MICHEL MARTIN, HOST:

If you live there, you already know - another punishing heat wave has begun in the northern Rockies in western Canada. This comes just weeks after a heat wave worked its way across the Pacific Northwest, bringing temperatures well above 100 degrees in places that rarely see anything close to that. And it's only now that we're beginning to get a clear picture of the death toll from that heat wave - nearly 800 deaths, according to officials across the U.S. and Canada, a number that is likely to grow as they take a closer look at the total excess deaths in the region. It's a dire warning sign for what could come with a changing climate.

So we wanted to find out more about this relationship between heat and public health. For that, we've called professor Kristie Ebi. She is a professor of global health at the University of Washington and has been studying the health risks of climate change for more than two decades. Professor Ebi, thanks so much for joining us.

KRISTIE EBI: And thank you so much for covering this story.

MARTIN: I just want to start with this relationship between climate change and public health as it relates to heat. And I have to confess my ignorance, but I think a lot of Americans are like me, and they think of heat as something that might make you uncomfortable but probably won't kill you like extreme cold. But I understand from you that that's wrong. So what does the research say about the threat to public health from extreme heat?

EBI: Heat is the No. 1 weather-related killer of Americans. And the estimates for how many Americans die every year in the heat vary from around 700 or so to a recent modeling study that says it's more than 12,000.

MARTIN: What is it that makes these heatwaves so deadly? Is it the fact that a lot of people don't see them as a threat?

EBI: There's very low awareness, as you mentioned, that heat is a threat and we need to take heat seriously, that people are not typically aware that our bodies function within a fairly narrow range. When we get too hot, there's a variety of mechanisms to bring our core body temperature down. Sweating is one that pretty much everybody's familiar with. And when that isn't sufficient, our cells or organs start heating up. If you've got underlying heart disease, respiratory disease, other kinds of problems, your organs come under a lot of strain and they can fail prematurely. So when we look after a heat wave, after we get all the death certificates in, you'll see that the excess deaths was much larger than the number that were originally recorded around the time of the heat wave.

MARTIN: But why do you think that more of us don't know this? Is it part because there are so many regional differences, like some parts of the country experience extreme heat, other parts don't, air conditioning is widely available in some places, other places not? I mean, I'm just - why do you think that is?

EBI: It's a really good question. We do know that our experience of heat very significantly for one place to another. You mentioned our temperatures in the Pacific Northwest, in Canada, very extreme for us, not that extreme for Phoenix. And where we live matters because our built infrastructure, the access to air conditioning, how we cool our buildings varies from location to location. But over and above that, people don't think of heat as something that they should be worried about. They think of something that's lovely. It's an 80-degree day outside. It's perfectly sunny in Seattle. We're all going to go outside. And we don't think about the risks that are associated with heat.

MARTIN: You know, the death toll was especially high in British Columbia, but there were also hundreds of deaths across Washington and Oregon. Why is that? And I ask for a couple of reasons. One, there's usually a bit of warning before you have an extreme heat event, right? So do you have a sense of, like, why were there so many deaths in those places?

EBI: This was just a textbook case of a heat wave where there is warning before the heat wave in a place that is not prepared for very extreme heat waves. The heat wave starts, there looks like there's just maybe a few deaths. It doesn't look like it's a really big problem. And then a couple of days later, you've got people in the emergency departments, you've got people in the morgue.

In Canada, there is much more rapid access to death certificates than there is in the United States. The numbers are still coming in in Canada, so it will be another month or so before all of the death certificates are in. The process in the United States is a little bit different. It'll take us months before we really can understand how many excess deaths occurred in Washington and in Oregon.

MARTIN: You know, the initial reporting says that there are experts who have been consulted about this, say that many of these deaths were largely preventable. What does that mean, and why is that?

EBI: I'm one of the people who keeps reminding everyone that almost all deaths in a heat wave are preventable. You think about the devastating floods this week in Germany, and you think about people who are washed away, people who are trapped in apartments, for example, during floodwaters or during a building collapse, there's things that are very difficult to prevent. But there's a century of understanding of keeping our core body temperature down, of making sure that people have access to a fan, that they can put water on themselves so that, as the water evaporates with the fan, they can cool themselves down. And they need to have access to city services in some cases to help them do so by going to a cooling center.

MARTIN: I think what I hear you saying is that the ignorance about the peril of extreme heat is widely shared, including among city leaders.

EBI: I will speak on behalf of the city leaders. I don't work for the city, but they did put up cooling centers. They did try to pull together services. And in their defense, putting these systems together requires more than a couple of days. The logistics involved are pretty significant. You think - you're going to open cooling centers, where are they going to be? How close are they to the most vulnerable? Do you know where the most vulnerable are located? How are you going to get to the cooling center? You're going to ask somebody who's particularly vulnerable to go walk to the bus stop and wait for a bus to take a bus there? There's lots of logistical questions. How do you interface with all the city services?

MARTIN: What I'm also hearing you saying is that people are going to have to think more about that. I mean, a study published this year in the journal Nature Climate Change found that more than a third of the total deaths due to heat waves can be attributed to climate change. What should we expect in the coming years? I mean, are these events likely to be more common?

EBI: We know from the climate science that climate change is increasing the frequency, the intensity and the duration of heat waves. We also have seen over the last few years very extreme heat waves in Siberia last year, where temperatures in the Arctic, I believe, were over 100 degrees. There was a heat wave in Japan that the Japanese meteorological authority said couldn't have happened without climate change. Northern Scandinavia, Sweden, a couple of years ago had a heat wave with 700 excess deaths. So we're seeing these around the world. And, yes, communities need to develop heat action plans to be prepared for a much hotter future.

MARTIN: That was Professor Kristie Ebi. She studies climate change and public health at the University of Washington. Professor Ebi, thanks so much for taking the time.

EBI: Thank you very much. Transcript provided by NPR, Copyright NPR.