile driving, would they actually have any lasting effect or is it a temporary thing that requires a mitigation, like a bubble curtain, which is already often employed for marine mammal protection?

Kat Setzer (24:22)

Let's move out of the water. How does research in terrestrial environments differ from research conducted in marine environments? And what kind of research has been done in terrestrial environments?

Edward Walsh (24:32)

So, as we've heard from the marine perspective, a great deal of climate-related acoustics research depends on passive acoustic monitoring. And the same is true in terrestrial systems. Long-term recordings are used to track not only the changes in soundscapes, but to shifts in animal vocal behavior and disruptions in phenological patterns—that is, the disruption of natural biological system cycles, for example, breeding outcomes, insect choruses, the timing of bird song, that kind of thing. 

However, it won't surprise anyone to hear me say that terrestrial and marine environments differ in important physical and practical ways. And one of the most obvious differences is related to sound propagation. Sound generally travels much farther in water than in air, mainly, of course, as we all know, because air is less dense than water, and as a consequence, sound energy is lost more rapidly in air than in water. But that isn't the entire story by any means. Sound transmission is also shaped by a slew of interacting factors that include the structure of the vegetation layer in a given environmental setting, ground conditions, wind and temperature gradients, humidity, and many, many other environmental factors, including things like atmospheric turbulence, the character of terrains and buildings, leaf litter, a whole variety of other factors. But all of this translates into a terrestrial acoustic monitoring picture that is often more local and habitat-dependent than marine monitoring. And why is this the case? Well, it's because on land, sound navigates a much more irregular propagation environment, in which each condition, each factor, can scatter sound, absorb it, reflect it, and refract it, and also mask it differently. As a consequence, microphones sample a less uniform acoustic neighborhood, if you will, than a hydrophone does. The microphone placed in a dense forest understory will almost certainly detect or hear a very different biological community than one placed along a stream corridor or on a ridge, for example.

Kat Setzer (26:44)

Right, right. So is it just that there's kind of like more of those subtle changes to the environment? Like if the leaves on the ground change a little bit, then all of a sudden everything's refracting differently than it was twenty minutes ago, you know? 

Edward Walsh (26:56)

Exactly. Yep, exactly.

Kat Setzer (26:57)

Yeah. Okay. So can you comment on why all this matters in a climate change context?

Edward Walsh (27:01)

Sure. climate change matters because, simply enough, a warming planet can modify the physical features that determine how sounds travel, something that's also being discussed, of course, in a marine context. So you think of heat-induced droughts and wildfires and pest outbreaks, and all of these things and a great many other consequences of a hot planet change both the sounds produced in a landscape and the way those sounds propagate through it. And forests are a pretty good example. As with all other terrestrial settings, the forest habitat should be thought of as an acoustic filter, a filter that determines what can be recorded at any particular place in time. For example, sound through a forest must navigate large structures like tree trunks and branches that affect, reflect, scatter, and refract sound. And dense vegetation and canopy structures tend to attenuate higher-frequency sounds, which, by the way, in a very significant context, can limit the long-range communication of many animal calls. As forest becomes hotter and drier, they obviously become more fire-prone because the properties of the filter change. A dense humid forest and a drought-stressed or fire-damaged forest will sound very different, not only because the animal community changes, but because the physical propagation environment changes as well. 

So if we kind of shift gears here a little bit and think about another terrestrial environment, the desert, deserts produce or present a very different case. Desert soundscapes are often sparse and climatically extreme, but they are not by any means simple. Their acoustic activity profile is typically concentrated into short daily or seasonal windows. You know, here think the dawn, dusk, nighttime time periods. And during those windows, insects, amphibians, birds, bats, and mammals generally become acoustically active in highly patterned ways. And in a warming world, those timing patterns destabilize. They can become shorter, shift in time, and become less predictable.

Kat Setzer (29:12)

Okay, okay. So you actually you mentioned desert animals. How do we expect climate change to affect different animal groups?

Edward Walsh (29:18)

So I think it's safe to say, even though this these differences are a little less clarified than than you might like, I think it's safe to say that amphibians are especially vulnerable to a hotter planet because they are ectothermic ,and they depend on water for reproduction and for survival, as was mentioned earlier, you know, with with regard to marine animals. But birds are also seriously vulnerable in desert systems because water is essential for evaporative cooling. 

But one of the most interesting considerations here has to do, in my opinion, with bats. Bats may be buffered from a climate change consequence somewhat by nocturnal activity. But having said that, they nonetheless remain vulnerable through reduced water availability and changes primarily due to the availability of their prey, to the availability of insects. And so some small mammals may be partially protected by nocturnal behavior and burrowing, but even here, the broader ecological network can be disrupted. So in deserts, climate change-induced acoustical disruption may be best understood in terms of temporal compression of seasonal windows, fewer, shorter, or less reliable periods when the landscape comes alive acoustically.

Kat Setzer (30:32)

Okay. So, besides forests and deserts, are there any other environments ideally suited to study climate change and sounds questions?

Edward Walsh (30:40)

Yes, there absolutely are. Mountains and alpine environments are indeed especially interesting because climate gradients are spatially compressed under these conditions. A change that might occur over hundreds of miles elsewhere can occur over a relatively short elevation gradient. That makes mountains powerful natural laboratories for studying climate-related changes in sound propagation, in animal behavior, and in vocal communication. 

Although not part of our special edition, a particularly elegant example comes from Peter Narens and Sebastian Minderink, who studied the Puerto Rican coke frog along an elevation gradient. They compared advertisement calls recorded along a tropical mountain gradient with recordings made along the same gradient more than two decades earlier. At the same elevations, call pitch had significantly increased and call durations had become significantly shorter. Those changes were consistent with climate links, shifts in body size, and elevation associated temperature effects. The thing that makes this study especially powerful in my mind is that the acoustic changes were linked to archive temperature data over the same time period. The rise in temperature served to predict the observed shifts in call structure. Pretty amazing, it seems to me. But in that sense, the frog's call became a biological indicator of climate change, linking temperature, elevation, body size, and vocal behavior in a relatively simple natural system. So we shouldn't leave this discussion without emphasizing the fact that similar issues arise in all environmental settings: grasslands, savannas, wetlands, fragmented landscapes, and ecotones (those are the transition zones between ecosystems). And climate change is not simply making terrestrial environments louder or quieter, it is retuning them. Each landscape has its own acoustic structure, its own biological community, and physical constraints on sound transmission, so each will change in its own way.

Kat Setzer (32:50)

Right. That totally makes sense. So which animal groups have been studied most often in terrestrial climate acoustics research?

Edward Walsh (32:58)

So, from the perspective of species, much terrestrial research has been focused on birds, frogs, bats, insects, and to a lesser extent, but some mammals. The strongest mechanistic data are probably derived from ectotherms, especially from frogs and insects, because their vocal behavior and sound production physiologies are highly temperature-dependent. Temperature changes affect call rates, pulse rates, call durations, and other related features. That said, I think of bird study outcomes having contributed fundamentally to our understanding of climate change influences on phenomena like migration patterns and breeding phenology, and as well as timing of dawn choruses and changes in species composition within a habitat. 

So a great deal less, actually, is known about terrestrial mammals. But the likely effects of climate change are broad, affecting what I would say is the standard collection of consequences, altered calling rates, altered seasonal calling window durations, altered predator-prey listening conditions, the effectiveness of long-distance communication in open habitat.

Kat Setzer (34:12)

What do you mean by mechanistic data?

Edward Walsh (34:14)

Good question. Mechanistic data are data that help explain how or why something happens rather than simply showing that it happened. It helps to identify the processes responsible for an event or a change. In a climate change context, descriptive acoustics data might explain why, what factors are responsible for a bird species to call less often, or shifting its calling time, or why higher temperatures affect breeding timing. In this sense, mechanistic data connect climate-driven environmental change to measurable outcomes and making it easier to interpret soundscape changes and predict what they may mean in an ecosystem context.

Kat Setzer (34:58)

Okay, okay. So it sounds as though marine and terrestrial environments are very different, which not totally surprising, but are there still any common principles that connect them?

Edward Walsh (35:08)

There absolutely are. Marine and terrestrial acoustic environments are clearly different, but they are closely related from a conceptual point of view. In both settings, sound is produced by a wide range of biological factors, which I should mention include human influences as well as abiotic sources, and those sounds travel through and are modified by a physical medium, of course. Likewise, animal communication is influenced by background noise, and acousticians working in both settings have to deal with the use of instruments with finite detection limits. And in addition, the execution of successful acoustic monitoring studies in both environments requires the use, obviously, of calibrated sensing systems and long-term passive recording strategies. So the environments are not equivalent, but the same fundamental acoustical framework applies to both.

Kat Setzer (36:02)

So there was also some research that related to the built environment and climate change. What sort of things are architectural acousticians looking at with regards to climate change?

Edward Walsh (36:11)

So this definitely isn't my area of expertise, but it doesn't take an expert to recognize that architectural acousticians are increasingly asking how buildings can adapt to climate change without creating new problems for its inhabitants. As the planet warms, the almost certain increase in the use of air conditioning systems and heat pumps and mechanical ventilation devices and the like will increase, and ultimately those conditions could create a problem, of course. While being essential for personal comfort and health, they will also introduce noise and vibration if they aren't properly designed. So one major concern is figuring out how to provide cooling while maintaining quiet and healthy indoor living environments.

A second major area that comes to my mind is that the materials and construction methods used to reduce carbon emissions. The materials used to construct low carbon buildings, things like lighter weight building components, can be very beneficial environmentally, but they may underperform relative to traditional heavy construction materials when it comes to blocking sound and limiting the destructive influence of vibration on building structures, infrastructure, those kind of things. The bottom line is that the architectural acousticians are working with building designers to develop building strategies in an integrated framework, rather than as separate problems. The broader goal is pretty simple, right? To make buildings that are greener but comfortably livable.

Megan Ballard (37:48)

We do have one article related to architectural acoustics in our special issue, and it was a case study on floor construction and so they really did look into some of the topics that Ed was describing in his response. So the kind of construction of the building is a huge upfront cost, and so they looked at how to put in…  it was like the floor that goes like in a multi-level building, how the floor needs to be made to isolate sound, but how that can be done in kind of an environmentally responsible way. So maintaining the noise isolation between separate floors, but still making it quiet, but also using of environmental conscious building design. So it's like an engineering design problem where environmental consciousness factors in along with the of course acoustic properties of the floor.

Kat Setzer (38:41)

Right, that makes sense. 'Cause you can't use big thick slabs of concrete anymore to just buffer the sound waves or absorb the sound.

Megan Ballard (38:49)

Right, yep. Yeah, and so the paper was presented as a case study for that, but also it could be applied to different building materials like the windows and the lights and the HVAC, as Ed mentioned.

Kat Setzer (39:01)

So we've been talking about the future of acoustics research related to climate change throughout this discussion, but do you have any other thoughts related to the future of research related to this topic?

Megan Ballard (39:10)

Well I felt like the papers and the special issue really show how much acoustics is branching out and contributing to climate science in our oceans, atmosphere, and land, and even the built environments that we just talked about. Taken together, they highlight how powerful acoustic approaches can be for tracking environmental changes and ecosystem responses over long periods, often at scales that are difficult to capture with other methods. As climate change continues to alter the way sound moves through different environments, it's clear we’ll need continued progress in acoustic sensing, modeling, and data analysis. Looking ahead, this work will be increasingly interdisciplinary, bringing together scientists and tools from different fields to better understand these complex interconnected systems.

Lauren Freeman (39:57)

So I just really wanna highlight Megan's point here about how difficult it is to monitor underwater ecosystems in particular, but some terrestrial ecosystems as well. Many underwater sites are difficult to access on the very best of days and water clarity, even in tropical water, that beautiful tropical water you think of when you go on vacation, it's still not very good. At best you're talking about maybe 200 or 300 feet or a hundred yards. So that really limits visual methods from if you think about critter cameras or things you might use on land to understand what's going on. Acoustics offers a really timely opportunity to track underwater animals and ecosystems over space and time as our planet is shifting rapidly.

Edward Walsh (40:37)

I completely agree. And I think the field is heading toward larger, longer, and more integrated monitoring systems. And passive acoustic monitoring systems will become part of a broader climate observing networks. So passive monitoring systems will sit alongside and connect with other data acquisition systems, like weather stations, satellite imaging systems, camera traps, vegetation surveys ,and even DNA surveys. I find the DNA part to be a particularly interesting because D analyses will permit climate scientists to better understand the consequences of climate change by revealing not only which species are present, but how populations are shifting and responding biologically to the changing environment. So the the goal isn't to record more sound, it will be to convert sound into reliable indicators of relevant biomarkers of change in biodiversity and phenology, as well as habitat quality and a host of other climate-induced changes, like animal movement, ecosystem disturbance, that kind of thing.

Megan Ballard (41:42)

I agree. This certainly describes the trend that Matt, Hanne Sagen, and Peter were working towards in their Arctic observing system, which is a large network of sources and receivers for continuous long term tomography measurements while also enabling sources for under ice navigation.

Kat Setzer (42:00)

Yeah, it sounds like that would require a lot of data processing capabilities, though, as well. So what has to improve for acoustic monitoring to become a reliable climate observing tool?

Edward Walsh (42:10)

Well, from my point of view, improvement in automated detection and machine learning algorithms, along with the availability of improved analytical tools, will be key, I think that's for sure. But I would also say possibly even the number one challenge will be developing generalizable models, models that will be useful regardless of what region is being monitored or seasons, habitats, recorders, or species. I think acoustics will play an especially important role because it can reveal changes that are difficult to observe visually. It was referred to earlier, I believe. At night, dense vegetation across remote landscapes or even over long time scales. So in that sense, acoustics is not just another monitoring tool, it is a way of listening to climate change as it reorganizes biological communities, human environments and the soundscapes that connect them.

Lauren Freeman (43:04)

Yeah, absolutely, Ed. We had three different papers in the special issue that we're talking about today, from three totally different organizations from the Sunway Center for Planetary Health in Malaysia, the University of New Hampshire, and Woods Hole Oceanographic Institution in the United States, each tackling the challenge of having a very vast amount of data that's associated with long-term acoustic data sets. And each of these took a unique tack of using machine learning tools, ranging from very well-trained algorithms like BirdNet to understand penguins in Antarctica, where we have increasing winds associated with climate change that are interfering with acoustic recordings. And a couple of bespoke approaches, so we had a convolutional neural network for fish calls on coral reefs and a deep neural net that, this was really clever because bioacoustics are very tightly tied with the change of light, but it was trained on key time-of-day features in the rainforest to rapidly extrapolate more information about that system.

Kat Setzer (44:05)

Right, right. Do you have any closing thoughts?

Edward Walsh (44:07)

Well, I mean I I do. I guess I would close by simply reminding everyone that the climate crisis is real. Climate scientists have demonstrated beyond any question that climate extremes are reshaping the planet's living and non-living systems. And in that framework, monitoring sound will be a crucially important measure of the state of our ecology. The climate crisis is changing what the planet sounds like, and acoustics will give us a way to detect at least some of those changes early, monitor them continuously at scales that are otherwise difficult to achieve by other methods.

Megan Ballard (44:41)

And before we wrap up, I want to encourage everyone to take a look at the articles in the special issue on climate change. We also have a related article coming up in the fall issue of Acoustics Today. These are excellent opportunities to learn more about the important work being done across our field to understand how climate change is affecting sound in acoustic environments. And while climate change may not be the focus of everyone's research, its impacts touch many areas of acoustics. By staying informed and supporting this work, we can all contribute to a deeper understanding of these challenges and their implications for our science, our communities, and our environment. And thank you very much.

Kat Setzer (45:19)

Yeah, thank you.

Lauren Freeman (45:20)

You know, I really think that my colleagues said it best here, but it's been such a pleasure to work on this special issue with Megan and Ed and with Dan and YT, and to see research from across the ASA community on how sounds that we're recording are reflecting the health of the planet. So we really hope that you enjoy reading the articles in the special issue.

Kat Setzer (45:42)

Well thank you all for taking the time to speak with me today. It's really fascinating how so many of the subfields of acoustics have been impacted by climate change. Even though the special issue is closed, I imagine it will be a hot topic in the acoustics community for quite some time. Thank you all for putting the work into this special issue together and have a great day.