Ariel Conn: Hi everyone, Ariel Conn here with Not Cool, a climate podcast. Today, we’ll be looking at some of the other sources of climate change. We hear a lot about carbon in the atmosphere, and for good reason: CO2 accounts for about half of global warming. But what about the other half? Today we’re joined by Ilissa Ocko, who will walk us through the other greenhouse gases and aerosols that are impacting the global climate. 

Ilissa is a Sr. Climate Scientist at the Environmental Defense Fund, where she pursues climate science research and provides scientific guidance for climate change communication and policy. Her research focuses on the long- and short-term climate impacts of several greenhouse gases and aerosols. She is committed to communicating science to non-experts using plain language and powerful visuals, and she recently represented the U.S. in an international science communications contest.

Ilissa, thank you so much for joining the show today.

Ilissa Ocko: Thanks so much for having me.

Ariel Conn: So before we get into a lot of the work that you've been doing, I actually want to step back and ask a pretty basic question: what are aerosols? What are these things that are in the air that we're breathing?

Ilissa Ocko: So there are millions and millions of gases and aerosols all around us. Aerosols are solid or liquid particles that are in the atmosphere, as opposed to a gas. And a lot of them are just naturally in the atmosphere. For example, when we have a dust storm over a desert, it kicks up some of the sand, and a portion of that can remain in the atmosphere. We can breathe that in; it can stay there. And that's natural, for example. But there's also a lot of human activities that are introducing even more of these aerosols into the atmosphere than otherwise would be there.

Ariel Conn: And can you give some examples of what anthropogenic aerosols would be?

Ilissa Ocko: Anthropogenic aerosols are the same type of aerosols that are naturally there, they just have anthropogenic sources. And when we say anthropogenic sources, we mean human activities that are also emitting them into the atmosphere. So for example, when we burn coal, it also introduces sulphur dioxide into the atmosphere, which is a gas — but then it quickly becomes sulfate, which is an aerosol. But sulfate is already in the atmosphere, for example from biological activity in the ocean that also emits sulphur dioxide into the atmosphere, which turns into sulfate. So the sulfate is in the atmosphere from both natural and human sources.

Ariel Conn: And so any issues that we'd have, it would be that there's just more of these aerosols, not necessarily the type?

Ilissa Ocko: Yes, exactly. Sea salt for example is a natural aerosol that is in the atmosphere because it gets kicked up from ocean waves. But for example, sulfate and black carbon and organic carbon: those are all aerosols that are naturally in the atmosphere, but we also add to them in the atmosphere. So it's a matter of us changing the composition of the atmosphere.

Ariel Conn: You were part of a report that came out in 2011, where you talk about things that policymakers can do to address non-CO2 climate forcers. What are climate forcers?

Ilissa Ocko: A climate forcer is any pollutant that we emit that can perturb Earth's energy balance. So we have sunlight that comes into the earth, that warms up the earth, and then the earth emits some of this excess as heat. And then these constituents in the atmosphere can interact with either sunlight or heat or both. And so we call a climate forcer anything that can really change Earth's energy balance. Carbon dioxide can trap heat in the Earth's system, and so it is thus forcing the climate by changing the energy balance.

Ariel Conn: So your report was looking at the non-CO2 climate forcers. What are some examples of these non-CO2 climate foresters? You sort of got into it a little bit.

Ilissa Ocko: So, we focus so much on carbon dioxide because we emit so much of it into the atmosphere, and because it lasts for a really long time — and so it commits our planet to warming for centuries. But there are a number of other climate pollutants, or climate forcers, that we also emit that play a major role in changing Earth's climate. So if we look at CO2's contribution to today's warming, it actually only accounts for half of the warming that we are experiencing. The other half of the warming is coming from what we consider non-CO2 climate forcers. We have other greenhouse gases that trap heat: for example, methane and nitrous oxide. And we also have these aerosols — which are not gases, because they're solids or liquids — that are in the atmosphere, but they also change Earth's energy balance and contribute to the climate change we're experiencing today.

Ariel Conn: And you brought up black carbon earlier. Can you explain what black carbon is and what role that plays?

Ilissa Ocko: Black carbon is essentially elemental carbon. When you see big trucks drive by and you see this puff of black smoke that comes out of the engines, that black smoke is predominantly black carbon. It's a solid particle; when we breathe it in, it can affect our lungs; it's a major air pollutant. But it also is very effective at trapping energy. It can trap a million times more energy than carbon dioxide can, pound for pound. So it is an incredibly powerful climate forcer — we just emit a lot less of it than carbon dioxide, so it doesn't contribute as much to warming today as carbon dioxide does. But it still contributes around 15% to the warming that we're experiencing today.

Ariel Conn: So when we look at the non-CO2 climate forcers combined, how much are they influencing the warming that we're experiencing, compared to carbon?

Ilissa Ocko: Around half of the warming that we're experiencing today. 

Ariel Conn: Wow.

Ilissa Ocko: So this is why we need to focus on not just carbon dioxide but also these non-CO2 climate forcers, because they make up a considerable fraction of today's warming. But they're also more complicated than that; some of these non-CO2 climate forcers cool the earth. So it ends up being this balance between the warming pollutants and the cooling pollutants that dictates how our temperatures actually will change.

Ariel Conn: In terms of us emitting the non-CO2 climate forcers, are the processes basically the same for carbon? Are they part of most of the processes that are also releasing CO2? Or are there things that we're doing that are releasing, say, more black carbon or more methane or some of the others that you mentioned?

Ilissa Ocko: There definitely is some overlap between the sources of a lot of these climate pollutants. For example, coal plants are a major source of CO2 but also a major source of the sulfate aerosol in the atmosphere. But there are also some really distinct sources that are separate for the non-CO2 climate forcers. For example, around over a third of methane is emitted from agriculture. A lot of this is coming from livestock, but rice production also contributes. So for example, these are activities that don't necessarily contribute a lot to CO2 emission but contribute a lot of methane emissions.

Ariel Conn: We hear about fossil fuels a lot with CO2. Are those also a source of these other non-CO2 climate foresters?

Ilissa Ocko: Fossil fuels definitely contribute to the emissions of these other non-CO2 forcers to varying degrees. For example, the oil and gas industry is responsible for around a quarter of the methane we emit into the atmosphere. There's also a certain fraction of black carbon that comes from vehicles that burn diesel. And so we see around 20% of black carbon coming from diesel trucks. We also see around 10% of black carbon coming from coal-fired power plants. So there definitely are some overlap with the sources, and if we were to address fossil fuel emissions, we would also reduce emissions of these other non-CO2 climate forcers.

Ariel Conn: And so now let's go back to methane. It's probably the one that I personally hear the most about, after carbon. Why are we worried about methane? What's the issue with that one?

Ilissa Ocko: So methane, like you said, is one of the main contributors to climate change. If we look at it in terms of which pollutants we emit and how they contribute to today's warming, it is the second largest contributor. It accounts for at least a quarter of the warming that we're experiencing today. And this is from both directly as methane, the greenhouse gas, but also because when methane breaks down it turns into tropospheric ozone, which is another strong absorber of heat. And so methane overall is around 100 times more powerful at trapping heat than carbon dioxide. So that's one of the main reasons we care about it.

Another reason we care about it is because we're admitting a lot of it into the atmosphere, and if we don't take actions to curb our emissions, we will see a lot more warming in the future — even if we work really hard to decarbonize society and wean ourselves off of fossil fuels — because methane has some distinct sources, such as agriculture.

And if we look at annual emissions of methane from human activities and we look at how those will affect warming of the planet over the next 10 years, we'll actually have 30% more warming coming from the annual methane emissions than we will from annual CO2 emissions from fossil fuels. The main difference between methane and carbon dioxide is that it doesn't last as long in the atmosphere. So it doesn't build up over time and commit our planet to warming for centuries in the way that CO2 does.

Ariel Conn: So I'd like to follow up with that, because that's one of the reasons that I've heard for not being as concerned about methane is that it won't last as long. But you also just said that it breaks down into ozone, which can still absorb energy?

Ilissa Ocko: Yes. Tropospheric ozone is another strong greenhouse gas.

Ariel Conn: So how long does that last?

Ilissa Ocko: That actually only lasts for at most a couple of months.

Ariel Conn: Okay.

Ilissa Ocko: So the tropospheric ozone doesn't last very long itself. Methane also breaks down into stratospheric water vapor, which also has a warming effect on the earth, but that again does not last very long. A small fraction of methane is eventually oxidized into CO2, which does last for a long time, but because the amount of methane that we omit is so much less than CO2 — around 100 times less — that is not a main contributor to long-term climate change.

But I want to mention two main things about why we care about methane and why it is essential that we reduce emissions now. The first is that even though methane will only last in the atmosphere for about a decade — and so it will be removed fairly efficiently — the warming that it causes in that short term can be absorbed by the oceans.

We know around 90% of the excess heat that have been trapped from human emissions of greenhouse gases has gone into the oceans. And so then that warming that came from methane in the atmosphere — even though methane was only there for let's say, 10 years — is now in the ocean where it can last a lot longer and contribute to sea-level rise, for example, over the long-term. So even though methane is a short-lived climate pollutant, it doesn't have short-lived impacts.

Ilissa Ocko: The second thing I want to mention is that because methane doesn't last very long, if we reduce emissions, we can have a near immediate benefit to the climate. Methane accounts for at least a quarter of today's warming, and if we were to reduce all of our emissions of methane, we would see about a quarter of today's warming disappear over the next 10, 20 years, which is an incredibly powerful opportunity that we don't have with CO2, for example.

Ariel Conn: So given that, as you said, methane is associated with agriculture and food production, how do we decrease methane emissions?

Ilissa Ocko: So we can reduce methane emissions from either production of our food: for example, we can improve manure management practices, we can provide feed supplements for cows to digest when they eat their normal food that can inhibit some of the production of methane in the cow's gut. We can also improve some of our rice practices: for example, there's different irrigation methodologies that can reduce emissions. And so there are a number of strategies that we already have available to reduce methane from the production side of things. But then we also could modify some of our dietary behaviors in the future, which is more of the social change, which obviously also would play a role in reducing emissions.

Ariel Conn: And so with regards to the methane being released from agriculture, is that still — as with carbon dioxide — connected to newer technologies and methods that we're applying to agriculture? Or is this more an issue of growing populations eating more meat or something?

Ilissa Ocko: Yes, a huge portion of the methane that is being emitted from livestock and rice, for example, is just our increased demand for food as the population grows. But there are technological considerations as well. Around 10% of the greenhouse gas emissions coming from agriculture are associated with energy use. So we expect that as we trend toward renewables, for example, we can reduce a certain amount of emissions from the agriculture sector just by improved energy technologies. But a lot of these emissions are just coming from the livestock and how their biological processes function. So as long as we keep having livestock around, they will keep emitting methane into the atmosphere.

Ariel Conn: Okay. And so you wrote a paper called Rapid and Reliable Assessment of Methane Impacts on Climate. And one of the things that it seemed to me, looking at that, is that it's harder to model methane than it is carbon. Is that correct?

Ilissa Ocko: It's not necessarily harder to model methane compared to carbon dioxide. One could actually say it's easier, because it has a fairly simple decay reaction in the atmosphere compared to carbon dioxide, which can have several different fates. Carbon dioxide can be taken up by plants; it can be taken up by the oceans; it also can just remain in the atmosphere completely untouched and lasts for thousands of years. So in that sense, methane can be simpler. The problem is that we focus so much on CO2 that we always look at how methane impacts the climate as a comparison to CO2. And that has led to some really simplified climate metrics that don't do a good job explaining how methane impacts the climate over different timescales.

The problem we end up having is that we have these really sophisticated climate models that are incredibly impressive but take a really long time to run these simulations and require special infrastructure. And then you have these more simplified metrics that don't do a good job elucidating these temporal trade-offs. And so what else can you use for understanding how methane impacts the climate? And what you can use are reduced complexity climate models, but they're not necessarily calibrated or tested for how well they model methane just because we focus more on CO2. And so this paper was really just making sure that some of these simpler models are able to adequately portray how methane impacts the climate.

Ariel Conn: I want to follow up with this idea of the timescales. That's another paper that you wrote that I thought was really interesting, was the comparison between looking at the impacts of greenhouse gases on 20-year timescales versus 100-year timescales. What does that mean to look at a 20-year timescale versus a 100-year? What types of projections are we making?

Ilissa Ocko: So we care about climate change over all timescales. That is very clear. We care about what's happening today; we care about what happens during our lifetimes. But we also care about what happens for future generations — for our children, for our children's children. And different climate pollutants affect the climate over different timescales. So we keep talking about carbon dioxide, how it builds up in the atmosphere, it stays there for a really long time. That climate pollutant strongly dictates what these long-term climate changes look like: how high the sea-level will get; how much warming will we ultimately have? Will any of our biomes shift? For example, will the Amazon turn into a grassland? All of those are really long-term issues that we care a lot about and that ultimately rely on how much carbon dioxide is emitted.

But then we have these short-lived climate pollutants, like methane, that are much more powerful at warming the climate in the near term, and therefore they end up dictating how fast the climate is warming. And that impacts the climate changes that we're seeing today — for example, how fast the sea-level is rising right now; how much extreme weather events are occurring and how they're intensifying; when we will reach certain tipping points, how fast will those happen? There's all sorts of climate changes that are happening right now that we could mitigate if we reduce these short lived climate pollutants.

So overall, we care about climate change over all timescales. And basically when climate impacts are reported, it's usually in this 100-year time horizon, it's over the long term. And what we're trying to say in this paper is that, well, the near term matters too. The 20-year time horizon matters too. So what you really need to do is look at both of these timescales. Whenever you report climate impacts, don't just do 100-year, don't just do 20-year, but do both. This is the way to give us the best understanding of what's actually happening in the climate and how our activities are affecting climate change in both the near and the long term.

Ariel Conn: Why haven't we been doing that?

Ilissa Ocko: There are always trade-offs that are going to need to be addressed, and ultimately it becomes a value judgment of, well, we have this tough decision to make; what do we care more about? But when we're talking about using both time horizons, we're just trying to provide the decision maker with the best available information. And then whatever they choose to do with that information is up to them and this ethical value judgment. But from a science perspective, if we're not supplying the decision maker with all the information, then how could they make the best decision without even knowing how their decisions could impact climate over different timescales?

So one of the analogies that we often use is that it's similar to your blood pressure measurements. You're never just given one number; you're given two numbers, something over something else. And if you were just given one number, you would think, "Wait, what about the other one? What am I missing? This is only part of the story." And that's what this is. We've been providing only part of the story for decades. And you ask, well, how this even happened? Well, it just evolved over time, as policy makers trying to understand how different emissions impact the climate just essentially and arbitrarily chose 100 years because they were provided three options in a report in 1990: 20 years, 100 years, and 500 years. And it seemed like 100 years was the middle of the road, so let's just do that, and then it just kind of spread. And now this whole community just uses 100 years, when really there is no scientific basis for it other than it just evolved that way. So we're trying to change that standard, such that people report both time horizons: 20 and 100 years.

Ariel Conn: So when we hear reports that say, "X is going to happen in the next 100 years," and the response is, "Well, that won't affect me. Maybe my grandchildren or something like that," is that sort of an incomplete narrative — that there is stuff that's going to be happening in the next 10, 20 years that we just haven't been well-informed about?

Ilissa Ocko: Somewhat, yes. It is a very complicated issue because basically what we're doing is we're looking at, for example, how driving your car will impact climate over the next 100 years. And that's just built into the metric, but a lot of people drop out the 100 years and just say, "Here's how a car will affect climate compared to, for example, eating a hamburger." And because those activities emit different climate pollutants that impact warming over different timescales, that's why these metrics have to have a time horizon in order to compare the impacts to one another.

So what we end up doing by framing everything in this 100-year timescale, is that we're masking any of the near-term impacts. They're still part of the calculation, but they're spread out over 100 years. So for example: you eat a hamburger that has a carbon footprint to it. The emissions from that hamburger will impact the climate mainly over the next 20 years. But what we're doing is we're spreading out those emissions over the next 100 years instead of just looking at over the next 20 years. So it ends up just being misleading, and downplays the role of eating a hamburger compared to driving your car.

Ariel Conn: And then, so to make sure I'm understanding this, this is where that trade-off would come in: with the hamburger, you're going to have a much higher impact over the next 20 years, but with the car, it's going to be a higher impact over the next hundred — and so trying to find that balance?

Ilissa Ocko: Exactly. And so that's a challenge, and it will be inherent to a lot of decisions. But from a science perspective, we just want to provide all of the information so that we're aware of these tradeoffs when we make a decision. The way it is right now, we're not even aware of the trade-offs that we may or may not be making.

Ariel Conn: And so this paper came out in 2017. Are you seeing policymakers and scientists considering these two different timescales more? Or is this still a problem that needs to be addressed?

Ilissa Ocko: We are definitely seeing industries that are starting to adopt this approach, which is exciting. We're definitely still working on governments adopting this. It's a very complicated process because it basically depends on certain government organizations that set the precedent for everyone else. And then once those organizations — for example, the IPCC: the Intergovernmental Panel on Climate Change — if they were to recommend this approach, then you would see this approach being adopted by national and city governments worldwide. But a lot of those governments will look to those larger international organizations for guidance. And unless that's happening, they won't change their practices. 

So we are trying to work with the different entities to get them to adopt this still relatively easy approach, but one that provides a lot more information than they're getting and giving right now.

Ariel Conn: Does it seem like you're getting a good response to that?

Ilissa Ocko: It really depends. A lot of the push back we do get is that, “Well, as long as the IPCC tells us to use GWP 100” — which is global warming potential over a 100-year timeframe — “we want to be consistent with them and so we will do what they tell us to.” And the IPCC only comes out with new reports every five to seven years. So it ends up being this long process of getting to that point where we can shift the community towards that approach.

So I think that the main pushback ends up being, “Well, we want to use what's consistent with everyone else, and if other people aren't doing this then we don't want to do it.” But we saw that, for example, with the hydropower industry, that were resistant to using this approach; but then the lifecycle community apparently started using this approach, and then all of a sudden the hydro-power community was on board and happy to adopt this. So it seems like an issue of, “If everyone's doing it then I'll do it too.” And it's just getting to that point where enough people are doing it that everyone else follows suit.

Ariel Conn: I want to come back to a comment you made earlier where we were talking about the climate forcers, and you mentioned that some increase warming and some can actually increase cooling. And I'm curious about which ones can increase cooling, and to what extent that can help balance things out — what warms and what cools?

Ilissa Ocko: We have the greenhouse gases, which all trap heat; but then the aerosols are a lot more complicated than the greenhouse gases. They come in all different forms, shapes, sizes. And primarily because they're bigger than greenhouse gases in terms of their size, they actually interact with sunlight rather than heat. And it depends really on the composition of the aerosol, but some of these aerosols are really good at absorbing sunlight, and therefore they end up trapping energy in the climate system and warm the Earth. And then some of these aerosols are more effective at scattering sunlight; and by scattering sunlight they reflect some of the sunlight back out to space, and so they in turn cool the earth.

The major cooling aerosol is sulfate — which comes from sulphur dioxide emissions, which have a number of both natural and human sources. Another cooling aerosol is sea salt and dust, which have a lot of natural sources. Also nitrate, which can be emitted also from agricultural activities, and I think it's emitted as ammonia and then becomes nitrate in the atmosphere; and that also scatters some sunlight. And then organic carbon. Organic carbon is sort of the other side of the coin to black carbon. They're always co-emitted, but depending on the fuel that's being burned, they have different ratios of black to organic carbon. And black carbon is strongly absorbing of sunlight, and organic carbon is more reflective of sunlight. And so it ends up being that balance between the two that will determine how much warming we ultimately get from black carbon, because some of it is being offset by organic carbon.

Ariel Conn: And do you think we can use these types of aerosols to counter the warming? Or are you worried about risks associated with that?

Ilissa Ocko: We can use them, but it's a terrible idea. And I do not think that we should pursue those types of geoengineering activities. And one of the main reasons why is because of the unintended consequences that may happen. Sulphur dioxide emissions were a main contributor to acid rain. And it wasn't until we started reducing emissions of sulphur dioxide from coal plants in the US and in Europe that we started to see our acid rain problem, in I think the 1990s, playing much less of a role in impacting the environment.

These aerosols have other impacts other than just affecting the climate, but they also could completely change rainfall patterns. By changing the energy balance in the atmosphere, it affects the hydrological cycle. So then you can start having more rain in one area and less rain in another area. And so there's all these cascading effects that can happen, and there's no way that we can really predict all of them because we have one Earth and we can't experiment with it. So even though yes, we can counteract some of the warming with cooling from these cooling pollutants, it's not a good idea.

Ariel Conn: Okay. So what are some of the things that you would like to see society and policy makers doing to address climate change more broadly, but especially the non-CO2 climate forcers that we've been talking about?

Ilissa Ocko: We have so many already available opportunities to reduce methane emissions that we are not taking advantage of. Something that I would really like to see, that is technically feasible, is to pursue all of these methane mitigation measures that already exist — pursue them in parallel — and we can make a real dent in our warming over the next half century and full century. And so I think that's something that we're not taking advantage of now to the extent that we could be.

One of the main sources of methane emissions into the atmosphere comes from the oil and gas industry. And we have a lot of technologies available to detect natural gas leaks, to plug these leaks, to reduce methane emissions from the supply chain in a number of different ways. And so we could take initiative to enact these strategies that already exist and curb our methane emissions. We also have methane mitigation measures from livestock, and from rice, and from coal mining, and from landfills and wastewater. We have a lot of different technologies already at our fingertips. For example, we could capture some of the methane before it is emitted into the atmosphere from landfills. We could provide cow feed supplements. We could change our irrigation systems for rice production. So there are a lot of strategies that are already out there; they're just not being deployed to the extent warranted.

Ariel Conn: Is it a matter of cost, or awareness that these solutions exist, or something else that's holding us back?

Ilissa Ocko: So if you add up all of these different strategies that we could pursue, it amounts to around half of methane emissions that we could avoid and we could reduce. Around a quarter of all the methane emissions could be reduced at near-zero costs. So there's a lot that can be done with no extra costs and is absolutely cost-effective. So in that sense, cost isn't the main limitation. There is for the other methane emissions that we could reduce with available technology — cost is definitely a factor and so it does play a role. But there's also just a lot of complexities involved with distributing some of these technologies to the places where they need to be, getting the right testing to be done for them to be commercially available, working with different industries and farmers to pursue them. It would be a whole collective effort that certainly would take a lot of work, but it's definitely not impossible.

Ariel Conn: And are you seeing some of these being implemented then?

Ilissa Ocko: Yes. We are slowly starting to see some of these strategies be implemented. For example, for the feed supplements for cows: they're working their way up through the chain of getting the approvals that they need in order to be deployed more globally. We're definitely seeing the oil and gas industry commit to reducing emissions. Some of the largest oil and gas companies in the world last year made major commitments to reduce upstream emissions of methane from their activities. And so we are absolutely seeing some of the changes that we need to take place starting to happen, but they're not happening at the pace that we really need them to in order to make an appreciable impact on reducing warming.

Ariel Conn: So my last question is, are you hopeful that we will be able to make enough of a difference in time?

Ilissa Ocko: I'm extremely hopeful. Part of that is being from the generation of knowing that climate change was mainly caused by humans, knowing that we need to do something about this. I absolutely have more of a positive outlook on things. Some of that comes from the fact that I surround myself with a community that is so focused on solutions that every day I'm hearing about small wins, and these small wins really add up. And so we're seeing so much energy and activity from local governments, to city governments, to state governments. We're seeing organizations all over the world taking actions. We're seeing industries make commitments. And I'm also a big believer in technology, and I am very hopeful that we will find ways to reduce carbon dioxide emissions and other non-CO2 climate pollutants, but also even scaling up ways to remove carbon dioxide from the atmosphere, to capture carbon dioxide before it's released into the atmosphere — I'm very hopeful that we will be able to scale up and fully deploy those technologies.

Ariel Conn: Excellent. Is there anything else that you think is important to cover that we didn't get into?

Ilissa Ocko: I don't think so. I think we covered a lot. I mean, there's so much that we could cover but we’ve got to draw the line somewhere.

Ariel Conn: Yeah, it's a huge topic.

Ilissa Ocko: Yeah, no, I mean these were great questions. And some of it is just really complicated, which is why it's hard to even explain some of the nuances. And there's a reason why people can get so confused, because the science can be extremely complicated.

Ariel Conn: All right. Well, thank you so much.

Ilissa Ocko: Thanks for having me.

Ariel Conn: You’ve likely heard a lot about the burning of the Amazon rainforest this year. Well for the next episode, we’ll be joined by Deborah Lawrence, a professor of environmental science at the University of Virginia, who will explain not only why the Amazon is so important to our climate, but the role that all forests have in regulating climate change.

Deborah Lawrence: I think some of the most interesting work has been to look at what happens with the progressive deforestation of the Amazon. What you see is that across different models with different modeling groups, it looks like there is some kind of tipping point at which you go from a system that is stressed but still a rainforest to a system where suddenly it's really much hotter and drier. And so even though you haven't deforested the rest of the Amazon, you end up with a different kind of forest, because it's stressed out.

Ariel Conn: And as always, if you’ve enjoyed this show, please take a moment to like it, share it, and maybe leave a good review. I hope you’ll join us for the next episode.