In the damp and dreary Pacific Northwest, where moss climbs the trees and moisture dribbles down lamp posts and seems to seep through almost everything, the reward for surviving another year wrapped in oppressive mist and grey clouds used to be a lush, bright, sky-blue late summer.

"Most folks I know tend to try not to leave Seattle in August," says Karin Bumbaco, Washington State's assistant state climatologist.

But for much of the last two weeks, air over three of North America's dampest, cleanest cities was dingier than the skies over Mumbai, Jakarta, and every major industrial city in China. For a brief period Wednesday evening, when it comes to the fine particles of pollution that can lodge in your lungs and make breathing difficult—even if you're a healthy adult— the dirtiest major city on earth was Vancouver, British Columbia. Seattle and Portland rounded out the top three.

View Images A bicyclist in Seattle wears a mask. Photograph by Jovelle Tamayo

The hundreds of wildfires burning in almost every direction for weeks has transformed the Northwest into a gauzy orange blanket of haze, trapping entire cities in their homes, putting agriculture workers at risk, and even straining life for some animals. In a region known for its clean air, dangerous skies in August have become the norm in three of the last four years.

As climate change warms the West's forests, setting the stage for ever-bigger and longer-lasting fires, a growing, overlooked threat is the risk from smoke. Earlier this year, the Environmental Protection Agency reported that wildfire smoke now accounts for 40 percent of the country's particulate matter pollution.

"In the coming decades, we think wildfires could as much as double across the West," says Andrew Wineke, a spokesman for the Washington State Department of Ecology. "What's going to happen to all that smoke?"

Nowhere has that smoke been more visible this year than in the Pacific Northwest.

Wildfires 101

Calls To Stay Inside

For days on end this month, Seattle and Portland have faced warnings from state and local officials that the thick gauzy skies are actually unhealthy for adults and children alike. The air quality index for levels of PM 2.5, the small particles of pollution that can enter the bloodstream, frequently topped 150, which can irritate the eyes and spark coughing fits just spending time outdoors. In rural parts of the states, those numbers often topped 400.

NASA reported that smoke was so thick it could be seen on images from space. Hospitals have seen an uptick in respiratory complaints. Pools closed. Soccer practices were canceled, and apple pickers on the eastern slopes of the Cascade Mountains were encouraged to wear masks—when they were able to work at all. Seattle-Tacoma International Airport rerouted planes because visibility was so poor.

At the Seattle Aquarium, a sea otter with asthma was even treated with an inhaler, according to a report in The Seattle Times.

"It's pretty bad out there—it's just gross," says Kathie Dello, deputy director of Oregon's Climate Service at Oregon State University. "You wake up in the morning and the sky is brown and the sun is red and it's like that day after day."

Officials have encouraged people to stay inside with windows closed, but this is a region where few have air conditioning because temperatures, historically, rarely topped 80 degrees Fahrenheit. Portland this week broke a record for the most days over 90 degrees Fahrenheit, with 30. Seattle broke its record temperature by two degrees on Wednesday, hitting 89 degrees.

"There's this almost oppressive heaviness in air," Bumbaco says.

View Images The smoke from wildfires near Portland has obscured the usually visible Mount Hood. Photograph by Will Matsuda

Surrounded by Fire

In one sense, this particular summer is unusual. There are so many fires in so many places, Portland and Seattle are surrounded on three sides by enormous plumes of smoke—moving south from British Columbia, east from the far side of the Cascades and north from California and Southern Oregon. A fire is also burning in the typically rainy Olympic National Forest, between Seattle and the Pacific Ocean. So even when the winds shift, smoke has found its way in.

But 2017 saw 11 straight days of thick smoke in Seattle, Bumbaco says. Smoke also rolled through in 2015, and experts have been warning for years that the source—wildfires—will almost certainly get worse.