In this week’s episode, host Daniel Raimi talks with Emory University Professor Noah Scovronick, who recently coauthored a study in the journal Nature Climate Change that assesses the impacts of climate change on heat-related human mortality over the past three decades. While widespread evidence of impacts due to climate change exists across the globe, Scovronick finds that some areas, such as southern Europe, have experienced especially high burdens as temperatures have increased. Looking forward, Scovronick notes that lower-income regions of the world likely will experience more catastrophic impacts from climate change, and policymakers hoping to help people adapt to the heat can take these disparities into account.
Listen to the Podcast
- Impact of heat on human health: “Scientific evidence shows us that health impacts occur not only at extreme temperatures, like during a heat wave, but also at relatively moderate temperatures that we experience on a much more regular basis. What that means is that the increase in health problems that we see is not only from heat stroke or other forms of heat stress that we might normally think about, but also from many other types of diseases.” (4:13)
- Climate change is already deadly: “We found that about a third of all heat deaths over our study period [1991–2018] were attributable to climate change. That equates to nearly 10,000 deaths each year in our study locations. That means many cities have dozens, or even hundreds, of heat deaths each year that are already linked to climate change.” (13:32)
- Adverse impacts of climate change on lower-income regions: “There’s some evidence that those areas—places that are predicted to suffer net increases in temperature-related mortality under different climate change scenarios—will be disproportionately in warmer and poorer regions of the world. That is obviously a huge concern and something we need to really look into when we start thinking about adaptation.” (20:48)
Top of the Stack
- “The burden of heat-related mortality attributable to recent human-induced climate change” by A. M. Vicedo-Cabrera, N. Scovronick, F. Sera, D. Royé, R. Schneider, A. Tobias, C. Astrom, Y. Guo, Y. Honda, D. M. Hondula, R. Abrutzky, S. Tong, M. de Sousa Zanotti Stagliorio Coelho, P. H. Nascimento Saldiva, E. Lavigne, P. Matus Correa, N. Valdes Ortega, H. Kan, S. Osorio, J. Kyselý, A. Urban, H. Orru, E. Indermitte, J. J. K. Jaakkola, N. Ryti, M. Pascal, A. Schneider, K. Katsouyanni, E. Samoli, F. Mayvaneh, A. Entezari, P. Goodman, A. Zeka, P. Michelozzi, F. de’Donato, M. Hashizume, B. Alahmad, M. Hurtado Diaz, C. De La Cruz Valencia, A. Overcenco, D. Houthuijs, C. Ameling, S. Rao, F. Di Ruscio, G. Carrasco-Escobar, X. Seposo, S. Silva, J. Madureira, I. H. Holobaca, S. Fratianni, F. Acquaotta, H. Kim, W. Lee, C. Iniguez, B. Forsberg, M. S. Ragettli, Y. L. L. Guo, B. Y. Chen, S. Li, B. Armstrong, A. Aleman, A. Zanobetti, J. Schwartz, T. N. Dang, D. V. Dung, N. Gillett, A. Haines, M. Mengel, V. Huber & A. Gasparrini
- Floodlines podcast
- “Traces of Texas” on Twitter
The Full Transcript
Daniel Raimi: Hello, and welcome to Resources Radio, a weekly podcast from Resources for the Future. I'm your host, Daniel Raimi. Today we talk with Noah Scovronick, assistant professor at the Rollins School of Public Health at Emory University. Noah is a coauthor on a recent paper that estimates the effects of climate change on heat-related human mortality over the last 30 years. The paper covers dozens of countries and assesses how increased, moderate, and extreme heat has affected people's health on every populated continent. We'll also talk about the ways in which people can adapt to these risks and how the potential health benefits of fewer cold days compare to increased risks for more hot days. Stay with us.
All right, Noah Scovronick from Emory University. Thank you so much for joining us today on Resources Radio.
Noah Scovronick: It's great to be here. Thanks for having me.
Daniel Raimi: We're going to talk today about a recent paper that you worked on with a variety of colleagues on the health and heat-related impacts of climate change on human health. But before we get into that paper and your really fascinating analysis, can you just tell us how you got interested in working on these issues in the first place?
Noah Scovronick: Yeah, of course. To be honest, I can't actually remember a time before I was a little bit obsessed with nature and wildlife in particular. I became a father earlier this year, so naturally I went digging around in my parents' basement to find the old children's books that I’ve kept for all these years. And just about all of them were animal stories of one sort or another, often taking place in a jungle or the great plains or the Serengeti or somewhere like that. That feeling hasn't really gone away. What I think I can do is pinpoint when I made the transition from wanting a career as an ecologist to one focusing on the human dimensions of environmental issues. My first job out of college was as a research assistant studying primate locomotion in the Ecuadorian Amazon. I showed up there fully thinking I was going to be the next Jane Goodall.
I was tasked with sitting on top of a canopy platform to wait for various species of monkeys to just wander by at the perfect height at the perfect angle so I could film their movement. As you can imagine, that didn't happen very often. In fact, I don't even think I managed a single usable frame of video. But day after day, I would sit up there alone waiting. After a month or two, on the sixth or seventh hour of a viciously hot day with sweat beads crawling up my nose and in my eyes, I had this epiphany that I might be a little better suited to something that involved people, or included some occasional social interaction. That's sort of where environmental health came into the picture so here I am.
Daniel Raimi: That's a great story. That's so funny. And congratulations on becoming a dad. That's really fantastic.
Noah Scovronick: Thank you very much. He'll be a year old next month.
Daniel Raimi: Great, my little dude will turn three in about two months. I'm not too far ahead of you and I hope you're getting some sleep. So let's get into this recent paper. So as our audience knows very well, climate change and air pollution and other impacts of energy development and greenhouse gas emissions can affect human health in lots of different ways. Today, we're going to talk about this paper I've mentioned, which is called “The Burden of Heat-Related Mortality Attributable to Recent Human-Induced Climate Change,” and we'll have a link to it in the show notes, of course. Before we get into the analysis itself and some of the key results, can you just help those of us who don't remember anything from biology or human health classes? What's the physiology of heat in terms of how it affects humans and how it can increase health risks for people?
Noah Scovronick: Yeah, that's a great question. Before I answer, let me just give some relevant background information that I think will be helpful as I go into the particulars. Scientific evidence shows us that health impacts occur not only at extreme temperatures, like during a heat wave, which we hear a lot about, but also at relatively moderate temperatures that we experience on a much more regular basis. What that means is that the increase in health problems that we see is not only from heat stroke or other forms of heat stress that we might normally think about, but also from many other types of diseases. In our studies, we see links with cardiovascular disease and respiratory disease and kidney disease, and even with mental health outcomes.
That tells us that there probably is not a single physiological pathway that's responsible for the heat-health relationships as a whole, but that, instead, heat acts on the body in a variety of ways—some that are more direct, and some that are much more subtle. For example, heat exposure may influence dehydration and dehydration-related diseases, which is something we would expect. But it could also act on the body through pathways like changes in heart rate, or constriction, or dilation of blood vessels, or even where blood is concentrated in the body. In addition, heat effects may manifest differently in different people. For instance, it may affect a little baby differently than a middle-aged adult, or an elderly person, or a person with an underlying illness.
Daniel Raimi: That's really helpful. As we talk about the way that climate change has affected heat, and in turn, people's health, one thing that is always really interesting to me is how people have adapted to the places where they live, which have very different temperatures. Obviously people live all over the world, some in really hot places and some in really cold places. Can you give us a general sense of how people have adapted over time, particularly to heat?
Noah Scovronick: Sure. Once you stop to think about it, you realize that people adapt to outdoor temperatures in a huge variety of ways. Sometimes it's behavioral, like the time of day when people work outside or decide to play basketball or go for a run, or even the type of clothing we wear or the color of that clothing. That's one way that people adapt on the behavioral level. But there are also several other forms of adaptation. Another example is related to our built environment, such as what building materials we use. You may have had the experience of walking into a traditional stone farmhouse and being surprised that even on a super hot day, it can be cool and refreshing inside—actually even cooler and more refreshing than even in some of the more modern buildings.
We see evidence of this sort of adaptation in our studies. For example, in many places where the climate is warmer, a 90 degree day may not be a big deal in terms of health problems. But in a colder climate, the impact of a 90 degree day can sometimes be quite severe. There's also the issue of using air conditioning, which a number of studies have shown to be very effective at reducing heat related mortality and morbidity. Unfortunately air conditioning is not a reality for everyone, since air conditioners and the power needed to run them may not be affordable. Those are some of the adaptation strategies we think about when we're doing studies on the impacts of heat. They are not necessarily planned in any sort of coordinated way but there are opportunities to do that.
For example, we could enact specific and targeted policies to minimize heat impacts, which could be done through heat wave warning systems, public health messaging, or infrastructure improvements. Those types of interventions also have the ability to make an impact, especially as we learn more and more about how to design those policies in a way that's as effective and widely accessible as possible. That's an active area of research in environmental health right now, particularly among people who are interested in climate change.
In terms of actual physiological adaptation to heat, that's much more of an open question and something that needs more investigation. It’s something I hope to see more research about in the coming years, because that may also prove to be this conversation.
Daniel Raimi: Yeah, that's really interesting. I mean, we know that athletes can physiologically adapt to run at certain altitudes or cope with certain weather conditions. But it sounds like you're saying it's still an open question as to whether the general population might be able to adapt in a similar way.
Noah Scovronick: Yeah, exactly. We're still trying to figure out how to design studies like that for the general population. There are also questions about how long that adaptation lasts, and to what extent it really exists in terms of the range of temperatures where it may actually play a role, and whether it is possible to move beyond that in some way that we may be worried about.
Daniel Raimi: So we're going to talk about the results of your study in just one moment, but first I think it would be useful for folks to know a little bit about the methods you use to estimate how climate change has affected people's health in terms of heat-related impacts. Can you give us a sense of how you estimated these effects and also let us know what geographies you covered?
Noah Scovronick: Absolutely. Let me take the second part of that question first. This study used data from over 700 locations in 43 countries. By location here, I mean a city, or a district, or some other relatively small area within one of those countries. Those 43 countries were spread across every continent except of course Antarctica. In that sense, we had truly exceptional geographic coverage compared to other studies like this. But of course there are still big parts of the world where we didn't have the data we needed, such as India and most of Africa. To estimate the impact that climate change has had on heat-related mortality in those locations, we used a method that's actually conceptually quite simple.
First, we used real data from each location to estimate the relationship between heat and mortality. We then applied those relationships to two different sets of modeled temperature data over the study period, which was 1991–2018. One set of the model temperature data was labeled the factual scenario, and that reflects the real situations that were actually experienced by people, meaning that it accounted for our emissions of greenhouse gases, which warmed the world during the study period.
The second set of temperature estimates, on the other hand, was based on a hypothetical scenario where humans did not emit greenhouse gases or do any of the other types of climate altering activities that contributed to climate change. Then we calculated the difference in summer heat-related mortality between those two scenarios. That gave us our estimates of the mortality burden that was attributable to climate change.
That was the basic approach, but just to be clear, what it means is that relatively large climate change impacts on mortality can occur in a given location if the population of that location is either particularly sensitive to heat, or if that location experienced a particularly high level of warming during the study period. If both were true in the same location, the effects were especially bad.
Daniel Raimi: Can you maybe just elaborate a little bit on what you mean when you say a region or a location that is particularly sensitive to heat? What are the factors that lead people in a certain location to be particularly sensitive?
Noah Scovronick: Some of the factors may have to do with the adaptation strategies we've already talked about. Which of those have been implemented? It may have to do with the quality and availability of health services. It may have to do with the age of the population, or even what types of jobs people are doing—whether they're inside or outside—and that sort of thing. We've also seen that warmer regions tend to be less sensitive to sort of the same level of heat as colder regions are. But of course here, we're also talking about additional heat from human-caused climate change.
Daniel Raimi: Thank you. That's really helpful. Let's get into some of those top line results now, estimating how climate change has affected heat-related mortality over the last, almost 30 years. What are some of the top level results and how do they vary across different parts of the world?
Noah Scovronick: Across all study locations, we found that about a third of all heat deaths over our study period were attributable to climate change. That equates to nearly 10,000 deaths each year in our study locations. That means many cities have dozens, or even hundreds, of heat deaths each year that are already linked to climate change. In terms of variation in different parts of the world, while there was widespread evidence of climate impacts across our study locations, there were certain hotspots that did stand out. For example, locations in southern Europe showed particularly high burdens. There was also some indication of burdens increasing from north to south within regions, at least in the northern hemisphere where we had more data. That finding is something that could use more investigation, but it's a very intriguing result as well.
Daniel Raimi: That's really interesting. Let's talk now about some of the headline results, and I know you have results from all over the world, 43 countries, so it's difficult to summarize, but can you give us a sense of what some of the top line results were and how they might've varied in different parts of the world?
Noah Scovronick: Absolutely. We've found that across all study locations, about a third of all heat deaths over the study period were attributable to climate change. The number in the United States was similar to that one-third number, whereas some countries like Kuwait, Guatemala, and the Philippines were much higher. Other locations—for example, in China—were a bit lower. Now, a third of all heat deaths across all of our study countries equates to nearly 10,000 deaths annually, just within the locations we looked at. That means that in many of our cities, dozens, or sometimes even more than 100 heat deaths each year are already linked to climate change. In terms of variation across different parts of the world, there was widespread evidence of climate impacts across the study countries, but there were certain hotspots. For example, locations in southern Europe showed particularly high burdens. There was also some indication of burdens increasing from north to south within regions, at least in the northern hemisphere, which is a finding that's really intriguing, but could use some more investigation.
Daniel Raimi: That's interesting. When you say, increasing from north to south within a region, does that mean the northern parts of the United States, for example, would experience more acute impacts on the southern part of the United States? Or can you elaborate on that a little bit?
Noah Scovronick: That is what our results were indicating. Europe was one of the locations where we had a lot of data from a lot of different countries, and we did see fewer climate change impacts in northern Europe compared to southern Europe. But also in the United States and parts of Asia, it seemed to be showing that the burdens increased more in the southern locations than in the northern locations. That's, of course, only during the study period, from 1991 to 2018. It doesn't necessarily translate that's what we would expect to see in the future.
Daniel Raimi: And since most of our listeners are based in the United States, could you give us maybe some examples from locations in the United States that you looked at?
Noah Scovronick: Sure. I encourage you to check out the paper because we have results for dozens of cities within the United States, but just to sort of show some of the variety, we found that about eight deaths each year were attributable to climate change in Dallas, Texas. That figure was about 20 in Atlanta, where I live. In Chicago, the number was actually 90 per year. Of course, Chicago is the location of that very horrible heat wave that occurred in 1995. That was one of the events that kick-started so much of the research in climate and health, and particularly in the health effects of extreme temperatures.
Daniel Raimi: Yeah. Just sobering to kind of think about those numbers and how they translate into the real world. One thing that I'm really curious about, and I imagine our listeners are too, is this issue of adaptation, and we've talked about it already a little bit. But how do you, in this analysis, account for adaptations that might've occurred during the study period? So maybe people purchased air conditioners in 1996 in Chicago, or maybe they adapted in other ways over time in different places. How do you treat this issue of adaptation in this particular study?
Noah Scovronick: That's a really great question because you're absolutely right: there is evidence that vulnerability to heat has decreased in some places over the study. Our approach sort of implicitly accounts for adaptation, to some extent, because we use a single heat association that we estimated for each location. That can be thought of as an approximation of the average effect during the time for which we had the data. In some places it's possible that that would maybe overestimate the effect a little bit towards the beginning of the period or underestimate it a little bit towards the end of the period. However, we're fairly confident that we managed to deal with the adaptation issue to a large extent by using our method of estimating a single association over the period for which we had the data.
Daniel Raimi: One of the issues that you and your coauthors know really well is that climate change does more than just increase the number of hot days and the amount of heat. It also reduces the number of cold days, and cold-related deaths around the world account for a substantial number of deaths. This isn't something that you wrestle with in this particular paper, but I know you and your coauthors have thought about it a lot. Can you give us a sense of what the research tells us about the net effects of climate change? We know we'll have additional deaths due to heat, but we also might expect to have fewer deaths due to fewer cold days. So how do those two issues kind of balance out?
Noah Scovronick: Yeah, that's a really key point. I'm glad you asked. You're absolutely right that people die, not only from exposure to heat, but also from exposure to cold temperatures. In fact, studies have shown that in many places, the mortality burden from cold is actually quite a bit higher than it is for heat. Like with heat, deaths from cold occur from a range of causes and they increase in colder weather, both when it's very cold out and also when it's only moderately cold out. That's one of the reasons why we see large burdens attributable to cold temperatures. That leaves a really tough but important question about net effects. What our team has found in past work is that in some cities and countries, the reduction in cold deaths would in fact be greater than the increase in heat deaths. Therefore, the total amount of mortality from exposure to non-optimal temperatures may decrease under climate change. But in other places, that isn't true, and the additional heat deaths will be substantially larger than any from having fewer cold days.
So there's some evidence that those areas—places that are predicted to suffer net increases in temperature related mortality under different climate change scenarios—will be disproportionately in warmer and poorer regions of the world. That is obviously a huge concern and something we need to really look into when we start thinking about adaptation and how to reduce the impacts and protect the vulnerable populations as we move forward. It’s only going to become more important as climate change starts to become more severe over time.
Now, of course, what exactly will unfold in the future is very difficult to predict, and will depend on things we just don't know yet. One example is the total amount of warming that actually occurs and how quickly that warming happens. Also, the speed of socioeconomic development is going to be really important because that may affect some of those potential adaptation strategies that we've been discussing through this podcast. I can even think of some other variables that will affect the exact burden of temperature-related mortality as we move through time: the age structure of the population and, of course, policy investments in health services and in strategies to try to reduce impacts and protect people who are vulnerable to heat.
Daniel Raimi: It's such an interesting area of research, and there's lots of great papers that have been coming out on this topic recently. I've done a little bit of work on this topic lately too, and I'm curious to hear if you would agree with my assessment. My sense is that you see in some regions, a net increase in deaths because of climate change, and in some regions, a net decrease in deaths because of climate. But it seems to me that the effects are more severe in the places where you see the net increase in deaths. It seems to me pretty likely that the increased deaths will outweigh the decreased deaths from fewer cold days. Obviously that's not something that you can prove at this point, but that's at least my hunch from what I've read. Does that sound about right to you?
Noah Scovronick: Yeah, I think that sounds right in the sense that there will certainly be many places where those increasing heat deaths will far outweigh the reduction in cold deaths. Why that is—as I mentioned there's a range of explanations—but it will have to do with the ability, especially among people in warmer climates, to be able to adapt more than they already have. I think that's why we've seen that some of these places that are really likely to suffer are in already warm places, or in places that have less capacity to adapt. I don't necessarily think that all locations will be worse off when we sum up the reductions in cold and the increases in heat. But that's something we certainly have to worry about. Again, what's happened so far is not necessarily indicative of what's going to happen in the future, just because there's really so much uncertainty about the level of change that we're expecting and how quickly that happens. That will really affect whether we'll be able to absorb those changes, or whether they will sort of outpace our ability to start to protect ourselves.
Daniel Raimi: One other thing that comes to mind is that if you imagine a future where people adapt to higher temperatures and are no worse off than they are today, that's still a cost because they're paying money to adapt, and adaptation is costly in a variety of ways. This adaptation leading to no net change, even if that were the case, is still a costly scenario. We're investing time and resources into something that we're only having to do because of climate change.
Noah Scovronick: Yeah, absolutely. I agree entirely. Those resources are something we might be able to invest in, in other ways, to protect health or generally benefit society that we're now going to have to reallocate to adapt to increases in heat and exposure to that heat.
Daniel Raimi: One more question before we go to our Top of the Stack segment, because this is all so fascinating—I really encourage people to check out the paper to get all of the detail that's embedded in it. But as we mentioned a couple times you're part of a pretty large research group that includes dozens of collaborators from around the world that have published lots of papers on topics related to what we're talking about today. What are you and your colleagues working on now?
Noah Scovronick: Yeah, it really has been a great experience to be involved in this multi-country, multi-city collaboration, which is the largest environmental health collaboration of its kind. I believe it now stands at 73 researchers from those 43 countries. We started with the focus on the health effects of non-optimal temperature and projections of climate change impacts, the things we've been talking about today. We are still doing a lot of work in that area. So some of our current research topics include trying to focus on the relationship between age and causes of specific effects of temperature. We’re trying to get more information on who's really most vulnerable, and what's going on physiologically, and those sorts of questions. We're also doing extensions of some of those projections studies to try to quantify the benefits and costs of adaptation strategies, as we mentioned a few minutes ago.
But in addition, we've also decided to expand into many other areas of environmental health, some of which are also climate-related. For example, we're now doing quite a bit of work on the health effects of air pollution, including from wildfires, which has obviously gotten a lot of attention over the past couple of years. We're also working on the health impacts of extreme weather events.
Daniel Raimi: That's great. And yeah, it'll be so interesting to see what kind of results you and your team come up with in the months and years ahead, I'll definitely be keeping a close eye on that. And I hope our listeners will too. But let's move now Noah, to our Top of the Stack segment, where we ask you to recommend something that you've read or watched or heard that you think is really cool, and you think our listeners might enjoy. I'll start with an unusual recommendation. I'm going to recommend a Twitter account that brings me great joy. It's called Traces of Texas (@TracesofTexas). I spend a lot of time in Texas. If you're interested in energy, you've also probably spent a lot of time in Texas or at least thought about it a lot.
It's basically a Texas history channel where you have great photos of old stuff in Texas, often including oil wells and things like that. But there's also really great nature stuff in there as well. For example, I was looking today at Traces of Texas, and I learned that at one time near where the city of Lubbock currently stands, there was a prairie dog colony that's spread over 37,000 square miles and included more than 400 million prairie dogs. As late as 1903, there were estimated 1 billion prairie dogs living in Texas. If you're interested in Texas and the environment, I think you'll enjoy Traces of Texas on Twitter. But how about you, Noah? What's on the top of your literal or metaphorical reading stack?
Noah Scovronick: Well, it's not reading, but it's listening in this case, sticking with the environmental theme. I wanted to recommend the Floodlines podcast. It came out in March of last year so it's new, but not super new. It's a multi-part series about Hurricane Katrina. And it does a really incredible job capturing the complexities of the event, the history leading up to it and the aftermath. Obviously it's highly relevant from an environmental and climate change perspective, but it also deals with a number of the social issues that contributed to the disaster. Many of those have been at the forefront of our national conversation over the past few years.
So it's super relevant and it really tells the story in a unique and really interesting way. I used the podcast in one of my classes so I've listened to it a couple of times now, and I continue to think it's a treasure, even though it's certainly not always an easy listen from an emotional perspective because of so much of the trauma and disruption that so many people experienced during and after that event.
Daniel Raimi: Yeah. I just looked it up. It looks fascinating. Floodlines from the Atlantic magazine. I will definitely check this out. Thank you for that recommendation. Well, one more time, Noah Scovronick from Emory University, thank you so much for coming on the show today and helping us understand your work and your colleague's work on the health impacts of climate change. We really appreciate it.
Noah Scovronick: My pleasure. I enjoyed it. Thanks for having me.
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