Radley Horton

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If we look at other things that kill far more people like having heart disease, or, you know, having really bad asthma, or also like renal kidney issues. People with those conditions die at a much higher rate on really hot days than they do on a typical day. But the problem is, it’s often not recorded that way.


Hello everyone, thank you for tuning into City Atlas Teen Cast. My name is Gabriel Gitter-Dentz, and I’m a rising senior from Hunter College High School and I live in Manhattan.


My name is Adam Rudt. I’m also a rising senior at Hunter College High School, and I also live in Manhattan.


My name is Kevin Zhou. I’m also a rising senior at Hunter College High School and I’m from Queens.


So, this is our second episode of our podcast. And we noticed that in our schools we don’t really talk that much about climate change. Maybe you’ll mention it in bio class, maybe we’ll talk a bit about it at a lunch table, but we don’t really have a set mode for discussion of climate change, especially for teenagers. So, this is what City Atlas Teen Cast is going to do.


On today’s episode we would like to welcome Dr. Radley Horton, who is also joining us from New York City. Can you introduce yourself, Radley?


Hi everybody, my name is Radley Horton, I’m a climate scientist at Columbia University. I study extreme weather events, and I’m very interested in trying to reduce the impacts of extreme weather on cities, communities, ecosystems, sort of all of the above.


We’re super excited to have you and hear about your work. You’ve been active recently, in writing papers right — we read a little bit of a paper that you wrote. Well, can you just talk a little bit about that?


Sure, yeah. So my research group at Columbia has been very interested in looking at heat waves, which are the leading cause of death among extreme weather events in the US, and actually, a leading force around the globe.   

And we kind of realized that when you look at weather reports, but also when you look at outputs from the climate models that we use to predict what’s going to happen in the future, they only focus on temperature when they’re talking about heat waves. Which kind of makes sense, right? Temperature is certainly the first thing that everybody thinks of. But what we realized in our research is that the old kind of cliche of, it’s not just the heat it’s the humidity, is critically important. We shouldn’t just be looking at temperature we should also be asking how much moisture is in the air, at the same time. Because that’s really the best predictor of whether people are going to overheat and get sick, going to be unable to do outdoor labor. 

It’s not enough just to know what the temperature is, we have to know when it’s hot, is the air also too humid to allow people to sweat efficiently to cool off. So in some of our recent work, we’ve been looking at historical weather data for trends, not just in temperature and temperature and humidity together, and trying to identify parts of the world that are already vulnerable to these really extreme humid heat days.


When we were looking at your project we — I think you kind of explained it a bit but is that is that what you mean when you say wet bulb temperature? Is that the type of temperature that takes into account both humidity and the actual temperature?


That’s exactly right. Wet bulb temperature is a measure you can use that captures both of those effects, and the way to think of a wet bulb temperature is basically, start with a normal thermometer that we’re all familiar with, but if you imagine at the at the bottom of that thermometer, that sort of rounded bulb, if you could somehow put like a wet cloth there, that was like permanently saturated that stayed sort of endlessly wet, how much would that drive down the temperature within that thermometer through the process of evaporation which cools things. So, if you had an endless supply of water, how much would evaporation cool down the temperature?

That’s essentially what the wet bulb temperature is. As I alluded to earlier, it’s a good predictor of basically how somebody who’s in good health, sitting in the shade with an endless supply of water, who’s not wearing too heavy clothing, who’s trying to sweat to stay cool. Will they be able to do that or is there so much moisture in the air, that the body can’t sweat effectively causing heat to sort of build up within the within the person and ultimately make them sick.


And when you say heat waves are the leading cause cause of death, do you do you mean in that direct form where we’re prevented from sweating and it causes them to get sick, or do you also mean in that increased heat waves can cause other natural disasters and that also causes death?


Yeah, that’s — I’m really glad you brought that up.

It seems like such a simple question — what does it mean to die from heat? But it’s actually, there’s a lot of debate about who should be counted as a heat-related death. I think everybody agrees that if somebody like overheats and gets like heatstroke if their body temperature scores really high and they die. That’s clearly a heat related death.

But the problem is, if we look at other things that kill far more people — like having heart disease, or, you know, having really bad asthma. Also like renal kidney issues. People with those conditions, die at a much higher rate on really hot days than they do on a typical day. But the problem is, it’s often not recorded that way. So, most people don’t realize that heat is actually playing a factor. It’s not the only factor. So, you’re absolutely right, it’s, it’s really necessary to think of the broader sets to identify, of causes, to identify all the, all the ways that people can die from heat.


So, you said before that there are specific parts of the earth that are tend to be more hot, as well as humid, and would have a higher [frequency] of wet bulb temperature. I think you mentioned parts of the Middle East and South Asia in the article. I was just wondering what is it about those places like the geography or topography, that makes them susceptible to wet bulb temperature?


So you guys are asking all the right questions, you know, it may seem sort of hard to believe but a lot of the scientists haven’t figured out the answers to all these questions yet so the types of things you guys are asking are sort of right at the right at the frontier. But I would say that when most of us picture like a hot and humid place. The first thought that might come to mind might be something in what we call the deep tropics somewhere you know really near the equator, Central Africa, Amazon, Indonesia somewhere like that. Right on the equator.

The typical day is very hot and humid. But what we found, which is kind of surprising is that to get these really extreme humid heat values that are much higher than even what you get in the tropics. You have to go to these places, especially in what’s called the subtropics which is the area where you actually tend to see dry air, where excuse me where you tend to see bright skies and where we think of there not being a lot of precipitation so this is like the latitude where you find, Arizona, or the deserts of Australia, even the Sahara Desert the Middle East.

It’s weird to think that these places could have high humidity and and high temperature, but the critical thing is if you’re at those latitudes, you don’t get a lot of cloudiness, you don’t get a lot of thunderstorms which can kind of mix the air and get the extreme humid air away from the surface — sort of mixed, and spread out in the atmosphere.

So, the worst conditions aren’t right along the equator, if we’re talking about the sort of worst day per year, they’re more in these subtropical areas where it doesn’t rain a lot.

Now you guys are probably thinking, this guy’s crazy everybody knows the deserts aren’t aren’t humid, but the critical thing is that it’s when you find a water body in these kind of subtropical areas. So for example, you know just below Arizona there’s the Gulf of California, that little area of water between Baja, Mexico and mainland Mexico. Similarly, if you think about sort of between like Iran and Saudi Arabia, there are these bodies of water there too. They’re relatively small. If they’re just exposed to intense sunlight, they can heat up like crazy by the end of the summer and actually get to a point where the water temperatures are above 95 degrees Fahrenheit, in some cases.

So that’s the right ingredients, a warm source of water, but overall conditions of bright sun that would be actually associated with the desert. Those are the right circumstances to get these crazy combinations of heat and humidity. And as you said they do extend into India as well which, you know, has has some of those same characteristics, but more importantly just has a huge population, right, it is going to be the most populous country in the world pretty soon and there’s there’s a lot of vulnerability there as well.


So in your paper you talk about monsoons in South Asia, and we’re just wondering if you could delve more into causes behind it, the effects of it, and how it can impact wet bulb temperature.



Yeah, so the monsoon is like one of the most sort of powerful seasonal cycles anywhere on the planet. And basically what happens is, for about six months of the year, the winds primarily blow to the north and somewhat from the southwest towards the northeast, towards places like India, Nepal Bangladesh, Pakistan. And in general, the winds are blowing from the southwest to the northeast in those areas once the sun has gotten pretty high in the Northern Hemisphere, so when we’re in month like around now, May, June or July. The bright sun, over 12 hours a day of direct sunlight on the landmasses, causes them to warm up more than the water to the south can warm up just because land has a higher heat capacity. It can warm up per unit of energy from the sun faster than the ocean can. So as you warm the land, hot air is going to be less dense than air that’s slightly cooler.

So you warm up that land, there’s going to be a tendency as the surface heats up for air to start to rise near the surface. As it rises, it has to get replaced from somewhere else. And it basically gets replaced from that flow, near the surface of winds from the south. And those are winds that have been blowing over the water to the south of places like India. That’s very warm water. So, as the winds are blowing they pick up a lot of moisture that they then bring towards you know places like India.

That process continues until the sun starts to move closer to the Southern Hemisphere, then you don’t have the land, heating up strongly anymore. You don’t have that rising air. Instead, you have a tendency for a kind of sinking air, and the winds reverse.

So the monsoon is basically the driver of the rainy seasons and helps support arguably like 2 billion people in South Asia. The interaction with wet bulb is kind of complicated. Basically what we see, for the most part, is that the wet bulb temperatures in India seem to be about the worst right as we start to transition, basically just as the monsoon season is getting going before the rains start. Things have been heating up, heating up. Then there’s a point where you’re starting to get that flow of winds from the southwest to the northeast, just enough to pile moisture up, but a little before it actually starts to get cloudy and rain heavily. That build up period seems to be the sweet spot where the wet bulb temperatures get really high. And eventually, it starts raining like crazy. Still humid but it’s not that kind of like lethal humidity because it’s cloudy. The rain is providing some moisture and sort of mixing up the air.


So, let me just backtrack a little bit, to where could have we started this. How are our carbon emissions contributing to this state of high wet bulb temperature that you say is dangerous?


Yeah, with all of these things related to climate change it’s important to start with the idea that a lot of these extreme weather events, always existed before we started putting more greenhouse gases in the atmosphere. We’ve always had heavy rain, we’ve always had coastal flooding and heat waves. But what happens is we put more greenhouse gases in the atmosphere and we now have 45% more carbon dioxide in the atmosphere, due to our activities, than we did 250 years ago when the industrial revolution started.

What that’s done is it’s loaded the dice, as we’ve warmed air temperatures, as we’ve caused sea levels to rise. We’re basically loading the dice where it’s much more easy now to get a very hot day, and a very humid day than it was before.

So, we’re seeing far more. And we looked at trends in the paper and in wet bulb temperatures around the world, and found that they’re twice as many days now, crossing some of these dangerous thresholds of heat and humidity, than there were just like, you know, a generation ago, basically 40 years ago. So the little bit of global warming we’ve had, which may not sound like much, has already had a huge impact on how frequently we get these extreme humid heat events, and it’s opening the door to these unprecedented extremes, that we never used to have before, where no matter how much you sweat, you can’t stay cool enough, or anyone who doesn’t have air conditioning is going to suddenly face life or death issues.

There’s probably implications for other types of mammals too, overheating. So those are those are some of the kind of things we’re thinking about and it really is directly related to our fossil fuel emissions right? The cement making, the deforestation, the tailpipe emissions, you know, you name it, due to our activities making the problem much worse.


That’s actually absolutely insane to me. Because normally people think of climate change and carbon emissions as maybe increasing the sea level. And the effects don’t seem…they seem pretty specific and I guess, tangible. Like a city will go underwater, or people will have their crops wiped out. But to have that connection between climate change and something like you were mentioned before, heart attacks increase on on days where there’s high wet bulb temperatures is…yeah…


No, That’s right I totally agree with you, and it’s it wasn’t really appreciated until recently, so it’s gonna affect all sorts of things right? Like ability to do outdoor sports during the middle of the day, farmers being able to collect crops, just to name a few people in the Persian Gulf who do the annual rite of passage, the Hajj or the pilgrimage to Mecca. All that sort of thing. So it’s a blend of health, economic, cultural, it’s just kind of like triple-whammy or more.

Partly it’s the air temperatures going up. Also it’s the oceans getting warmer, due to all the fossil fuels we’ve emitted so that warmer ocean just means more moisture can get evaporated into the air, and you can get these incredible combinations of humid air that causes wet bulb temperatures. And probably also just as an aside, mean that when the conditions are right for rainfall, you get these crazy heavy rain events right because there’s just so much moisture in the air, when it finally does rain.


So, kind of transitioning. What countries would you say are doing a good job right now, and have the right policies to prevent or limit, the dangerous effects of high wet bulb temperatures?


The overall question in which countries are reducing their greenhouse gas emissions enough, you know, which is a global issue right because the greenhouse gases are mixed and stay in the atmosphere forever so every country has to reduce…sadly there’s very few countries that are that are doing enough in that respect, maybe a few places like Denmark.

Arguably, some of the Scandinavian countries, although there are cities [and states] like California and New York that are moving in the right direction.

But your question is more about how do we adapt to the actual wet bulb extremes in these places, who’s doing the best on that?

And that’s a really good question. I think in general, probably nobody’s doing enough, one of the one of the tricky issues that we have to acknowledge though, is air conditioning, right? Because if you immediately want to protect people from these conditions, air conditioning is going to be critical. And in a lot of the big wealthy cities in the Persian Gulf and the United Arab Emirates, Saudi Arabia, a lot of the population has access to air conditioning. Does everybody? Do some of the migrant laborers who don’t, you know, get a lot of attention, are some of them suffering? Working outdoors? Maybe, but it’s hard to get that data, but in general, there’s a lot of air conditioning. Which, in one sense really protects people and really frankly is essential.

But that’s tricky, right? Because how do we do that air conditioning without blowing the global carbon budget? Can we use renewable energy to provide that air conditioning? That’s a critical question. And unfortunately, precisely when the temperatures are really high and the humidity is really high. Just like people suffer these nonlinear impacts where an extra degree matters a lot, so too the amount of energy that you need to do air conditioning goes up dramatically as well. So unfortunately, the amount of energy demand to stay cool in these conditions is really, really high.

Other things towards your question — are outdoor laborers being protected? Are people doing construction given like vests that can help them stay cool?

Are they trained in multiple skills so they don’t have to be outdoors during their whole period of work? Those would be other kind of critical factors.

I feel like there’s some progress on that in the US. I think the short answer is, nobody’s doing enough to address this issue, but we have to acknowledge that the countries that have more air conditioning, have a little less danger of people overheating, even though they’re contributing a lot to the problem through the air conditioning, right, of global warming. It’s very tricky.


Thank you for listening to episode two stay tuned cast which was the first part of our talk with Radley. We really enjoyed talking to him about wet bulb temperatures, their negative effects on people. And, you know, the core reasons behind why wet bulb temperatures can get as high as they do and why certain regions are more dangerous than others. Thank you and make sure to tune into future episodes.