Heat is a ‘silent killer’

January 24, 2019 — Climate change will mean more extreme weather, including heat waves. And it’s not a distant threat—we’re already seeing the effects now in the United States. In this week’s episode, we explore the health threat posed by severe heat and how our society needs to adapt in the decades ahead. You’ll hear from Augusta Williams, a doctoral student at Harvard T.H. Chan School of Public Health, who studies how extreme heat can affect our bodies and minds. She’ll explain why heat is considered a “silent killer” and how we can combat the effects of our warming world.

This episode was produced with assistance from Veritalk, a podcast from Harvard University’s Graduate School of Arts and Sciences.

You can subscribe to Harvard Chan: This Week in Health by visiting iTunes or Google Play and you can listen to it by following us on Soundcloud, and stream it on the Stitcher app or on Spotify.

Learn more

Extreme heat linked with reduced cognitive performance among young adults in non-air-conditioned buildings (Harvard Chan School news)

How ‘heat islands’ can harm health (Harvard Chan School news)

Full Transcript

AUGUSTA WILLIAMS: So my research all focuses on the impacts of extreme heat on human health. A lot of my research is focused here in Boston and Cambridge, which is fun. And then we further examine the influence of the built environment and its role in either mitigating or exacerbating extreme heat exposures and the resulting health impacts on the populations of Boston and Cambridge.

ANNA FISHER-PINKERT: Can you tell me a little bit about, like, why is heat bad for our health?

AUGUSTA WILLIAMS: So heat is one of the most well-understood public health impacts of climate change. There’s been a wide variety of research that has shown that heat is one of the largest killers of all meteorological phenomena, more so than floods or tornadoes and hurricanes, which a lot of people are surprised by since a lot of those other weather events look much scarier than extreme heat does. But it’s really a silent killer is what a lot of public health researchers call it because you can’t see it.

But it’s extremely dangerous. There’s been a lot of research that has shown that heat has a role in exacerbating cardiovascular disease, respiratory health outcomes, even renal in diabetes complications, outcomes related to pregnancy and the health of newborn babies, and even things like our cognitive function, our sleep, and our productivity. So there’s a wide range of health outcomes that heat influences and really across all sectors of society.

ANNA FISHER-PINKERT: Tell me some of the medical conditions that could be exacerbated by heat.

AUGUSTA WILLIAMS: So things like cardiovascular outcomes related to either heart attacks, or heart failure can be complicated during extreme heat exposures. People with diabetes are more prone to heat stress or have complications related to their diabetes condition. Respiratory outcomes, especially asthma– that’s an important one, because also during heat waves, there’s usually high air pollution rates that also then trigger asthma, especially in vulnerable populations, like children and the elderly.

ANNA FISHER-PINKERT: So you mentioned earlier that there are these cognitive effects of heat. What do we know about that?

AUGUSTA WILLIAMS: So there’s been some great research happening here at Harvard on this, as well as elsewhere. My team recently published a study that was led by Dr. Memo Cedeno, where we actually worked in the dorms here on campus at Harvard and tracked students for 12 days. Half of the students we worked with had access to air-conditioning in their dorm rooms, and the other half did not.

And we found that during this time, we were able to see before, during, and after a heat wave. And those without air-conditioning experienced significant reductions in their cognitive performance. And we measured that with two tests. One was a color word test that the students completed, and the other was an addition and subtraction test. And on both of these, saw impairments in their performance when they didn’t have access to air-conditioning during the heat wave.

ANNA FISHER-PINKERT: What’s a color word test?

AUGUSTA WILLIAMS: So that test is one that you see a lot in a variety of forms on the internet. It’ll pop up where the word is written in a certain color, but the word is also a color word. And you have to determine what color the word is written in.

So the word might be “black,” but it’s written in blue ink. And you have to pick that it’s the color the ink is, is blue. So kind of getting at some complex cognitive processes.

ANNA FISHER-PINKERT: Although when you say complex cognitive processes, it’s not like we’re asking them to do, like, calculus.

AUGUSTA WILLIAMS: No, not at all. I don’t even think I would be able to perform well on that test without the heat exposure. But looking at some of the ways our brain, our active memory, the way we’re able to process words and numbers can have relationship to the decisions we make when we maybe leave for work. We get in our car, and we commute to our job or to school, or if you have a test to take– some of those similar things.

And this was supported by other work. There was a study that Jisung Park did during his time here at Harvard, showing that students in New York State who took a Regents exam on a 90-degree day versus a 72-degree Fahrenheit day performed worse. And looking at how heat really can play a role in short and long-term learning and thinking.

ANNA FISHER-PINKERT: So I can see why that’s a problem if you’re a student and you need to pass your Regents. But, I mean, if we just have a slightly less cognitively smart population in a city, what are the consequences for that?

AUGUSTA WILLIAMS: I think it can have consequences that may be more immediate in terms of maybe people are making poor decisions in the morning, because our work was really looking at these tests happened right after waking up. So kind of looking at overnight temperatures, what is the role of these extreme heat exposures indoors during your sleep periods on your ability to wake up in the morning and, you know, how active your cognitive thinking is? But there’s a lot more research that’s needed to determine what are the long-term effects of this.

How long into the day do these processes happen? Is this an acute or a more long-term effect that heat has on our thinking and performance? But looking at how the economy and how many of our workplaces are still currently functioning, if we look at extreme heat and the role that would play on those, there may be wider effects on larger sectors of the population than previously thought.

ANNA FISHER-PINKERT: In terms of, like, cognitive impairment, why is that a public health concern?

AUGUSTA WILLIAMS: So when we think about the role heat plays on our cognitive function, there’s a lot happening in our brain that can have outward-facing effects on society, whether that’s how we are performing at work or school. There’s a lot of research showing that on hot days, there’s increased aggressive and violent crime in many urban centers. There’s even a newer area of research looking at car accidents happening on hotter days, that our brain’s ability to make decisions, reducing our risk-taking behaviors are all inhibited as temperatures increase. So there’s a lot of outward-facing effects on society that this heat and cognitive function relationship can have on the public.

ANNA FISHER-PINKERT: So tell me a little bit about how climate change plays into this story.

AUGUSTA WILLIAMS: So with climate change, heat is one of the largest climate change outcomes that we’re seeing, especially here in the Northeast United States. There were a lot of really important landmark climate-change assessments that came out at the end of November, beginning of December that are showing that the heat story is only worsening in many parts of the world, unfortunately. Here in Boston, we typically have about 11 days per year that are above 90 degrees Fahrenheit, looking at the last 30 to 40 years of climate averages.

But by 2030, that number is expected to grow to potentially 40 days above 90 degrees Fahrenheit. And by 2070, that number is expected to be almost our entire summer could be above 90 degrees Fahrenheit, with a significant portion of that even above 100 degrees Fahrenheit. So some comparisons that were outlined in these reports is that by the middle of the century, Boston could have summers that currently look more like Washington, DC, but towards the end of the century, more like Birmingham, Alabama.

ANNA FISHER-PINKERT: So I came here from Washington, DC. And I can tell you, I do not want to live through those summers.


AUGUSTA WILLIAMS: You came to escape–



ANNA FISHER-PINKERT: Yes. So that sounds pretty dire. Are there specific concerns? First of all, I guess my question is, is this worse in cities?

AUGUSTA WILLIAMS: Yes, heat can definitely have a larger burden on urban centers because of the urban heat island effect. And this is because of the way urban centers are structured, we have a lot of high-rise buildings close together that are made out of materials that really absorb a lot of heat. And because of this and other sources of heat– like we have more cars that are exhausting their air into the cities– you can have upwards of a 10, sometimes even a 20-degree Fahrenheit temperature difference between an urban center and surrounding areas. And that depends on the day and the structure of the individual city but can range anywhere up to 22 degrees Fahrenheit, some researchers have found.

ANNA FISHER-PINKERT: Are there specific impacts for a city like Boston versus a city elsewhere in the country?

AUGUSTA WILLIAMS: So the impacts in the Northeast are showing that heat waves are increasing in frequency, intensity, and duration. So in places like Boston and New York and Philadelphia, heat’s going to become more of an issue. And as a result, on our current greenhouse gas emissions trajectories, they’re looking that heat-related mortality could upwards of triple by the end of the century, which is really scary.

But I think heat is increasing in all places across the world, that this is not a story unique to the Northeast. Something that is more unique to the Northeast is the fact that a lot of our buildings and our building stocks were created for the cold winters that we also have and will continue to have, that we have very low rates of central air-conditioning penetration. And studies have found that of all types of air-conditioning, central air-conditioning is really the one that helps most combat and reduce the high thermal loadings of indoor environments during heat waves. So that’s something that more on the adaptation side, the Northeast is more unique than other areas like the South, that has a much higher rate of air-conditioning at home.

ANNA FISHER-PINKERT: What’s a high thermal loading?

AUGUSTA WILLIAMS: So high thermal loading is when a building just has the ability to maintain a high thermal mass– lots of temperature– whether that be from it’s made out of materials that absorb a lot of heat, it’s oriented in a way– like the building I live in is a south-facing building made of brick. So it’s just hit by the sun all day and made of materials that really maintain that heat, which is great in the winter this time of year but not so helpful in the summertime.

ANNA FISHER-PINKERT: I mean, aren’t our winters also supposed to get worse over time, too?

AUGUSTA WILLIAMS: Yeah, so I think our winters, for the most part, as average global temperatures increase, there will be a slight warming throughout the entire year. But extreme cold will still be a thing that is happening here in the Northeast and elsewhere across the globe. So extreme cold spells and cold waves, which also have their own set of public health impacts, will also continue to be important. So there’s some really unique adaptation problems that we’re facing of how can we adapt these urban centers to still continue to experience both extreme heat and extreme cold, more so than historically we faced here in Boston?

ANNA FISHER-PINKERT: So it seems like the thing that’s getting cut out of the calendar are those, like, nice sunny days in June and September when you can just kind of walk outside in a T-shirt and jeans.

AUGUSTA WILLIAMS: Yes, those are my favorite.


ANNA FISHER-PINKERT: Well, and they’re going away.


ANNA FISHER-PINKERT: Uh, OK. So I want to talk about air-conditioning because what you’re saying is that air-conditioning really helps with these public health outcomes. But isn’t that also a contributor to climate change?

AUGUSTA WILLIAMS: Air-conditioning is a really challenging problem right now. Air-conditioning is a vital public health tool. It saves lives. It keeps indoor spaces cool, which is very important for vulnerable populations.

But at the same time, air-conditioning has a few problems. The first is that in many areas in the United States, the energy generated to run these air-conditioners is generated by fossil fuels. And during those times, there are significant increases in the air pollutants that the fossil fuels generate that, both whether it’s carbon dioxide, which contributes more to climate change, or things like sulfur dioxide and nitrogen oxides that have really significant public health impacts, that both of these things threaten the health of communities, either by the direct air-pollutant exposures or through exacerbating climate change, and therefore worsening our heat problem so that we need even more air-conditioning to begin with.

But then at the same time, air-conditioners are also one of the largest sources of certain refrigerants. The cooling mechanisms that are inside of air-conditioning actually have huge greenhouse gas potential. They have the ability to warm even more than carbon dioxide.

And whether those are leaking, they’re not being efficiently used, or when people get rid of them, they do so in a way that these gases then leak out of them, and go back into the atmosphere, and then further contribute to climate change, leading to more heat. So air-conditioning is a really complicated problem that I think, for the most part, we have great technologies that could help us solve these issues so that we could use more air-conditioning in a sustainable way.

ANNA FISHER-PINKERT: Can you tell me about some of those technologies? Because I’m thinking, like, all right, I’m listening to this. And I’m trying to, like, build a new building. What am I supposed to do?

AUGUSTA WILLIAMS: Right. So some of the problems from air-conditioning we have the technology to solve. Right now, the Kigali Amendment to the Montreal Protocol would help us reduce the amount of refrigerants in the air-conditioning and other cooling systems across the world. It would help us mitigate upwards of 0.5 degrees Celsius of warming by the end of the century, which would be huge.

We would be able to use these air-conditioners without the negative climate potential of the gases inside of them. However, the US has not yet ratified that amendment. So that’s a step we could take and is one that both all the political parties, as well as industry folks, are supportive of because it would allow more air-conditioning use in a more sustainable way.

And then the second is to increase our use of renewable energy. If we are running air-conditioning on energy that is not producing harmful greenhouse gases and air pollutants, we can then mitigate the role air-conditioning has in worsening climate change. So I think those are two real key solutions that we have the ability to do better and to do more if we want to move in that direction.

ANNA FISHER-PINKERT: Is there a health consequence to people staying indoors in climate-controlled environments for more hours during their day?

AUGUSTA WILLIAMS: Yeah, I think that’s a great question. There’s been a lot of research– upwards of 40 years of research– looking at the role of indoor environments and indoor environmental quality on human health, whether that’s in our homes, or at work, or at school. I’m a member of the Healthy Buildings Team at the T.H. Chan School of Public Health. And that’s really our purview of looking at anywhere we live, work, or play.

What is the role of the indoor spaces that we’re existing in on our health? And temperature and thinking of thermal health is a really– there’s a sweet spot for getting thermal health conditions somewhere where you’re not using a ton of energy, where you’re able to cool spaces and create enough ventilation that indoor sources of pollutants are able to disperse, but also so that you’re not overheating or over-cooling the people that are existing in these spaces, and doing so in a way that health is maintained and productivity and performance are as well. And with certain populations like the elderly, they have different heating and cooling needs and comfort levels than, say, you know, young 30-something adults working in an office building.

ANNA FISHER-PINKERT: So as someone who is, like, relatively healthy and in– maybe I don’t need air-conditioning, like, am I doing good for the world by shutting it off when I can?

AUGUSTA WILLIAMS: I think finding that balance for you personally of conserving energy, not using air-conditioning when we don’t really need it, using more natural sources of ventilation, whether it’s using windows or fans, can be better. But as temperatures rise and get to more dangerous levels, I think that’s when it becomes harder to rely on those sources of ventilation. Even if we’re feeling OK, I think some of the work on the cognitive function has showed that without those cooling sources, even if we’re feeling OK and feeling fine, there might be internal processes that are being negatively impacted by heat. So we really need to do more work in figuring out where are these thresholds for different sectors of the population when it comes to thermally healthy and comfortable indoor spaces.

ANNA FISHER-PINKERT: I also wanted to ask you how inequality in a city plays into this.

AUGUSTA WILLIAMS: Yeah, that’s one of my biggest interests and passions in looking at climate change adaptation, of thinking of environmental justice communities and communities that may have the social demographic disadvantages that relate to them– these populations– being more vulnerable to heat, whether it’s more elderly people or people of low to no income who can’t afford an air-conditioner or afford the energy to run their air-conditioner, who maybe do not speak the native language of that area. For Boston, it would be English– that a lot of the heat warnings are disseminated in that language. And they might not be able to access that information.

When we think of access to cooling, cooling centers are a great resource but are not located in every community. Or say someone cannot physically get to the cooling center. Boston has, luckily, done some great work at increasing free transportation to these centers and things like that.

But we definitely have a long way to go, especially my work focusing on the built environment, that perhaps in those communities we’re doing some really great messaging around getting the word out about heat dangers. But we could do more in offering energy assistance for cooling, like we do for heating purposes in the winter, to do more about focusing on these communities where we’re planting our trees, where we’re painting our roofs lighter colors to help reduce the thermal loads of these communities.

ANNA FISHER-PINKERT: Yeah, I imagine, like, as you were describing, these older buildings that are close together have those high thermal loads. So I would imagine a neighborhood without green spaces, where buildings haven’t been renovated in several decades– those are places where people with less privilege often live.

AUGUSTA WILLIAMS: Yes. That is definitely very common in a lot of urban areas, that access to green space and parks or little splash pads, as well as neighborhoods that are made of materials that just keep those communities cooler to begin with, as well as not having the income to sustain air-conditioning use throughout the summer are usually very well co-located. Part of my research moving forward is to do an in-depth assessment related to all those variables I just mentioned, as well as building characteristics, to look at the role of these built environment factors on the vulnerability of communities in Boston to see if there’s areas where we could better strategize the types of adaptation measures or public health campaigns that we’re doing. So I’m excited to dive into that and see what we find, and see where we can better prioritize certain communities that need some of this adaptation work the most and the soonest.

ANNA FISHER-PINKERT: I thought it was interesting, also, you talked about incentivizing people to make changes to the built environment by repainting roofs, adding greenery. We kind of do that for solar panels. But is there a model for doing that for things that reduce heat?

AUGUSTA WILLIAMS: I haven’t yet seen a model about the incentivizing cooler communities yet. But it’s something that I’ve been to a couple of talks throughout the city of Boston this year in the last few months and have heard early discussions of that, both related to heat and to sea-level rise and storm flooding, of how can we think of as Boston continues to grow and expand, prioritizing climate resilience as developers move in, or as existing structures need to be updated and need to re be renovated? How can we think about providing incentives and allowing developers who want to be resilient in the face of climate change to get some type of reward so that it’s more market based, that we’re helping these developers continue to grow, continue to positively impact the Boston area, but in a way that doesn’t set us up for more problems in the future?

ANNA FISHER-PINKERT: I think it’s, like, it’s somewhat of a tight spot, right? Because you have developers who maybe aren’t going to be tied to that community once the buildings are built and the people have moved in. And then you also have citizens who aren’t necessarily, as you said, aware of the dangers of heat because it is silent. It’s not the same as having a nor’easter come through town or having a hurricane come through town. How do we get past that hurdle?

AUGUSTA WILLIAMS: I think that’s a great question, and one a lot of scientists working in this space are grappling with right now. I know on our team, we work with a very interdisciplinary team of folks. We have urban planners and architects and engineers on our team and have built close partnerships with both the developers, real estate companies, the people running and managing the buildings, and are trying to translate our science in a way that allows all of these stakeholders to understand the health impacts of the buildings that they are creating and running, and how they play a huge role on our health, perhaps equal to our more than our actual physicians and doctors do. Because we spend upwards of 90% of our time indoors, these people need to be part of the equation. And they’re extremely receptive to this information of how can we better work together to prioritize health in the face of climate change, in all of these structures that really play such a huge role in our lives.

ANNA FISHER-PINKERT: One thing that’s a theme in all of the stories I’m talking to people about– one thing that’s come up a lot is who controls the destiny of your city? And it seems like when it comes to climate change, it’s out of our control. Is there a way that we can take back control over what’s happening?

AUGUSTA WILLIAMS: I think if we continue to think about the ways we can adapt to climate change, the ways we can mitigate climate change from occurring, a lot of that action is happening at local levels, at the city levels. I think Cambridge and Boston are really leaders in a lot of areas when we look at other cities across the world, that we have people who are really dedicated to these causes, as well as leaders who are dedicated to these causes. And perhaps the steps that are taking, people can disagree on. But I think we’re all motivated by moving forward, whether that’s switching to renewable energy to mitigate greenhouse gas emissions, or thinking of ways we can better retrofit the downtown area to protect against sea-level rise, to planting trees.

Cambridge just got a huge grant. It was a participatory budget grant that the residents of Cambridge voted for. And the top result of that was to plant trees across Cambridge. So I think this is a really hopeful place to be, that we cannot necessarily control the warming that’s been set into place today, that we are experiencing more hot days. But we do have a role as citizens living in these areas, and also in partnership with the leadership of the area you’re living in, to take steps to mitigate and adapt in ways that are most beneficial to your community.

ANNA FISHER-PINKERT: I think it’s interesting. It’s like a lot of these adaptations are just things that people would like to have anyway.


ANNA FISHER-PINKERT: So I’m sure some people voting for planting more trees in Cambridge just like trees. Like they’re not thinking about heat.

AUGUSTA WILLIAMS: Exactly. And there’s so many ways. I think there’s a comic about that of, well, what if we create more parks, and reduce air pollution, and make the air cleaner? And it’s all just to make a better world, that it will improve the climate-change problem and the health benefits we see in the future. But it also will make our world a better place. And I think that’s a great kind of part to the equation.

ANNA FISHER-PINKERT: Right. Right. You don’t have to be, like, a climate-change activist to think that it’s a good idea to live in a city with green spaces.


ANNA FISHER-PINKERT: So what motivates you personally to do the work that you do? Why do you– I ask a lot of people this. Like, why do you get up in the morning and go do this work?

AUGUSTA WILLIAMS: That’s a great question. I’ve always been really motivated and passionate about health. And kind of it came more from an infectious disease standpoint, even though that’s not at all the work I’ve ever been directly involved in or do today. But looking at how health burdens can spread throughout society, whether that is through an infectious means or other things, like the health impacts of climate change that are impacting societies at a huge scale.

And I have always been really drawn and motivated by the fact that the science we can do, the actions we can take can have a ripple effect on entire populations and shift the burden of health in a positive direction, bring everyone together with you, as opposed to working on the health of one individual at a time, which is extremely important. But I’m more drawn by shifting the curve for all kind of simultaneously.

ANNA FISHER-PINKERT: It sounds like what you’re saying is, like, we tend to think about, like, an individual’s, like, healthy choices. And that’s how their health is going to improve, as opposed to saying, like, let’s look at the whole city. And does it function in a way that creates health for everybody?

AUGUSTA WILLIAMS: Exactly. In environmental health, many of the huge public health successes that have come throughout our time in a civilized society have been related to environmental health, which is really exciting to me, or other areas of public health. When we think of sanitation and kind of the strides we’ve made in that. Seat belt laws is another one that is a huge public health achievement that has saved countless number of lives, that when we think of the wins we’ve had over time and kind of where we’re headed in the future, I think climate change is really the next big one that we need to tackle. But through public health and interacting with all other sectors of society and important stakeholders, I think we can shift that curve in the correct direction.

ANNA FISHER-PINKERT: I think it’s interesting because probably if you asked someone– if we were doing this interview before the advent of urban sanitation, it would have also seemed like an intractable problem. Like, well, how are we going to get rid of all this waste? That’s not possible.

AUGUSTA WILLIAMS: Exactly, and was another one that required a lot of different stakeholders to come together, because the problem was the health burdens that were being faced by these society members. But you needed the engineers and the urban planners and the city managers to all come together and work through this health lens to solve this public health problem. And I think that’s an interesting comparison to many of the issues that we’re facing today, and even more stakeholders that might need to come to the table to solve some of these.