This episode is part of our Overheated series, a collaboration between What on Earth, Quirks & Quarks, and White Coat, Black Art, that explores how heat is affecting our health, our cities and our ecosystems.

Below is a transcript of the episode.

BOB MCDONALD: I'm Bob McDonald and welcome to a new season of Quirks & Quarks, and a special program we're calling "Overheated."

Not to repeat ourselves … but it's what's been happening these days. We're breaking heat records, again and again.

Globally, average temperatures are rising. July 2024 was the warmest July on record for the entire planet according to the US National Oceanic and Atmospheric Administration. And we've now had 15 consecutive record-shattering months when it comes to high temperatures.

And where we're feeling it most is where most of us live: cities are particular "hot" spots, thanks to how they're built - and what they're made of.

Researchers are trying to understand exactly how our urban environments are amplifying and concentrating heat.

It's an area of research that's only growing in importance as more and more of the global population is settling into cities - and as our planet heats up around us.

Understanding how it is changing our bodies and our living spaces is a matter of life and death.

Researchers are also learning how to re-work cities. Transforming them from being part of the problem, to part of the solution.

Today, on a special edition of our program, we're unpacking the science behind sweltering heat in cities - and looking at how to cool down our concrete jungles.

This is Overheated - a Quirks and Quarks special.

BOB MCDONALD: We start today in Canada's second largest city – and an unusual platform for scientific research.

So have you had any reactions from people as you ride this weird looking thing around the city?

JOHANNA ARNET: Yes, I have. I've been asked if I'm spying. I've been asked if I'm NASA. A lot of people are really curious and friendly. They do approach me and ask what it is. I tell them exactly how I explained it to you. It's the temperature bike, I'm just measuring air temperature and not listening to anyone (laughs).

BM: I'm here in downtown Montreal with Johanna Arnet, she's a master's student in Urban Ecology at Concordia University. She's part of a growing field – scientists investigating how a city's structures can affect the temperatures we feel.

To get as much detail as possible, she's transformed her bicycle into a portable temperature sensor.

Interesting looking bike you have here. I notice that it has a bell on the front, yes, but there's all kinds of other bells and whistles on the back. What's going on?

JA: There are, yeah. So this is a mobile temperature sensor for our study on urban heat islands and the interurban variations in temperature.

BM: OK, now I noticed that it's got a white thing on the top of a tower here you've got this triangular tower. It looks like a bunch of saucers that have been piled up. What's that?

JA: Yes, yes. Well, inside these saucer looking things is a temperature probe measuring the ambient air temperature. OK, it's mounted at a meter 50, which is more realistic for human comfort.

BM: It's about eye level to me.

JA: Yeah, exactly. And then there's a white cylinder halfway down here, what's that? That's an infrared radiometer, which is for surface temperature. So it's measuring the temperature of the surface behind the bike.

BM: Oh it's looking down at the ground. And then we got a green box with Garmin written on the top of it?

JA: Yes. So the garmin is the GPS to put all the data together, localize it for spatial analysis, and inside the box is all the wires, the data logger, the battery.

BM: So how do you actually use this when you're measuring temperatures?

JA: I have 5 routes planned around the city that I bike multiple times during the day, the hottest part of the day, as well as during the night, 3 hours after sunset. This takes a measurement every one second, which ends up being every couple of meters depending on how fast you're biking. For every point I have all this data, air temperature, surface temperature, the solar radiation.

BM: Ok, is this on right now? Yes, it is. It is. So can I collect some data? Can I go for a ride and actually collect some real data in Montreal? Yes please!

Oh, goody. I'm part of a scientific project. This is great. I feel like a real scientist here. Here we go. Boy, it's a little shaky on the steering with all the weight on the back!

I take off, down a side street, and then merge onto a busy road.

Am I allowed to ride here? Well I'll ride here anyway.

It's a familiar picture in cities in Canada. Asphalt on the road, concrete sidewalks, and glass buildings towering above me. Then I get to a park, and I instantly feel the difference. Under the trees it does feel cooler!

More than half the world's population lives in cities. And that's expected to rise to 70 per cent by the year 2050. Here in Canada, more than 80 per cent of us live in an urban environment.

That's not just including the big metropolises like Toronto, Vancouver, and Montreal, but also the smaller municipalities across the country, like East Gwillimbury, Ontario whose population, according to Stats Can, has increased 44 per cent in just 5 years.

People look at you very strangely as you're riding around on this thing. It's very strange, I'm sure. Yeah, like you're some kind of alien invader or something like that. That was fun.

Johanna works in the lab of Dr. Carly Ziter. She's an urban ecologist and an associate professor at Concordia University.

Hello and thanks for letting me ride your bike!

CARLY ZITER: You're very welcome. Glad you enjoyed it.

BM: Why are you researchers using bicycles to map out hotspots in Montreal?

CZ: So urban heat is a huge challenge for today's cities, and we know it's going to become more of a challenge with climate change. Now, many studies have focused on differences, you know, between the city as a whole and surrounding areas, But we know that temperature can really vary hugely within the city itself. You know, a green leafy neighborhood might be several degrees cooler than a dense neighborhood. Lots of buildings, low tree cover. So a bike lets us be really agile in terms of our measurements, get, you know, in and out of small spaces within the city to really understand air temperature at the kinds of scales where people live and work and play.

BM: But why a bicycle? Can't we get information from satellites?

CZ: We absolutely can, and that information is really helpful. But what satellites are measuring is the surface temperature, and that's a little bit different than what we actually feel. So what we're trying to do is understand air temperatures so closer to what people feel, closer to the kinds of temperatures that might, you know, make us uncomfortable, make us sick. And so a bike gives us an additional layer of information because we have that air temperature. And it also lets us go out in different times of the day. A satellite might only pass at a very particular time. And we know that the impacts of heat can be really different depending on when we're measuring it.

BM: But why is urban heat important to study in such fine detail?

CZ: One of the reasons we want to understand urban heat in fine detail is because those are the kinds of of scales that people can really make a difference. So often when we're trying to mitigate urban heat, when we're trying to reduce urban heat, we're focusing on interventions like tree planting, like changing the vegetation at a fine scale. And without understanding the impact of those actions, it's really hard to improve them. So understanding the fine scale pattern lets us understand how we can intervene, you know, as individuals, as city decision makers. One of the things Johanna is trying to understand now is in these dense neighborhoods, how much of a difference can we make by adding, you know, a few trees here and there? So an even smaller intervention. And that's something we don't have as good of a handle on yet.

BM: Out on the streets of Montreal, Johanna Arnet and I go through the data from my bike ride.

So show me some of your data points here along this route.

JA: Yeah. So between here where you can see it's dark blue, that is 28.79°, it's a hot day. And then here it was 30.88.

BM: Wow, and that's only a few blocks away. What's the difference between the ground temperature and the air temperature?

JA: Yeah. There's a lot more variation from even like a few meters to another. The interesting part is how much hotter the surface can be than the air. So for example here the air temperature was 30.66° and then the surface temperature was 47.38.

BM: Two degrees air temperature might not sound like much, but as Johanna's colleague Bella Richmond, a PhD student in Dr. Ziter's lab explains, it actually makes a huge difference to how the human body reacts.

BELLA RICHMOND: I think, like when we think about what we notice and what we feel when we walk from a street that has a lot of canopy cover, a lot of trees where, you can tell when, in summer, everyone's on the same side of the street because that's where all the shade is, because we're naturally drawn to that. But then, when you walk to the next block where there's no street cover or very little, you can instantly feel that effect. And that air temperature difference might be 3-4 degrees, but you're, you're sweating, you're thirsty, you're looking for a cafe to get an ice coffee. These are the things that's happening with only a few degrees difference, which is, to the human body, a huge temperature difference.

BM: This isn't just a problem for southern cities - it is affecting cities across the country – in the North as well. Another person trying to study this is University of Alberta urban planner Dr. Sandeep Agrawal.

SANDEEP AGRAWAL: Cities are hotter in general, wherever they may be. And the question that popped in our head was, is Urban Heat Island an effect here within the city of Edmonton?

BM: Unsurprisingly, he found that even a city like Edmonton was still much warmer than the green spaces around it. His research is showing that urban heat can affect any built up environment where concrete is king.

SA: In Edmonton, we found that urban heat island effect was quite prominent, especially during the summertime. In some parts of the city, we saw an increase of temperature up to six to 12 degrees compared to the rural surroundings.

BM: He extended his research to other parts of Canada's north - and sure enough, the urban heat effect was showing up there, too.

SA: We have looked at Yellowknife and large parts of Northwest Territories in general. And we do find higher temperatures in some of these small urban communities across the Northwest territories. It's partly because of the rise in temperature globally, which is affecting the northern part of Canada much more, along with the surfaces, the types of surfaces being used in the communities, asphalt and concrete.

BM: The urban heat effect exists because of a complicated mix of physics and environmental science. Dr. James Voogt has been studying these factors for more than 30 years. He's a professor in the department of geography and environment at Western University.

Hello and welcome!

JAMES VOOGT: Thanks for having me.

BM: Now, you've been researching urban heat for a long time. Why is it so interesting to you?

JV: I think urban heat is one of the important microclimates that affect a lot of people. And with the urban population now being the majority of the world's population, trying to understand the climate of cities is really important. And heat is one of the basic elements of climate.

BM: Now, when you say microclimates, what do you mean by that?

JV: We mean the the very small scale from meters up to, say, hundreds of meters of the atmospheric parameters that are in cities, so anything that we consider to be climate we can look at on very small scales and the variability of structure and materials and the built environment in cities creates a lot of different microclimates in close proximity to one another.

BM: So that's what you feel when you say, step into a sunny area, then into a park, you feel the temperature difference, that kind of thing.

JV: That's exactly right.

BM: Well, take me through what we know about why the urban heat effect even exists.

JV: So the story with urban heat starts with the changes to the cover, the materials that we have in cities, so you typically are replacing natural materials with built materials and those built materials have different properties, what we would like to call the urban fabric. Those materials that we put into cities typically are a bit better at absorbing sunlight and they're often quite a bit better at storing heat. And then as part of building cities, we're also changing the three-dimensional form of the surface, so we go from something that's typically more flat and homogeneous to something that's got a lot more 3 dimensionality to it.

So we increase the total active area that can absorb radiation. We create this geometry that allows sunlight to be trapped between buildings and it also reduces the loss of radiation heat at night. And the third thing we do is we add heat to that atmosphere. So through our use of energy, through transportation, through heating and cooling our buildings, we're adding a source of heat to the city.

BM: Well, those micro climates in the cities then how do they affect the overall climate of the air passing over the city from the countryside?

JV: Yeah. So what happens at the surface does get passed up to what we would call the urban boundary layer. So there is a warming of a layer up to a kilometer, maybe even two kilometers on a nice sunny day upwards into the atmosphere that's transferred by the winds downwind. So there is a plume of warmer air that extends downwind from a city.

BM: Is it the buildings themselves? Is it the way they're built that makes a difference, or how we arrange them In the city?

JV: It would be both the height of your building compared to the spacing. Especially when we think about across the street to the height of the building over there. That height to width ratio is very strongly related to how warm that neighborhood will be at night.

BM: Well, how does that make things hotter?

JV: Slows down the rate at which the surface cools. So essentially what we're doing is we are obstructing the view of the sky for those surfaces in what we call the street canyon. And as we push the buildings in closer and closer together, we see less and less of the sky.

BM: OK, so the heat stays on the surface rather than radiating out into space.

JV: That's right. Yeah, the process is happening. It's just happening much slower when the height to width ratio is large.

BM: As cities grow around the world, some are expanding upwards with taller buildings, but others are expanding outwards with urban sprawl. How do those two factors come into it?

JV: Yeah, so densification is going to always lead to having a bigger night time heat island from that process we just talked about. It would have other microclimate effects too. So as you go upwards and you densify, you're going to have impacts on air flow. You're going to restrict air flow. You're probably going to reduce pollution dispersion to some extent. By day you would have more shading. So certainly downtown Toronto, for example, right down in the heart of the central business district, you get shading by all those really tall buildings. It's actually cooler for a few hours in the morning than it would be in other parts of the city. But then it, the opposite effect occurs at night, so you can have a stronger heat island.

BM: Now what about urban sprawl?

JV: Yeah. So as you spread out, you're going to reduce the heat island of those particular neighborhoods and you have perhaps more opportunity to build in vegetation, but it does come with the consequence of being much less energy efficient. So a sprawling city is not efficient in terms of greenhouse gas emissions. If we're expanding with a lot of sprawl, it's also going to create typically more surfaces that we will see as being hotter by day because you have typically have more roads and you more have more impervious surfaces.

BM: Now, changing the city is not easy. Are you actually seeing progress in cities? Do you see more cities adopting these tools to help combat the severity of these urban heat island effects?

JV: I do I, I think there is pretty widespread recognition that urban heat islands are something to be concerned about that has grown because I think there's good recognition or increasing recognition that heat is a public health concern. So if you look at all of the environmental factors, I like to call them the ways that weather can kill you, heat is number one. Microclimate is important in thinking about how we're feeling in these cities, and that becomes important for our health as we go forward.

BM: Dr. Voogt, thank you so much for your time.

JV: Oh, you're very welcome.

Dr. James Voogt is a professor in the department of geography and environment at Western University.

BOB MCDONALD: I'm Bob McDonald and you're listening to a special edition of Quirks & Quarks: Overheated – where we're exploring the risks of urban heat – and what we can do about it.

Heat is more than uncomfortable. In North America heat kills more people than any other weather event. Heat tends to affect the elderly, children, people with disabilities, renters, and those suffering from mental health problems the most.

A recent study reported that Europe saw 47,000 heat-related deaths in 2023, and that number is expected to triple by the end of the century. In that same year the United states recorded the most heat waves since 1936, and as such doubled its average heat deaths last year. Here in Canada, Quebec recently reported that on average, heat kills 470 people and leads to 36,000 emergency room visits every year.

All of these numbers are expected to get worse as the planet gets hotter.

And if heat doesn't kill you, it can affect the body in many ways.

There are links between high temperatures and cognitive dysfunction and worsening mental health conditions. It can put a strain on the heart by making it work harder, leading to heart disease. The kidneys, lungs and skin, all are affected by extreme heat.

We're not the only CBC Radio program looking at heat right now. White Coat, Black Art is also exploring the theme of "Overheated", looking at how scientists are investigating the effects of heat on the human body. Dr. Brian Goldman joins me now to talk about it. Hi Brian.

BRIAN GOLDMAN: Hi, Bob.

BM: Now, you spoke with someone who works in an extreme heat environment. Tell me about her.

BG: Her name is Britnee Miazek. She's an iron worker apprentice based out of Sault Ste. Marie, Ontario. And she works on top of a coke oven, which is used in steel production. So picture a giant open metal box that's outside. There's fire, there's smoke. It's giving off really high heat and it's all seasons, including summertime. She's got a blow torch. She's welding on top of that in a full jumpsuit, helmet and respirator. That's a description of hell. I would say the oven is outside so when it's 40 degrees Celsius it's even hotter.

BM: Wow. Boy, so how has Britnee's health been affected by all of that heat?

BG: While she's working, she gets symptoms of heat exhaustion, something I see in the emergency department all the time. Things like fatigue and dizziness. After three months or more of day -to -day exposure to those conditions, Britnee stops getting her periods. And the US Centers for Disease Control says that excess heat might affect both men's and women's fertility and overall reproductive health. That's according to studies from decades ago, which also showed a link to birth defects. Brittany didn't get answers from her doctor. So we brought her to a lab at Brock University in St. Catharines, Ontario where researchers are studying the immediate effects that heat has on workers.

BM: So what did you find out when you brought her into the lab?

BG: They placed Britnee in a room that was 40 degrees Celsius with 50% humidity for an hour in full gear, protective jumpsuit, respirator, the whole bit. She did four cycles each with five minutes of treadmill. And then she did weights where she was placing a weight, taking it from the floor, putting on a table. It's a standardized kind of measure. And then the third five minutes would be rest. And then she would do that all over again. So we watched her do all four of those by the fourth cycle, her face was beet red. She was sweating profusely. She looked exhausted. Sounds like torture. It was torture. And she kept, she's a gamer. She kept saying, I'm okay. I'm okay. And they measured her temperature, her core temperature went up because her body was unable to get rid of excess heat. Her heart rate was up 50 to 60 beats per minute, which meant it was working hard.

BM: Boy, so what does that mean for the rest of us?

BG: Britnee represents the sharp edge of the spear. She's young and she's in shape and she's working under extreme conditions, extreme heat. As temperatures rise, we're going to be exposing many more workers to extreme heat, including older workers, those with chronic ailments. It means we're going to see a lot more heat related illness. And my research colleagues tell me to look for a bump of people, Canadians, with excess kidney disease brought on by chronic exposure to heat.

BM: Wow. Thanks, Brian.

BG: You're welcome.

BM: That's Dr. Brian Goldman, host of CBC's White Coat Black Art. You can listen to Britney's story today on CBC Radio 1 at 1:30 pm or wherever you get your podcasts.

Studying the impacts of heat in the lab will tell you a lot about the adverse effects of heat. But we need to study it in the streets as well, to map the experiences we have of urban heat and how it affects our health on a much broader scale.

Which brings me back to Montreal, on a busy street corner.

There are cars and trucks whipping by… pedestrians walking up a big hill… some tree cover… it's a perfect spot for epidemiologist Scott Weichenthal and his PhD student Alessya Venuta to collect some data.

ALESSYA VENUTA: There we go! That's it. Goes up in a minute.

BM: And the sensor just clicks up under here?

SCOTT WEICHENTHAL: It's inside.

BM: So that's it? It just sits there?

SW: It does, but you have to do that 200 times. So we have to drive out to all the 200 locations, and pick them all back up, and then download the data, so it can be a lot of work.

BM: Dr. Weichenthal is installing sensors around Montreal to get similar fine level heat data as Dr. Ziter. But again, he's an epidemiologist – so he's interested in finding trends about how this heat affects people's health.

SW: Climate change, of course, is, we think, probably the greatest challenge of our time in terms of human health. And we really wanted to do an in-depth study looking at how heat varies across our cities because we know that there can be these localized regions of heat that could be important for health. And so what we're trying to do is really put out a very large number of monitors across large Canadian cities to really try and understand how populations are exposed to heat on a very fine scale.

BM: So can you show me one of your sensors? Do you have one?

SW: Yeah. So they're just a small little white box sensor. That's it? That's smaller than a cellphone. It's much smaller than a cell phone. It's like a cell phone in, you know, 2005 or something. Yeah. Yeah. A flip phone or something, Right. Yeah. Well, and so in here there is a temperature sensor and a sensor for relative humidity. So we have literally 400 of these. Wow. And, and we put 200 in Montreal and 200 in Toronto.

BM: Where do you put them?

SW: Everywhere. So we put them on street poles mostly. And so in collaboration with the cities, we basically, how we start as we sort of generate 200 random spots across the city and then we move those spots around to make sure we get pretty uniform coverage. Ok. And ultimately, we also build models using these data to predict temperature everywhere in places where we don't have measurements.

BM: So then how do you correlate that map that you get of the temperature differences across the city with the effects on human health?

SW: Yeah. So we have these models now that we can predict a daily spatial temporal variation in, in the temperature, and then we link that up with say hospital admission data. So we do studies where essentially we compare, you know, what was the temperature at your residence on the day you had a heart attack compared to days in that same month where you didn't have a heart attack. And we do these models to estimate sort of what's the short term impact of heat on, you know, cardiovascular mortality, respiratory mortality. Recently we've looked at mental health outcomes.

BM: So can I, can I see some of your results?

SW: Absolutely. Come look at some of our plots. So here's a plot that Alessya made, each one of the dots is one of our sensors. So this is a hot day in Toronto, and we see that the downtown area is, you know, around 40° on this very hot day because there's not a lot of green space around. And then there are areas that are sort of more green areas, more residential areas sort of north of the city around 32°. You can see that the sort of areas in the east of Toronto that are sort of bordering on the greenest areas are say 27° where the downtown is in, you know, the 40s. That's incredible, right? So there's this wide range of temperatures across the city, right.

BM: But this team is taking this research a step further, looking at how indoor temperatures factor into health risks.

SW: So we've also done some comparisons of indoor outdoor temperatures in homes with and without air conditioning. And so I'll show you the one with air conditioning first. And so the blue line here is the outdoor temperature. And the indoor temperature stays between 23 and 24° because it's an air conditioned home. So they have the thermostat set inside a very narrow range.

But when you look at a home that doesn't have air conditioning, this is for exactly the same period. So the outdoor temperature is exactly the same. But what you see is that in the home without air conditioning, the indoor temperature continues to rise, right? So at night time it goes down, but it doesn't go all the way down and then it's hot the next day, so it goes up a little higher. Right.

So every day it's getting a little warmer inside. And so it doesn't really cool off inside until the outdoor temperature goes down and stays down for a couple of days. So if you don't have air conditioning and you have a heat wave, it's just getting incrementally hotter and hotter and hotter inside your home. And, you know, that becomes dangerous for people who are at risk. So it's cumulative. I didn't realize. Yeah. And what's interesting to me is that just that, the degree to which the indoor temperature just doesn't decrease as much, right? So you can see even at night, the outdoor temperature is going down from say, 30 to 22, but the indoor temperature is only going from 29 to 28, right? So it's just not, because of the built environment and the impact of that on indoor temperature. It's just not having a chance to cool off.

BM: So then what does a lack of air conditioning do to a person's health?

SW: Yeah. So you can imagine that, you know, our bodies like to be at a certain temperature right around 37°. And, you know, we have a number of ways to, to counteract that through sweating and, and through changes on how our cardiovascular system works. But if you're someone who is sensitive to heat, right, who maybe your, your system is not in a state that's, you know, responding in the same way a healthy person would, this incremental increase in your indoor temperature is just putting more and more stress on your system. And if you're not capable to, to deal with it appropriately, that's when you know, the risk of these adverse events, I think is going to happen.

BM: So the heat builds and builds in homes without air conditioning during a heat wave, giving the residents inside no relief. This research is still in early phases, but Dr. Weichenthal believes that as this work continues, he'll see a strong tie between this buildup of heat and adverse health issues.

SW: Certainly we know that that heat is going to have an adverse impact on health. That's not surprising. What we don't really know is, what populations might be more exposed and more at risk than others. And then within those populations, you know, what's the prevalence of air conditioning use? So, and if you do have air conditioning, how much protection does that provide you?

BM: We're focusing on cities in today's program, but there's much to say about heat's impacts on the natural world.

Scientists are just starting to get a clearer picture of how heat is affecting the non-human animals on our planet as well. For example, a recent study out of Denmark showed that after just three hours in 40 degree temperatures, bumblebees virtually lose their sense of smell.

Another study out of University of California, Davis found that a springtime heatwave can leave baby birds struggling to survive, especially in agricultural areas.

Warming waterways are also a grave concern for all the life that can be found within. For their contribution to the Overheated series, CBC's climate solution show, What on Earth, looked at how heat affects one species in particular: the Chinook salmon in the Yukon River and the Bering Sea.

What on Earth host Laura Lynch is with me now. Hi, Laura.

LAURA LYNCH: Hi, Bob.

BM: Now you went to Whitehorse to find out about the Chinook salmon in the Yukon River. What's happening to that species?

LL: It's not good. I spoke to Elizabeth McDonald, she's a manager of fisheries for the Council of Yukon First Nations, and she's also a biologist. And she explained it to me this way. Warmer water is changing the food that is available to the Chinook. They're eating food that's less nutrient dense like jellyfish and at that same time the warmer water is increasing their metabolism so they're eating food with fewer nutrients when they actually need more energy in the warmer water. So the Chinook in the Yukon River, you may or may not know, they have the longest salmon migration in the world. Some of them travel around 3 000 kilometers over two months to reach their spawning grounds. Wow. Yeah, and Elizabeth described it as a marathon. It's longer than a marathon as far as I'm concerned, and they're doing it under ever more difficult conditions now. She described it as running a marathon, having a headwind when you're running up a hill.

BM: And not eating nutritious food. So how are these warmer waters affecting the health of the Chinook?

LL: Well, there's been an increase in a disease called, let me see if I can say this right, Bob, ichthyophonus. But they like the shorthand, they just call it ick, which seems rather appropriate. Elizabeth said the Chinook seem to get this disease more during warm ocean years when they're weaker and more vulnerable because of what we talked about before, the lack of nutrients. And she said ick really is icky. When you open up a fish that has been infected with ick, you see these, forgive me, little white pus pockets in their flesh and their hearts, their muscles and their flesh. It becomes kind of soft and mushy. So people don't want to eat the fish that's infected and it doesn't, doesn't smoke properly. It doesn't dry properly. And because the fish don't eat during that marathon migration up the Yukon and they're also fighting off this raging infection at the same time, it takes a toll and more of them die and they never reach their spawning grounds.

BM: Boy, well what effect is all of this having on the salmon migration numbers?

LL: Yeah, listen to this. They've been dropping for a long time, but the past few years have just crashed. 2022 and 2023 saw the worst numbers on record. The count was 12000 two years ago, 15000 last year, way down from the hundreds of thousands that happened back in the 80s. And all of this finally led the governments of Canada and Alaska to impose a seven-year fishing moratorium on the Chinook this past April to try to help the species recover. So that seven years, Bob, is one full life cycle for the Chinook salmon. And I was there during salmon migration season. It's looking as if this year's numbers might be a little bit better, but no one is really celebrating because they're still devastatingly low. And you should know that some Yukon First Nations people voluntarily stopped fishing for Chinook a long time ago. Because for them, the Chinook isn't only an important food source, it's also vitally important for their culture and their traditions. And those nations are pushing now for the government to take even more steps to protect and hopefully bring back the Chinook in greater numbers.

BM: Well, I look forward to hearing more. Thanks, Laura.

LL: You're welcome.

BM: Of course, this topic is a big one, and you can hear more about the effect of heat on the Chinook salmon and how First Nations are trying to help them on What on Earth? That's Sunday at 11.

BOB MCDONALD: In some ways, the fact that cities get hot, and need to be made cooler, is not new information. The knowledge that how we build our cities can increase temperatures has been around for a while.

Scientific studies into what was then called the 'city temperature effect' can be found dating back to the 17th century.

And while air conditioning these days is a key component of staying cool, it's not perfect. First of all, not everyone has access to it. But also while running air conditioning cools the indoors – that heat has to go somewhere. A recent study in London found that it can heat up the surrounding area by one degree.

But there are plenty of other ways to cool our cities. We can look at other parts of the world, and other moments in time, for inspiration.

Here's producer Amanda Buckiewicz with some "cool" ideas.

AMANDA BUCKIEWICZ: What many of us think of as unbearably hot temperatures are nothing new for lots of people around the planet. Long before we had electricity and air conditioning, our ancestors were coming up with some pretty interesting ways to beat the heat in the world's cities, and we are still learning from them today.

One great example comes from ancient Persia. Three thousand years ago, they developed a technology called "qanats." These are underground channels which use gravity to bring water from distant mountainous aquifers into cities to cool them down through evaporation. Thousands of these channels still operate across the Middle East today.

In ancient Greece, buildings were often white because of the availability of white marble and limestone, and their now-iconic whitewashed architecture was also practical, in that it reflected incoming sunlight. They also had plenty of fountains, which have been shown to cool the surrounding area by up to 3 degrees Celsius.

Nowadays, cities around the world are still using shade and water evaporation to bring temperatures down, but with some modern-day twists.

In downtown Singapore, a man-made forest made up of 18 artificial structures called "supertrees" stretch up to 50 metres into the air. These trees collect rainwater, act as vertical gardens, and generate solar power. They're a part of a 250-acre nature park called Gardens by the Bay.

Other projects are less high tech. A few years ago in the town of Alhaurín De la Torre in Southern Spain, the city council asked a local crochet teacher and her students to knit together some sunshades. And boy, did they deliver. Now, this patchwork of colourful crochet creations brings shade to over 500 meters of pedestrian walkways.

So what might we be using in the future to keep our cities cool? There are a number of new technologies in the works.

Several teams in Canada in places like Winnipeg, Vancouver and Toronto — and around the world — are developing living building materials with fungi. The goal there is to construct buildings that breathe to better regulate indoor temperatures without the need for air conditioning.

Researchers from the Spanish National Research Council are investigating the best reflective materials to beam the sun's radiation back to space. One idea is to mix sea snail shells into concrete to maximize its reflectivity.

And in Montreal, researchers at Quebec's École de Technologie Supérieure are working on ways to make asphalt less likely to trap heat by combining different recycled materials in its construction. They found that using yellow clay brick can increase reflectivity by 250% and drop surface temperature by 23%.

So there is no shortage of ways to keep our cities cool - it's just a matter of putting the right ones into action at a big enough scale to make a difference.

For Quirks & Quarks, I'm Amanda Buckiewicz.

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BM: Thanks Amanda.

Change is happening - slowly, but it's there. All of the research is now culminating in municipalities, developers, landscapers, and even homeowners thinking about their role in mitigating heat.

But to start with, we can look to nature for a little help with our overheating issues. Urban Ecologist Dr. Carly Ziter thinks there are many possible solutions, but an essential one is to build up the urban forest.

So Dr. Ziter, is the solution just to plant more trees? I mean that seems a little too simple…

CARLY ZITER: So that's certainly part of the solution, but unfortunately, no, it's not quite that simple.So really when we're dealing with extreme heat, we need a portfolio of solutions that includes multiple approaches. So that includes changes to the kinds of building materials we use, for example, using lighter coloured or cool pavement or built shade structures. It means planting more trees and vegetation. It also means social solutions, ensuring that everybody is aware of extreme heat events. And has access to a cooling centre. Ensuring that we check in on our more vulnerable friends and neighbors during the heat, and so, planting more trees is one part of a much more complex solution to adapting to climate change.

BM: Now, does it matter what kind of tree that you plant and is there a sort of a maximum or minimum tree cover that you need to be effective?

CZ: A larger tree that casts more shade is generally going to reduce the temperature further. And at the scale of a neighborhood, levels of canopy up around 30 or 40% tend to have the strongest effect. But something we also want to consider is the diversity of trees. I'm often asked what the best tree is. And I tend to say the best tree is a tree that's different from the one next to it. Because what we really want is, you know, different species, different sizes, different shapes, different ages. And the reason for that is we want our urban forest to be resilient. We don't want to lose too much of our canopy to any one shock.

BM: So our urban forests need biodiversity just like the natural forests do.

CZ: Absolutely. You know, we, we think of cities as this thing that's separate from nature or separate from you know the outside world, but we have, you know, thriving ecosystems right here in our cities and just like broader, bigger ecosystems, they need to be biodiverse in order to withstand what the world throws at them.

BM: Of course many municipalities across Canada have tree programs in place to protect the trees that already exist and plant more trees wherever possible.

But nature can't do the job alone. We also need to think seriously about changing the way we build our cities, and our roles as residents of those cities. Here's urban Ecologist Melissa McHale:

MELISSA MCHALE: I think cities are the answer. You know, we talk a lot about how many problems cities cause, but they house most of the people. They can be really efficient. People are so creative and can create ecosystems from scratch that provide lots of benefits. I think all of the answers exist right on our doorsteps and we just have to work together to make it happen.

BM: And it is possible to future-proof our infrastructure.

ROBIN HAWKER: Building design and redesign is such a critical opportunity for actually seeing climate adaptation and action in play. And so it's really exciting to see those climate resilient strategies being put in place and actually constructed.

BM: This is Robin Hawker. She works for an environmental engineering consultancy called Introba, where she leads their climate risk and resilience practice for building systems.

That means firstly she helps developers construct buildings that can withstand the worst that climate change can throw our way. But they also incorporate the latest technologies to keep from contributing to climate change as much as possible.

The company is [working with] the new St Paul's Hospital in Vancouver, which is the first health facility in BC that's being built and designed with climate change in mind.

From the beginning of the design process, the team incorporated the most drastic climate change projections to the year 2080 for both extreme heat events and flooding.

RH: Very early on in the building design, the building was designed to actually reduce the amount of heat it absorbs. So installing thicker insulation, higher performance windows to keep solar energy out, and ensuring that it has a really tight envelope so that air doesn't infiltrate in or escape out as easily. They thought about how they wanted to orient the building so that the amount of sunlight hitting the windows could be minimized.

And something that's really cool about the mechanical cooling system is that they've implemented a grey water reuse system for the water used in the cooling system. So what that means is the hospital captures rainwater, stores it on site, and then uses it to pass through its chillers to cool the hospital.

BM: When it opens in 2027, the hospital will feature not only a green roof, but a reflective cool roof as well.

RH: The new St. Paul's Hospital has 17 green roof spaces with a total area of approximately 2000 square meters, which is a huge amount of green roof area. And then in addition to that, they prioritized using lighter coloured roof pavers and pavements to help reflect solar energy to prevent that absorption and heating in building and site materials.

BM: Some researchers believe that cities themselves have to be part of the solution to our hotter future. We just have to empower people to think of our roles in an urban ecosystem in a different way.

Dr. Melissa McHale is an Associate Professor of Urban Ecology and Sustainability at the University of British Columbia.

BM: So why did you bring me here to Tatlow Park in downtown Vancouver?

MM: Well, because we were talking about heating. And what I noticed on the hot days this year, since I live in this neighborhood, is that people were coming to this location to feel cooler.

BM: Well, it's definitely that. I mean, it's got tall trees, got a lot of grass. And there's also a creek over here. Tell me about this.

MM: Yeah. So this is a stream that's been daylighted by the city of Vancouver just recently. It's just opened up this summer.

BM: When you say daylighted, what do you mean?

MM: Well, all that water used to travel to the ocean over here, in a pipe and now they have actually opened up the pipe and created a riparian area and a way for water to flow more naturally.

BM: Oh I see, so the this creek was totally covered over before you couldn't see it at all.

MM: So not only did they open up the stream, but they've built these little meadows and wetlands, which can actually have a significant contribution to cooling.

BM: I understand that Phoenix, Arizona, which is built on a desert, is doing some innovative things. Tell me about that.

MM: Yeah. So my colleagues in Phoenix have been studying heat for a while, of course, because it's one of the hottest cities in the world. And it's interesting there when the the city was trying to figure out the best way to treat wastewater. They decided that they're going to try to also build a wetland. So the Tres Rios wetlands are an area right next to the Salt River, and this wetland in a desert has been created entirely by humans and has all kinds of positive effects. People are using it a lot, just like they're using these walkways along the water. People tend to like to be near water. But also it's impacting biodiversity in a positive way and even migrating birds are stopping over to the wetland that's been created by people.

BM: Wow. So how important are the people in the process here?

MM: It's all about people. You know, when we're thinking about building climate resilient communities, a lot of times we're focusing on trees or infrastructure or green infrastructure. But the conversation really has to start with people. I think solutions should really be created on a neighborhood level. And every neighborhood has a different context, has a different set of challenges that they're facing.

BM: OK, so we're coming out of the park onto the street now. What did you want to show me here?

MM: Can I walk you down to this bus stop over here? Let's take a look. Because one of the things we're studying is bus stops. People can get really hot and uncomfortable while they're waiting for the bus. And also if you're looking for places to mitigate heat, why not choose places that can impact a lot of people at once.

BM: I've been to Phoenix in the summer time and when you're waiting to cross the street, you'll even stand in the shade of a pole just to get out of this sun, anything works.

MM: That was my experience! Holy cow, my first time in Phoenix there was people standing in a diagonal and I just couldn't understand why until I got up there and I realized that they were all just standing in the shadow of this pole just like that, across the landscape, it was brilliant. So now, OK, across the street is a bus stop, right? You can see that there, and there's no shelter there. There's no places for trees along the street, right? Because you have this walkway and so really the only tree that provides shade to this bus stop at a certain time of day is this one on a private residence. Right.

So is this another place that I wanted to bring you, this little corner. So did you notice what happened as we were walking down the street, there was a lot of spaces where there was a lot of sun. But now we're in a place that has a lot of shade

BM: The temperature is amazing, the difference.

MM: It's really, right. So highly variable. But the reason we're in shade here is, again, because of what this residence has done in terms of planting vegetation.

BM: They've completely covered their front yard. You can't even see the house. There's so much stuff here. There's a hedge, there's brushes and then there are tall trees over top.

MM: Yeah. So this place has a lot of vertical structural complexity and which we think is also important for cooling. So you have lots of different vegetation playing a role, not just trees alone. And also this landscape is beautiful. A lot of people walk by it and find their walk more aesthetically pleasing because the different flowers that bloom at different times of year. You know, we found in Denver that when people found an environment more aesthetically pleasing, they were likely to feel cooler.

BM: But you're also bringing up another topic, which is decisions people have to make if they own property on how they're going to use that property. How does that factor into it?

MM: It's so important, that's why I study residential landscapes a lot because 80% of cities is owned by private residences, right? So we can't actually come up with climate solutions. Cities only have a certain amount, the municipality itself only has a certain amount of space to actually implement solutions. We need all of our residents playing a role in this.

BM: It seems like a lot of the solutions are there, but we're not doing it. Why do you think that is?

MM: This is the conundrum. The world is heating up. Our cities are heating up. But the solutions for that take time. A tree doesn't grow in a day. If we can invest in these kinds of local solutions and helping people make the most out of the spaces around them, then our cities are going to be climate resilient in the future.

BM: Dr. Melissa McHale is an Associate Professor of Urban Ecology and Sustainability at the University of British Columbia.

We've been watching climate change as an oncoming freight train for 40 years. And now it's here. And it's here where we live, in our cities, which will, in the future, experience extreme heat like never before.

And the thing that I've learned from making this program is that we can do something about this. It's a matter of our sidewalks, our streets, our lawns and gardens, our parks, and our buildings. On a bicycle, or even while walking, you can see that the design of every space makes a difference. And that's why we should be thoughtful about it.

So we'll give the last word to Melissa McHale:

MM: Once you start thinking about microclimates and heat, you just can't stop. You pay attention to everything. Every bit of shade, every child on a playground, schoolyards. You just start thinking about place in a different way.

BM: This has been Overheated, a collaboration looking at different aspects of our warming world, between Quirks & Quarks, What on Earth and White Coat Black Art. Make sure to check out our sister programs on radio, on demand, or through their podcasts.

This program was produced by Amanda Buckiewicz with additional field production by Jennifer Wilson and help from Sonya Buyting. Jim Lebans is our Senior Producer. I'm Bob McDonald, thank you so much for listening.