Watch the replay of this event held on October 26, 2022. (Transcript below.)

Cities around the world have experienced record-smashing heat waves over the last few years, causing millions of heat-related illnesses and deaths.

Protecting people from extreme heat in cities will be one of the central challenges of climate adaptation in the 21st century. At the same time, many cities have pledged to reduce their carbon footprints — even as the need for air conditioning expands — in an attempt to hit net zero by 2050.

How can cities balance the need to cool off with the urgent imperative to reduce carbon emissions? On October 26 at 9 a.m. Pacific and 12 p.m. Eastern, join Annual Reviews, Knowable Magazine and Future Tense for a conversation about how we can make cities cooler — and save lives — without further heating the planet. And, if you can’t join us live, please register for access to the on-demand playback delivered to your inbox.

Attendees will learn:

  • What causes the urban heat island effect and why it disproportionately affects people living in poverty, the elderly and minority groups.
  • How green infrastructure can help to lower urban temperatures and protect biodiversity.
  • Why transparent, accurate data are crucial to reducing cities’ carbon emissions and reducing health impacts from heat waves.


Kate Gallego

Mayor, Phoenix, Arizona

Mayor Kate Gallego is dedicated to making Phoenix the most sustainable desert city in the United States. She has fostered investments in cool solutions, including the nation’s first publicly funded Office of Heat Response and Mitigation; launched the city’s successful cool pavement pilot; and led efforts to build infrastructure for electric vehicles. A graduate of Harvard University, she earned an MBA from the Wharton School of Business at the University of Pennsylvania. Prior professional pursuits include strategic planning and economic development for one of Arizona’s largest utility companies and service in state government as part of the governor’s team.

Angel Hsu

Assistant Professor, University of North Carolina-Chapel Hill

Climate scientist Angel Hsu studies how cities around the globe are driving climate change — and what they can do to fix it. As the principal investigator of the Data-Driven EnviroLab at UNC, she uses data analytics to understand how urban heat affects people around the world and to quantify cities’ carbon emissions, gleaning insights that can inform policy interventions. She previously led the World Resources Institute’s efforts to develop corporate greenhouse gas accounting and reporting initiatives in developing countries, including China. She is also an author on the sixth International Panel on Climate Change Report.


Henry Grabar

Correspondent, Slate magazine

Henry Grabar writes about cities for Slate. He is the author of the forthcoming book Paved Paradise: How Parking Explains the World.


This event is part of an ongoing series of live events and science journalism from Knowable Magazine and Annual Reviews, a nonprofit publisher dedicated to synthesizing and integrating knowledge for the progress of science and the benefit of society.

Future Tense is a partnership of Slate, New America and Arizona State University that examines emerging technologies, public policy, and society. Sign up for Future Tense’s newsletter.


More from Knowable Magazine

Related Annual Reviews articles

More from Slate

From the audience


Emily Underwood: “Hi, everyone. Welcome to our 20th live online event, ‘Rethinking cities in the face of extreme heat.’ I’m Emily Underwood, the producer of events for Knowable Magazine. This is a special event brought to you by Annual Reviews, Knowable Magazine and Future Tense, a partnership of Slate, New America and Arizona State University that examines emerging technologies, public policy and society. This is part of a three-part series on climate adaptation that we’re doing in collaboration with Future Tense, and our next event will be on the future of climate finance, so please stay tuned for that. If you haven’t checked out Future Tense before, you’ve got to do it. Sign up for their newsletter. And while we’re on the subject, Knowable’s newsletter’s pretty great too, so sign up for that. We have a lot to cover today so I’m going to hand this off to our guest moderator, journalist Henry Grabar in just a minute.

“But before that, please note the following housekeeping items. We’re going to be recording this. As always, you can replay it after it’s over, and we hope you will share it with others. If you find you can’t hear the audio, please refresh your browser and make sure the mute button is off. If one of the speaker tiles goes black — this is a known quirk — refresh your browser. Put your questions in the question box at the right of the screen on the bottom. After about 40, 45 minutes of discussion, our editors are going to pick from the question list and we’ll answer as many as we can in 20 minutes.

“So, without further ado, please welcome our guests and our moderator. First, we have Mayor Kate Gallego of Phoenix, Arizona. Mayor Gallego is leading efforts to make Phoenix — where temperatures frequently hit triple digits — cooler, safer and more sustainable. We also have Dr. Angel Hsu of the University of North Carolina at Chapel Hill with us. She studies how urban heat affects people around the world and how cities can respond without making climate change worse. She’s a prolific author and has written some fascinating Annual Reviews papers on net-zero cities, which our team will post in the chat along with lots of great other Annual Reviews content.

“Now, I’d like to introduce our guest moderator, Henry Grabar, who writes about cities for Slate and Future Tense and who just published a new book on a major contributor to the urban heat-island effect, parking lots, called Paved Paradise. Check it out. Over to you, Henry.”

Henry Grabar: “Thanks very much for the introduction, Emily. A small point of clarification, the book will be published next May. And without further ado, I want to also welcome Mayor Gallego and Dr. Hsu. We’re going to hear two different perspectives today on how to deal with extreme heat. Mayor Gallego obviously is dealing with extreme temperatures in Phoenix and could talk about what her administration is doing to protect 1.6 million people from extreme heat now and in the future. And Dr. Hsu will share what she’s learned from studying how people experience heat in cities around the world and some of the different approaches that those places are taking to respond and mitigate extreme heat.

“I want to start by focusing on Phoenix. Maybe, Mayor Gallego, you could give us an idea of what it’s like to live through an extreme heat wave. I know you grew up in New Mexico, and you’ve lived in Phoenix for over a decade, so you’re no stranger to the desert or hot weather. But what was this latest summer extreme heat wave like for you and your constituents? And how is it changing from what you remember, either from your childhood or even from more recent times?”

Kate Gallego: “Thank you. It’s wonderful to be with you here today, and I’m so grateful that people all over the world are joining us for this conversation. If we’re talking about solutions, we’re going to spread good ideas and hopefully really address a very serious problem.

“Phoenix is hot and getting hotter. This June, we saw at Phoenix Sky Harbor Airport a pretty significant monthly average temperature increase of 2.8 degrees in July, 1.9 degrees above our average. It is different than when I was growing up in New Mexico. I was born in Albuquerque. There was a mountain just outside of Albuquerque where there was a snow play area and skiing. The mayor tells me he thinks that skiing is just not going to be viable in the long term now because of warming climates. That is a reality for all of us.

“People in my desert city try to adapt to it. Even if there’s just a small amount of shade, you will find people gravitating towards that to try to adjust. We are coming up with different designs, which hopefully I’ll get to talk about, for both city level and individual buildings. But there’s no doubt it is getting warmer. And particularly for those who are most vulnerable, it can be dangerous.”

Henry Grabar: “Yeah. Let’s talk a little bit about the science behind this. Dr. Hsu, why do big cities like Phoenix get so much hotter than the surrounding areas where there’s less development? Can you walk us through this?”

Angel Hsu: “This is a really great question, and thanks so much to Mayor Gallego for sharing those personal experiences.

“Cities around the world are getting hotter primarily due to the urban heat-island effect, and that’s the temperature difference between an urban area and a background rural surrounding. And so when you have natural landscapes, forested areas, grassy pastures being converted into built environments —think about asphalts and pavement, buildings, roadways — all of this has the effect of being able to trap more heat in these materials compared to trees and grass, which actually transpire and can cool the air around them.

“What’s interesting about Phoenix, actually, I was looking at some of our data. We use a lot of satellite remote sensing data to measure this urban heat-island effect to measure how much hotter cities are than their background rural surroundings. And in some cases, this can be as much as 7 to 8 degrees Celsius for cities compared to the areas around them that are not built environment. Phoenix actually has an opposite urban heat-island effect. It’s actually not positive. It’s negative, because it’s a desert city, as Mayor Gallego said. And I could see the areas within Phoenix, amazing green spaces and parks and tree cover that Phoenix has clearly put in place to reverse this urban heat-island effects. … There are parts of Phoenix that are cooler than the surrounding areas that are not covered by trees and grassy pastures, but actually desert. And so that’s something that I found quite interesting in looking at Phoenix’s data yesterday.”

Henry Grabar: “Wow, that is really cool. How much of that has to do with the particular surroundings of Phoenix? If Phoenix was surrounded by a hardwood forest, presumably that wouldn’t be the case, right?”

Angel Hsu: “Yeah, exactly. And so for most cities in the United States where it’s not the case and they’re not surrounded by deserts, you see this positive urban heat-island effect where the downtown core is much hotter. And I think we experienced that walking in summertime temperatures during the day in a downtown area, you can almost feel the heat radiating from pavements and from the sides of buildings. So all of that together is really what is the urban heat-island effect. And cities also have this multiplying factor by compounding people into denser environments. Also, we as humans, as we walk along the cities, as we drive our cars, our motorcycles, as we turn our air conditioners, all of that also generates more heat along with a built environment.”

Henry Grabar: “Right. And I have one more question about the urban heat-island effect. How does it compare during the daytime and at nighttime? Is it different? And does it change the way we think about living with heat based on those effects?”

Angel Hsu: “Absolutely. That’s a really great question because scientists and certainly public health experts and policymakers, they want to be paying attention to both. You want to be paying attention to daytime temperatures. When the sun is out, temperatures can get very high. Mayor Gallego talked about these extreme heat waves. So temperatures can easily exceed over 100 degrees during daytime moments. But then nighttime, this is the urban heat-island measure that policymakers and public health officials are increasingly paying attention to, because that’s the time period when our bodies should be recovering from high heat exposure during the day. And so what we’re also seeing is an increasing worrying trend of the nighttime urban heat-island effect also intensifying and increasing due to climate change, and also more and more urbanization. And so that’s really worrisome, whereas the difference between daytime and nighttime urban heat island used to be much wider. Now, we’re seeing that become much narrower.”

Henry Grabar: “Right. So even if the nighttime temperatures aren’t as high as the daytime temperatures, they may in effect be equally or sneakily harmful because that’s the time that people need to recover from the heat they’ve taken in during the day.”

Angel Hsu: “Exactly.”

Henry Grabar: “Let’s turn to Phoenix. I want to talk about the word ‘unlivable.’ Mayor Gallego, you were talking about what the future holds for the ski resorts of New Mexico. But what does the future hold for Phoenix? Are there days when basic civic functions break down or have to be put on hold because it is simply too hot? I’m thinking specifically about images of planes melting into the tarmac at Sky Harbor, but I’m wondering if you have other examples of this.”

Kate Gallego: “Long before I was mayor, we did have a real issue at Phoenix Sky Harbor Airport. When it hit 122 degrees, the ratings for aircraft were not done at that temperature, and so we didn’t have the data about aircraft safety and whether or not they could take off and land safely. They have improved the charts and so we are better adapted. Interestingly, we are just trying at the airport to prepare for extreme temperatures. So for the first time, we believe, in Phoenix’s history, we have also in the last month just invested in equipment to help airplanes that might need to be de-iced, which is not a challenge that we’ve traditionally had, but what we’re seeing is more extreme events on all sides of the climate. So our most recent presidential disaster declaration in my desert city was for flooding. We are getting less precipitation, but it’s coming in more intense events.

“And to key off the last question, what we’re finding is that nature-based solutions can be really important to that. Green landscaping does better than pavement if we have these extreme precipitation events, and it also does better with addressing urban heat island. Phoenix is very proud to have more acres of parks than any other city in the United States, and that is important to us in adapting to climate change. We’re learning from that and trying to bring more and more green space to our city. We have a Cool Corridors Program. We are identifying places where people are likely to be walking or bicycling, and trying to put in more trees and other design factors to make it more walkable and comfortable. Our partners at Arizona State University have helped us come up with several solutions that can make up to a 10-degree difference in our local environment. So we just have learned we have to design our cities with heat at the forefront.”

Henry Grabar: “Yeah. Let’s dig into a couple of those initiatives. Cool corridors, what are those? What does that mean?

Kate Gallego: “We have several different technologies. One is cool pavement where we do a lighter-colored coating on our black asphalt. The cool seal has shown that it’s less likely to absorb heat. Arizona State has found about a 10- to 12-degree difference from that technology. So it’s much more comfortable and people can feel the difference. We originally started with a much lighter coating and now are going towards more of a gray. This particular investment has been very popular with individual neighborhoods that want to be more walkable and comfortable. I do sometimes go around the community and people say, ‘You’re the one who changed the color of the streets.’ It’s sometimes been a subject of a few jokes, but given the amount people are requesting cool pavement, it seems to be increasingly popular. We believe we have the largest program in the world right now for cool pavements. And we started off as a pilot, but because it’s been so popular, we’re doing that more often.

“A bonus we have found with our three years of research so far is that the roads are also less likely to pothole because they’re not having as much temperature change. They last longer. And every mayor enjoys fewer potholes, so that’s been very positive. When we couple it with tree planting along the corridors, then we get a cool corridor.

“So it’s a combination of more modern technology and nature-based solution. And we’re trying to do it with equity in mind. American Forests is a great nonprofit that has helped us be very data-driven. We were the first city in the country to take their Tree Equity pledge, which says that as we plant trees, we will do it with equity in mind. Our wealthier communities in Phoenix tend to have more tree cover than some of our lower-income communities, and we’re being very conscious about changing that. Thanks to a partnership with the Biden Administration, we’ve been able to fund a tree-equity accelerator where residents in low-income areas can get up to four trees. We’re trying to plant them on south- and west-facing walls to reduce the heating of the home as much as possible.

“Cooling is our real challenge here. So if we have trees shading the house, it can reduce your energy bill, which people find very attractive. And then we’re paying people in the community to maintain the trees, so that people get a chance to get more educated about maintaining landscaping and hopefully create more green jobs as we address climate change and heat.”

Henry Grabar: “Yeah, I have to imagine in a climate that can get that hot and is famously dry, that it’s not just about planting trees, right? It’s about taking care of them too.”

Kate Gallego: “We try to plant native species that are drought-tolerant and have good shade. We have beautiful resorts in Phoenix that are very popular that have palm trees, but that is not a focus of this program. We really want native drought-tolerant shade canopies to help cool as much as possible, and they also are very efficient at capturing carbon.”

Henry Grabar: “Of course, palm tree’s famously not very good at providing shade.”

“Dr. Hsu, let’s turn to you. Some of these things that Phoenix is experiencing, how does this compare to what you’re seeing in cities around the world, both in terms of the severity of the heat waves, but also in terms of the adaptations and the way people are dealing with this?”

Angel Hsu: “Well, I just want to say that I think all the efforts Mayor Gallego mentioned are leading in the world. Absolutely in thinking about the intersectionality of how do we actually address this problem of urban heat, climate change and equity, and also carbon sequestration. And so in the policy world, we talk about this in terms of co-benefits. So when you’re planting the trees, you’re not just cooling the urban area, but you’re also sequestering carbon. And so trying to help mitigate the city’s impact on global carbon emissions, which is driving the problem to begin with in terms of extreme heat waves.

“I was one of the lucky scientists contributing to the Intergovernmental Panel on Climate Change, the Sixth Assessment Report, and the conclusions are so clear. Climate change is leading to increased prevalence and probability of heat waves all around the world. And so cities are increasingly facing extreme heat waves. We heard about the European heat dome. I know you lived through that, Henry. We talked about that earlier. And also, China went more than 70 days with temperatures in the triple digits. It was single-handedly one of the worst heat waves that they have experienced in modern history. And we’re just going to be seeing these events happen with more and more regularity. I think just a couple years ago was the first time I heard of the Pacific Northwest in the United States also facing extreme temperatures where many of the homes and the residential buildings lack air conditioning. I have family from there, and it was really terrifying to think about my relatives who are aging also exposed to these extreme heat in very high temperatures.

“So I think that was one comment I wanted to make in what Mayor Gallego said. But yes, we’re seeing in terms of these patterns of inequality, as Mayor Gallego pointed out to Phoenix, where wealthy neighborhoods tend to have the highest tree cover, so people living there have the most access to green space and to that cooling shade. And those trees, as we mentioned, not only provide evaporative cooling and shade, but they also filter out air pollution. And green spaces foster social cohesion. These are all huge co-benefits that people living in those areas enjoy, as opposed to then less wealthy neighborhoods where settlements and residential areas tend to be a lot more dense. They have much less tree cover. And as a result, we’re seeing that they’re exposed to higher levels of air pollution and also higher levels of extreme or higher temperatures and more of this urban heat-island effect.

“And so I think that’s something that’s troublesome. And so we have this index that helps cities gauge how they’re doing on Sustainable Development Goal 11, which sets a goal for cities to be both sustainable and inclusive. We use satellite remote-sensing data to gauge neighborhood by neighborhood how cities are performing on urban heat island, on tree cover, providing people protection from air pollution and giving them access to sustainable transit. And universally what we found — now we have more than 300 cities in this index, including Phoenix — and so what we found is that the majority of cities are burdening poor populations with these environmental burdens of urban heat island and air pollution, et cetera, and even cities that you would think of that come to your mind as being paragons of environmental leadership. Copenhagen is one example. I’m going to pick on them because they do so well on so many of these other indicators. But what we found in our data, they’re burdening poor populations with greater exposure to urban heat. And policymakers in Europe were floored when we shared with them those results. I think it ties back to exactly some of those underlying factors that Mayor Gallego pointed to. We have to be able to identify neighborhoods that are disadvantaged, and then divert resources into interventions like cool pavements, cooling corridors and tree planting. So yeah, we’re seeing these same patterns. Phoenix is not alone. This is something that’s happening in cities across the world.”

Henry Grabar: “Right. And that’s such a typical pattern you see where of course, even though it’s the countries of the First World that are emitting most of the carbon and have historically emitted most of the carbon that is creating the conditions for these extreme heat waves, they also have the most money to adapt. And so it doesn’t surprise me to see that pattern. I wonder, though, are there places with a lower GDP per capita that have rolled out innovations that we in the United States might be able to learn from, or simply have techniques to deal with extreme heat that we could borrow from that might be low-cost or rooted in traditional architecture or neighborhood design or something like that?”

Angel Hsu: “Is that for me or for Mayor Gallego?”

Henry Grabar: “Oh, for you.”

Angel Hsu: “OK.”

Henry Grabar: “If you have any ideas that there’s anything you’ve seen out there.”

Angel Hsu: “Yes. I think it’s tough. I’m trying to think of Global South examples. I was most recently living in Singapore ... It’s on this border between Global South and Global North, however you make these definitions. But it is located in ASEAN, which is a developing region and the GDP is growing very rapidly. And I think they absolutely have a lot of examples that we could learn from in the West, particularly because they’re in a tricky spot of being right at the equator. So even though it’s incredibly green and very lush, every single tree within the Singaporean city and city state is actually tagged with a QR code. So you can go with your phone and then you can scan the QR code and learn all about the tree, the species, and how old it is. It’s quite remarkable. They’re definitely managing every single tree very well.

“I think in working in the space of urban heat island and climate change, I think people tend to say, ‘Oh yes, we should definitely just plant more trees.’ But in a really tropical and humid environment like Singapore, there are actually other trade-offs that tree planting has that people don’t necessarily think about. And so trees, because they are transpiring, they’re releasing more moisture into the air, and so they can actually have the effect of making the air temperature more humid. And because people’s perception of heat, thermal comfort and heat stress relies not just on air temperature, but also humidity, having too many trees in those kinds of conditions could actually make the situation much worse.

“Singapore has done some really creative things with urban design. I remember these amazing malls where they would have wind corridors through them. And so they didn’t actually need to use air conditioning. You could just essentially be in this wind corridor and have this really nice breeze just blowing through the mall. I think there’s a lot of really smart things that can be done with urban design. They’re also looking into building materials that are better insulating for air conditioning, but then don’t absorb as much of the sun’s outdoor radiant temperature. I think that’s really important. And then I think the No. 1 thing for cities, exactly as Mayor Gallego mentioned, is to try to increase the surface albedo, so the reflectance of different surfaces. Not just roadways but also rooftops.

“I had the pleasure — I think this was more than a decade ago — of participating in New York City’s CoolRoofs campaign, where at that time … Mayor Bloomberg set a target for a certain square footage of New York’s rooftop space to be covered with a very reflective latex material. And then studies have just shown that these types of cool roofs can help to reduce 15 percent of the annual air conditioning used in a single-story building and can reduce temperatures by 28 to 36 degrees Fahrenheit within that building. And so I think that’s something that cities can do that would have an immediate impact, because you don’t have to then wait for a long time for trees to actually reach maturity and get that shade cover. You don’t need to hire workers to then go and maintain it. You just paint the rooftop when you have limited space, and then that can automatically have a huge effect.”

Henry Grabar: “Yeah, that sounds huge. So many exciting things to pick up on there. But just with respect to roofs, Mayor Gallego, you talked a little bit about what the city is doing to its corridors and in public space. But what about private property? How do you get your local Walmart or whatever to decide to paint their roof with a special kind of paint that they don’t use on other stores in Illinois or Minnesota or Oregon?”

Kate Gallego: “One innovation that I would recommend to other cities is we’ve created an Office of Heat Response and Mitigation. That’s one place at the City of Phoenix where anyone with a good idea related to heat can go. And any business, nonprofit or homeowner who wants to know more about what technologies reduce heat can also go. We have learned that sharing data about how you can reduce your water bill and energy bill is a very powerful motivator. And the more we can share success stories in that area, the more diverse stakeholders will come on board. There are some companies that are motivated by their commitment to reduce greenhouse gases, but we get a much broader group of stakeholders when we can say, ‘If you design your buildings for the desert, your power bills will be lower and your employees will be more comfortable.’ They’ll also, in my opinion, look better.

“And so we have actually gotten a lot just by making sure people know where to go for good ideas and solutions. Before we created that office, it wasn’t clear who was in charge of heat, and so that effectively made it so that no one was. But now, we have a function within that office that focuses on our built environment. We also have expertise in nature-based solutions, which have been important. Sometimes, we’ve learned that we are the problem. Our building codes don’t allow all of the most innovative roofing materials, or we’re pushing people to pave parking lots in a way that didn’t make sense from an urban heat-island perspective. And just having that expertise that the city has been very helpful to us. We hired a great researcher from Arizona State University who has expertise in heat to run the office, and it’s been wonderful, the number of ideas that our city employees have put forward. People in our fire department know how to adapt to hot conditions, and so we can learn a lot from them.

“We’ve also been able to share what we’ve learned with other cities. So we’ve consulted with cities ranging from Portland to London on how we’ve learned to adapt to the heat. Hot summers happen every year to us, but we were able to provide some useful advice to the fire department in London which was dealing with heat conditions that are very unusual for them. And many other cities are now creating offices focused on heat. Phoenix was the first to have ours as a permanent part of government in the United States, but Athens has a very innovative office. Freetown in Sierra Leone has a good one. They were actually doing tree planting with local workforce before we were, so we learned from Global South communities about programs that make sense.

“One of the wonderful things about mayors and cities is that we’re willing to collaborate, we’re willing to share ideas and we learn from each other. That’s part of the reason I’m optimistic that cities will really lead the way on keeping 1.5 alive and really addressing global climate change challenges. There are many national governments that are not meeting their climate change goals, but communities within those national governments that have stepped up and led.”

Henry Grabar: “Yeah, that makes a lot of sense. Even looking further out in the future, are there big-picture changes you envision for Phoenix? I mean, 40, 50 years down the road, are we talking about a city that will be unrecognizable to people who live here today, or it’s a matter of more incremental changes?”

Kate Gallego: “I’m hopeful that a lot of the big solutions to climate change will come out of Phoenix. For some cities, they refer to it as a problem that they will face in the future. Climate change is a problem right now for us, and that creates urgency that spurs innovation. We’ve had many private-sector companies that have come up with good ideas for technology that address heat and climate change, and we hope to be able to share that with other communities and really be part of the solution. We are sunny more than 300 days a year, and that gives us a great climate to make sure that solar is integrated in building products and that we can share those with other communities.

“We have, really, sustainability in many of our larger corporate sponsors. I would guess my city is the only city where an NBA arena is named after a company whose brand is sustainability. In our case, it’s a company called Footprint, which is trying to disrupt disposable utensils and put sustainability at the forefront of that product design. So I hope that we’ll take a negative and turn it into solutions that will help Phoenix be more comfortable, both adapt and mitigate climate change. We have the real reason and the push to be part of the solution here.”

Henry Grabar: “Right. Speaking of climate change technology, Dr. Hsu, I want to ask you about air conditioning. Indispensable technology of the hotter future or causing as many problems as it solves?

Angel Hsu: “That’s a million-dollar question. I think what’s clear from the climate change scenarios and already globally, the world has experienced temperatures 1.1 degrees Celsius higher on average than pre-industrial levels. And that trend, if exactly as Mayor Gallego said, we know that national governments are failing. New York Times, the front page talks about how only 26 countries have actually submitted increased ambition, climate change plans ahead of the climate negotiations which will take place in Egypt. I’ll be there for the first week. And so that’s really worrisome, because if we continue on this path, if we look at what national governments have pledged, we’re headed towards a 3.6-degree median warming world by 2100. And so the baseline conditions, and that just also feeds the possibility and the probability of these extreme heat events and will make many cities around the world become, frankly, as you said earlier, unlivable.

“And so that will certainly necessitate, and a lot of these models do anticipate an increase in air conditioning use, particularly amongst Global South cities and areas that are facing disproportionately the brunt of climate change and global warming. And so yeah, that’s absolutely going to be a huge part of the picture.

“I think the key is, can we think about making those air conditioners more efficient? Can we actually shift electricity grids away from fossil fuels that are just intensifying the problem and leading to more of these intensified positive feedback loops and source them, empower them through renewable energy such as wind and solar? And so I think that’s also really key. I don’t think that air conditioning necessarily will be a huge problem. If we’re actually powering them with renewable electricity sources, we can make those technologies a lot more efficient. And then I think in the ways that buildings are designed, we’ve talked about building materials, and there’s certainly building materials that you can use that are less absorptive and less absorbing than others.

“I grew up in a brick house in Greer, South Carolina, for example, and I just remember dying in the summer times because my parents did not believe in air conditioning, and so we just suffered. And at nighttime, I couldn’t even sleep in my bed. I was sleeping on the floor because it was actually cooler. But yeah, absolutely there’s going to be increased need for air conditioning as an adaptation mechanism. But I think the critical piece is, can we actually make that more efficient and can we power those air conditioners through renewable energy?”

Henry Grabar: “Right. The thing you hear about air conditioning in Europe, which has been very slow to adopt air conditioning even as summer heat waves become more and more of a regular occurrence, is the concern that if everyone in a city has air conditioning, it actually would raise the ambient temperature outside to a degree that while might protect people inside, would leave them more exposed outside. Is that a concern?”

Angel Hsu: “Yes, absolutely. As I mentioned … one of the drivers of the urban heat-island effect is certainly air conditioning. Because in order to generate cooler air indoors, it’s got to generate heat. It’s got motors and fans that are running, and all of that movement generates heat. And so that’s one of the reasons why I mentioned we absolutely need to be rethinking how we cool buildings and homes in the future. And this is a very ripe area of development. And so yeah, as more people are demanding air conditioning or need it simply because temperatures become dangerously high and more extreme, that’s something that we need a lot more research and development on.”

Henry Grabar: “Yeah. Let’s turn to the building question maybe to you, Mayor Gallego. You’re in charge of — maybe not you personally, hopefully not you personally, but Phoenix has a building code, presumably. Are there elements in there that are designed to make sure that builders are building with the climate in mind? Obviously, we have this sort of idea of what kind of vernacular Southwestern architecture looks like, but we also know that Phoenix and every other city has a lot of glass wall skyscrapers that presumably let in a lot of sunshine and a lot of heat all day. So I’m wondering if you think that the building code is a place where you can push people to build in a way that ultimately keeps residents and workers cooler and safer as those buildings reach completion and as the city goes forward into the future?”

Kate Gallego: “Building standards are very important. We believe it’s important for communities like Phoenix to participate in code development because sometimes, codes are written with cold weather communities in mind. And so that will push buildings to be built with the big challenge being heat in winter, and that really creates some negative impacts on sustainability in Phoenix and doesn’t make sense. So we try to work hard to make sure that building professionals nationally understand what to them may be a little bit of unique challenges we have in the Southwest. My peer mayors in the Southeast have similar challenges, although they have more humidity like Singapore at the forefront of their design.

“We’ve actually found that sometimes, the building codes though limit the ability to innovate. We’ve had many cases where we’ve pushed people towards what we thought were energy-efficiency improvements, but that took away the ability to try more natural building materials or nature-based solutions. So I guess from my perspective, there’s some baseline code changes that are important, but we also need to allow very, very smart design professionals to try new things and come up with new solutions.

“Summer cooling bills can be quite high in Phoenix, and that’s very powerful motivation for individual residents and for design professionals to address these challenges. When residents are going from house to house and trying to decide which one to buy, if you are cooler and more comfortable in the summer and you don’t hear the air conditioning overwhelming, that is a powerful selling point as well. So for us, it’s a mix of codes, educating residents, educating design professionals, but also getting out of the way when we have creative solutions.”

Henry Grabar: “Got it. And then when it comes to the most maybe short-term thing, which is to say the days in the summer where you look at the forecast and you see that the next three days are going to be over 110 degrees, what’s the playbook for you? What do you do as a mayor to make sure not only that people can get the help that they need if they’re in a vulnerable situation, but also to protect workers? Because people who are assigned to, say, working on a job site or working outside on one of the hottest days of the year, they may not be able to tell their boss, ‘It’s too hot today for work.’ So what do you do as a mayor to make sure that people tasked with working outside are able to make it through these events in one piece?”

Kate Gallego: “In terms of vulnerable populations, one policy choice that we’ve made here that I’d recommend to other communities is setting up cooling centers, a place where people can go for relief. We have 50 locations throughout the city, and we try to distribute maps in very creative ways to reach the people who need to know where those are located. We also have really focused on making sure we get water out to our community. We started with plastic bottles and have now moved towards aluminum, which we find as sustainability benefits get reused more often and stay cool a little bit longer. The cooling center network has been important.

“We got great advice that we needed to create a program called Cool Callers where we can check on people who are the most vulnerable during heat waves. Right now, that is a voluntary program, but many family members have a sense Mom or Grandma might be really vulnerable in a heat wave. And so can we just make sure people know that there are resources out there and have a chance to get support? And we can couple that with weatherization, trying to upgrade the homes that are most vulnerable in a heat wave. We know that our most serious health consequences for people who are indoor during heat waves and have real challenges are in buildings that either don’t have functional cooling or don’t have any cooling. So again, how do we make sure we support those who are most vulnerable?

“Every single year we do something differently. We continuously are learning. That is same with the role as an employer. For example, we looked at data of city employees who experienced heat stress, and found that firefighters doing mountain rescues in the summer were very, very prone to being hospitalized for conditions related to heat. And we’ve made changes so that when it gets above a certain temperature where we have a heat event declared, our most dangerous park trails, we close down so that our firefighters don’t have to go out and do rescues. And that has been very helpful in reducing those heat-related stress events.

“It is not perfect. We had a reality TV show that illegally went out in the middle of a heat event and had to be rescued. We hope it was a teachable moment and trying to make sure they don’t get unfair, positive free media off of doing something that puts our city employees at risk. But we are trying to be data-driven and looking where we can make the biggest changes to make sure our city employees are safe. And we work with private-sector partners as well to both share best practices and learn from them.”

Henry Grabar: “Right. That’s fascinating. We won’t give any free publicity to the reality show, but shame on them. And that’s very interesting. We sometimes people think that a hot day is a good time to go outside, but it sounds like in Phoenix, that is not necessarily the case.

“It is almost time for audience questions. But first, if you’re enjoying this event and you want to join future events of this kind, please be sure to sign up for the Future Tense and Knowable newsletters and follow them on Facebook and Twitter. The next event in this series will be on climate finance, and the Knowable crew will share registration details about that soon. And now I’m going to turn it over to Emily for questions.”

Emily Underwood: “Thank you so much. This has just been fascinating, so many good ideas. Just a reminder to our audience, that you have a lot of power to share these ideas out. So send them to your colleagues and your family, and we’ll have a video of the event that you can share and a transcript.

“So we just made the decision that I should ask these great audience questions because Henry has so much expertise around many of these topics from his reporting and the book that he has not yet published. Sorry about that mistake earlier. But I would like to start with a question from Giovani Palafox-Alcantar. He asks, ‘What is the major trade-off when trying to create more green areas in cities? Is it watering the areas versus the temperature that might help to cool down? Is it the urban space and construction cost? What are you balancing as you try to make these choices?’ Mayor Gallego, can you take that one to begin with?”

Kate Gallego: “Part of it is political. We have to convince our community that this is a priority. I am lucky in that the voters of Phoenix have now voted several times to set aside a portion of our sales tax just for our parks and green spaces, but we constantly have to remind people why they’re important. It happens more often than you think, that someone will approach me and say, ‘That park is not being used enough. We want you to sell it to us and it will help you balance your budget.’ And I have always said, ‘No, that is not our priority in this city.’ But there are some stakeholders who don’t share my vision.

“... The workforce has been a challenge lately. We’ve invested in an apprenticeship program to make sure we have the parks and landscaping professionals to support our landscaping. We’ve had some pretty significant storms where we lost a lot of trees. And so we know that we need to make sure we have best practices in pruning the trees and just maintaining them so that they are as resilient as possible, but also replanting. That is sometimes a challenge on the workforce side. We generally feel there are not as many young people going into careers in this area, and so we’ve also invested in an apprenticeship program on more edible agriculture and supporting food-based programs as well, because we think this is an important profession for the future of our city. And so we want to support a great workforce and make sure people know that there’s a career path and that you can be an accomplished professional going into these areas. That’s been a bigger challenge more recently, but one that is top of mind for us right now.”

Emily Underwood: “Dr. Hsu, in addition to the political trade-offs, are there other types of trade-offs that cities around the world have been contending with?”

Angel Hsu: “Yeah. I think that Mayor Gallego provided a really great overview, and I agree with everything that she said. I think politically and getting people behind these policies and these interventions is really important. I’m also thinking back to Singapore, and there’s just a huge space constraint. I think it’s just physical limitations of a city state that’s as dense as Singapore. And so what they’ve done in terms of their planning and zoning policies is anytime there’s a new development that’s being proposed, and many cities also in North America have these types of environmental impact assessments that have to be put in place before a developer can actually follow through on a project. But in Singapore, it is the same. And they have to actually provide provisions for how they’re going to replace the green space, the greenery, the tree cover that could be displaced as a result of a building development or something else. And so I think that’s something that’s quite interesting.

“And of course, I mentioned that tree planting takes time. And so if a mayor or a policymaker, an urban planner, is thinking about trees simply to reduce the urban heat-island effect, that can certainly take time. And so there are certainly other types of measures that can be put in place to have a more immediate effect. As we discussed, some of this very reflective coating on roadways or on building rooftops.”

Emily Underwood: “One of our questions is about pavement, changing the materials or coating them with something. So Donald Samuel asks, ‘Instead of traditional cement or pavement, are there better composites which can be used for paving which are more ecologically friendly? For example, are porous pavement-like surfaces a cooler material?’ Henry, I know you’ve been thinking a lot about pavements, so do you want to jump on that first? And then we’ll have Dr. Hsu and Mayor Gallego add on?

Henry Grabar: “Well, gosh, it’s a little embarrassing, but I don’t actually know what the top reflective pavement surface is off the top of my head. I think you might want to talk to Mayor Gallego’s office about that. Obviously, porous pavement is a good thing. I think if you can reduce the amount of pavement, period, and turn any part of that into something that’s either green or just use it for another use entirely that might otherwise expand the city’s footprint, that’s good news.

“The other obvious benefit of porous pavement is for flood events because it’s funny, how just like Mayor Gallego was saying, that they’ve been dealing in Phoenix with not as you would expect, with drought, but also with flood events. That’s another one of these extreme weather events that comes along. And some of the changes that we can make to deal with heat, I think, are also productive for dealing with flooding. And massive expanses of blacktop are a huge generator of flooding because runoff lands on them and just goes somewhere else. So trying to find a way to turn all that pavement into something a little more absorbent would certainly be good for dealing with that, and I’m sure is good for dealing with the heat as well.”

Emily Underwood: “Sorry to put you on the spot, Henry, but that was a great answer. And Henry, maybe I should let you ask Mayor Gallego and Dr. Hsu about pavement. Do you have any burning pavement parking lot questions you’d like them to answer?”

Henry Grabar: “Well, I guess I’d like to know from Mayor Gallego if Phoenix has parking minimums, which require a certain amount of parking come with every use. For example, if you wanted to open a restaurant, you’d have to include one space for every 100 square feet of restaurant space. If you wanted to build an apartment, you’d have to have one space with every apartment. And obviously, all that parking that gets created as a result of those requirements both takes up physical space in the city, which contributes to the heat-island effect, and also encourages driving, which creates carbon emissions, which ultimately makes this problem worse. So does Phoenix still have those policies?”

Kate Gallego: “We have been really trying hard to reduce impediments to more transit-oriented city, and particularly looking along our bus and light-rail corridors, so that is our transit system. We don’t have a subway in Phoenix. We find with multi-family residential, the biggest minimum requirements on parking have come from the financial partners. So apartment developers tell us our financial partners demand a certain parking ratio for units. But there’s an exciting development in the Phoenix metro area called cul-de-sac that has gotten, I think, international attention. ... So they got all of their I’s dotted to build a multi-family community where everyone agreed not to have a car. And so they really designed the community around a transit-focused lifestyle. It has been very successful financially, and we are trying to lift that up as an example of what is possible. And we’ve had people come, particularly from Europe, that are interested in financing more projects like that. So I’m optimistic we’re about to be on a breakthrough point.

“I guess I don’t want to say that everyone in Phoenix agrees on lower parking minimums. We do have some stakeholders who really hate when people park on their property. And so when we discuss parking minimums in Phoenix, it is a robust conversation and there are definitely people on both sides of the issue. So it’s still a public-policy debate, but we’re seeing some very positive steps forward.”

Emily Underwood: “So Mayor Gallego, I want to follow up with another really hot-button issue in Phoenix, which is water. We have had a number of questions from the audience, Mike Stanley among them. ‘What about the use of water in green spaces? Are we going to run out of water to maintain these?’ And, ‘What is the interplay between temperature mitigation and water consumption?’ That was from somebody else.

Kate Gallego: “I feel very strongly that investing in trees makes sense from a sustainability perspective. When you consider all of the inputs, including water, it is important that they be drought-tolerant species. And there is some water used, but I think if you look at our climate overall and the contributions that trees can make to both mitigation and adaptation around climate change, it makes sense to me. We are particularly focused on reducing industrial water use and large-scale cooling. Our Phoenix Sky Harbor Airport did a program that was very important for our community in showing how you could reduce water use related to cooling, save money on your energy bill and your water bill. And there was just some really important technology in that area that we hope to spread to more of the private sector using our very successful project as an example. And so we’ve partnered with Bonneville Environmental Foundation and others to create a blue bank to help finance these projects. And we’re very open to providing technical support or whatever in addition to financial support. We’ll help make a difference in that area.

“And then we are looking at high-water-use landscaping and other areas where we think we can make a difference. I’ve joined a coalition called the 50L Coalition, which is named after the 50 leaders that the average resident of Cape Town in South Africa used when they had their very extreme drought event. And that coalition includes partners from IKEA to Procter & Gamble who are coming up with better technologies that reduce water use throughout the design process and when devices are in the home. I’ve been very pleased to learn from that, that most of us spend too much time pre-washing our dishes before going in the dishwasher. So hopefully there’s one nugget of news you can use to reduce your own water consumption and maybe make life a little bit easier.”

Emily Underwood: “Thank you. Speaking of news you can use and the individual experience of this, we’ve had a couple audience questions, including from Chirag Jay Patel about, ‘What can individuals do to reduce heat stress and to stay safe?’ Dr. Hsu, you want to start with that? I’d love to hear from all three of you.”

Angel Hsu: “Yeah, I think that’s a great question. And actually, I did want to talk about pavement. If I could just talk about pavement.”

Emily Underwood: “Of course.”

Angel Hsu: “So one model from the Global South that I think is quite interesting in terms of alternatives to just concrete or asphalt, and then this also I think addresses what Mayor Gallego was saying in terms of conserving water, China has a program to develop sponge cities. So they have, I think, a dozen or so efforts in cities all around China to design cities to actually hold on and to retain water and precipitation a lot better, so that you don’t have as much runoff with these very impervious services that can also drag urban pollution into farmlands and agricultural areas, but then can also help to retain water and also address potential flooding events. So I think that the sponge city concept could be one potential answer, and then maybe Phoenix could be a cool and a spongy city. So that might be something to think about for the next environmental campaign.

“In terms of individuals, I think number one is just to educate yourself and to become aware of the dangers of extreme heat. I often refer to extreme heat or just high temperatures as a silent environmental killer. And this is the reason in the 2003 European heat wave so many people died from that event because people just simply were not aware that heat can actually be a very serious human health issue. And so they didn’t realize that with high temperatures, if they were feeling dizzy or dehydrated, they didn’t understand what the warning signs or the symptoms of heat stroke were. And simply it became too late. And even the foreign minister in France was on vacation. He was in the French Riviera, and didn’t think that this was a health emergency before it was too late. And so now they’ve gone back and they’ve done studies to show that the actual death toll of the European heat wave is several times higher than what they initially registered simply because people were not aware. So I think that’s the number-one thing that people can do is just become aware.

“And I think, Mayor Gallego, these maps of cooling centers, that’s really important. And we’re certainly doing some work. Actually, when you mentioned the first officer of heat mitigation and response, we’ve actually had conversations with David Hondula on research to how we can make that information more accessible for people, to their smartphones and integrated with alert systems so that when it’s a really hot day, then they can, based on their geolocation, they can find a cooling center or a mall or a library or someplace that they can go to seek relief, and particularly if they’re part of these vulnerable populations. So number one, I would say, is to get informed.”

Kate Gallego: “I will echo that as well. I think the more you can check on people who might be vulnerable during heat events, if you have people in your own life, maybe start there, but also just volunteering and supporting. Older adults can be vulnerable. People who have unstable housing situations, including no cooling at home. So volunteer opportunities in that area. We are trying to do more with our employees and making sure we have sensors and analytics. We’re also trying to design communities better. And I understand there are many design professionals who are part of this conversation, so we would love to get your innovations. We are redeveloping our largest public housing community in the City of Phoenix, and we’re putting heat at the forefront as we design that. So we had existing obsolete units and we took a lot of heat-related measurements and then are trying to design with airflow, cooling, creating more shaded places for outdoor recreation. And so if you are a design professional, you probably can help contribute in that area where we think there’s still a lot of room for innovation.

“We’re also hoping people in the technological world can step up and help us with, are there better devices that can help address heat-vulnerable individuals? We have incredibly detailed devices that can manage your home energy consumption via your thermostat, but is there a way to support those who are most vulnerable with technology as well? So throwing out some ideas there.”

Emily Underwood: “Thanks so much. We are almost out of time, but I want to give Henry a chance to ask one last question if there’s something that’s on your mind or that you want to wrap up with.”

Henry Grabar: “Well, I do want to say one thing about trade-offs, because I think that one of the major questions looming is how this heat resiliency gets taken into the kind of structures that we’re building. And while in Phoenix, the prospect of huge electricity bills may be a sufficient motivator to get people to design things in a way that keeps apartments cool, I do wonder if that’s going to be the case in other places. I know that in the UK, they now have a legally recognized category for multi-family apartments that is cross-ventilated, which is to say windows on both sides just to make sure that people can get a breeze in there. Obviously, that’s going to make the cost of housing go up. That seems to me like a major trade-off that’s going to come across in the next couple decades. And I just wanted to mention that quickly in response to the earlier question.

“I think my final question is for the mayor, and it’s whether if you want to try and market Phoenix as a cool and spongy place, and what the tourism department is going to think about that.”

Kate Gallego: “Our Economic Development Department sometimes uses the slogan, ‘Phoenix is hot,’ which is referring to some of the semiconductor investments and advanced bio-investments. So it’s sometimes a little bit tongue in cheek in embracing our climate. We have gotten international attention for some of our cool corridor work, and I think that is powerful and important. People look to us to lead on sustainability because we do live in a climate that is at one extreme of the city world. And I think for people to want to be part of our community, they value sustainability a lot. So I do hope it is part of our brand. I’m not sold on the word ‘spongy’ yet, but I’ll let that sink in a little bit and think about that area.

“But I have an environmental degree and I think that helped me win the election for mayor, because people value sustainability in Phoenix and they want elected officials, business leaders, nonprofit leaders to do the same. So I hope it will be part of our brand, but I’ll let the marketing folks help us with the exact language we should use.”

Emily Underwood: “Thank you so much. And thank you, Mayor Gallego, Dr. Hsu. And Henry, you just did such a lovely job moderating this. Really appreciate it. That’s it. As I mentioned before, we have another event on climate finance coming up and we’ll be posting details about that soon. Thanks to everybody who joined in and posted such great questions today and really participated. We’ll be posting this and additional resources where you can dig in and maybe get some answers to the great questions that you asked after the event. And we will see you next time. So I just want to say thank you again, and I hope everybody will join us for our next event.”

Angel Hsu: “Thank you.”

Kate Gallego: “Thank you.”

Henry Grabar: “Thanks.”