ARI SHAPIRO, HOST:
At some points this summer, the big city with the worst air quality anywhere in the world was not Beijing or New Delhi. It was Seattle, Wash. To talk about why and what this means for the future, professor Cliff Mass joins us now. He's a professor of atmospheric sciences at the University of Washington in Seattle. Welcome.
CLIFF MASS: Thank you.
SHAPIRO: Just describe how it felt when the air was at its worst this summer.
MASS: Well, it was the worst air that we've had in 20 years. And so the visibility decreased to, you know, maybe a half a mile at some points. And a number of people were wearing face masks and filters. And cold symptoms, things like that were really prevalent around the city.
SHAPIRO: This is a city where people take pride in their view of the mountains - no mountains visible.
MASS: That's right. I mean, we not only lost the mountains. We couldn't even see the water around us.
SHAPIRO: Wow.
MASS: I mean, the visibility really decreased to almost nothing at one point.
SHAPIRO: What made it so bad?
MASS: Well, the key thing was that we had wildfires that were fairly close in the North Cascades, and we had an atmospheric circulation that took the smoke directly from these nearby fires right over Seattle. That was enough to really give us the worst air quality in two decades.
SHAPIRO: Is this just a strange anomaly, or is this something that's going to become more common?
MASS: Well, this is the second year we've had this poor air quality. Last year, we had two incidents. This year, we had one. We've had some minor ones before, but people are really unnerved by the fact that it's happened two years in a row. Now, the question about whether it's going to happen in the future, I suspect the answer's yes.
SHAPIRO: Why is that?
MASS: Well, the big problem is our forests. We've suppressed fire now for almost a century. A lot of the forests surrounding Seattle are in very bad condition. They're overgrown. They have a lot of slash, a lot of low bushes and trees. And they're completely unlike the forests that were here 150 years ago. And the problem is when they burn, they burn catastrophically.
SHAPIRO: And I'm sure climate change doesn't help.
MASS: That's right. The question is how much of this is climate change. I suspect that only a small proportion of this is climate change. I think that the main problem is the forests, which are ready to burn. We have invasive grasses that have moved in that burn very easily. And human beings are increasingly starting fires with this huge number of people going in for recreation, other uses of the forested areas.
Now, on the long term, as the planet warms up, we certainly would expect more fires. So climate change, global warming probably contributed a small amount to it, but probably the key thing is what we've done to the surface of the planet.
SHAPIRO: Are there things that the government or citizens could do to try to prevent this from happening more?
MASS: Well, the key thing is to fix our forests. People know what to do. I mean, if you talk to the people in the Forest Service, it's clear. We have to thin the forests and then let fire come back regularly but at a much lower intensity.
SHAPIRO: This would be bad for any city, but Seattle is a city that takes such pride in outdoor activities - fishing, hiking, camping. Is this putting a damper on all of that?
MASS: Well, it not only put a damper on outdoor activities, even relatively indoor activities. Like, outdoor restaurants, ones that would normally be crowded, were vacant during the heavy, heavy smoke. People would - wouldn't go on the ball field or the playfields around here, so the tennis courts just were emptied out. So it changed everything in terms of what kind of recreation people were doing for that two-week period.
SHAPIRO: You're describing these problems in Seattle, but I imagine this could be the case with other cities that are surrounded by forest in the United States too.
MASS: Well, this is true of the entire western United States. The forests have been degraded everywhere from California to Montana. And it's also true of British Columbia. Quite a bit of the smoke that we had here this summer and last summer were from fires north of us, you know, hundreds of fires in British Columbia.
SHAPIRO: That's Cliff Mass, professor of atmospheric sciences at the University of Washington, speaking with us from Seattle. Thanks, and hope you breathe easy out there.
MASS: Thank you very much.
(SOUNDBITE OF UKIYO FEAT. JCAL'S "COLD FEET") Transcript provided by NPR, Copyright NPR.