SEATTLE -- Each fire season is a roll of the dice.
Some years lightning strikes more often. Other years soggy summers keep big burns at bay.
This year more than 4,000 wildfires burned almost a million acres across the Northwest. That might sound like a lot, but it falls below the 10-year average. In the last decade, only one year has had fewer fires than this year.
Scientists are quick to point out that no single fire season can be attributed to changes in the global climate, but as summers in the western half of the United States become drier and warmer, the chances of bigger, longer smokier fire seasons is expected to increase.
has found that by 2050 the wildfire season for the western United States will be about three weeks longer and be up to twice as smoky because of changes connected to global warming. And specifically in the Pacific Northwest, the area burned during the month of August could increase by 65 percent.
鈥淲armer and drier summers -- that鈥檚 the right climate recipe for large regional fire years,鈥� says University of Idaho climatologist John Abatzoglou, who studies regional impacts of climate change and how humans will be affected. 鈥淯nder a changing climate, the likelihood of seeing conditions conducive to these large regional fire years are going to increase dramatically.鈥�
With larger, longer-lasting wildfires, air quality is projected to suffer. Based on the amount of on-the-ground biomass available to be burned, .
Wildfire smoke is made up of tiny organic and black carbon particles that are a fraction of the diameter of a human hair. These microscopic particles can travel deep into the lungs and even cross over into the bloodstream. Inhaling those fine particles isn鈥檛 good for anyone, not even healthy people. Smoke can irritate the eyes and airways, leading to coughing, headaches, scratchy throats and runny noses. And for some people, wildfire smoke can be life threatening. It can trigger asthma attacks, heart attacks and even strokes.
Wildfire smoke is already one of the biggest drivers of degrading air quality throughout the Northwest. Over the past few months, wildfires have created hazardous and smoky conditions, and clouds of smoke as big as thunderheads billowed over communities in Southern Oregon and Central Idaho.
More than 50,000 acres of forest burned in August in Southern Oregon. Dense wildfire smoke caused particle pollution to reach unhealthy levels for more than a week straight in communities like Merlin and Grants Pass. The Red Cross handed out more than 20,000 respirator masks there to help people avoid breathing smoke from wildfires that burned near the Rogue River. .
Similar conditions plagued Eastern Washington in the fall of 2012. Lightning strikes started 100 fires that burned more than 200,000 acres, causing the highest smoke concentrations ever recorded in several Washington communities, according to the Washington Department of Ecology.
In Wentachee, Wash. last year air pollution was monitored at levels considered hazardous by the EPA for 14 days. More than 50,000 masks were distributed to help prevent smoke inhalation. And during that time, .
Since the 1980s, the overall number of wildfires and the amount of acres burned in the United States has increased steadily. As the climate has warmed, snow melts earlier and dry periods have lengthened both of which favor fire conditions, says Jennifer Pierce, a professor in the Geosciences Department at Boise State University, studies the history of fire going back hundreds and thousands of years.
But Pierce points out that even after you account for fire suppression, climate change is still a factor. Places like Yellowstone National Park, which have experienced larger wildfires in recent decades, never had active fire suppression.
鈥淚t鈥檚 pretty remarkable when you put all the data together and the cause of those large fires is overwhelmingly climate,鈥� Pierce says.
When Idaho journalist Rocky Barker reported on large wildfires in the 1980s, he had no way of knowing that he was at the beginning of what he would later recognize as a generation of large fires and longer fire seasons. To Barker, the fire that kicked it all off was 1988 fire in Yellowstone National Park, which burned more than 150,000 acres a day in late August and early September.
Back then that kind of extreme fire behavior was unusual, Barker says. Now it鈥檚 become much more common.
In the decades since, Barker has seen communities hit repeatedly with fires that were so big that residents have been required to evacuate. And the impact of smoke from wildfires also drives people away.
鈥淟iving in a season of smoke is really hard. Last summer and this summer I鈥檝e been in communities where people just didn鈥檛 go to work because it was just too smoky,鈥� says Barker, author of the book, . 鈥淚 don鈥檛 think people can even fathom yet how much change fire is going to continue to bring on us.鈥�
Story by Katie Campbell with additional reporting by Amelia Templeton and Aaron Kunz. Video by Aaron Kunz and Katie Campbell. Wildfire acres burned chart built by Sarah Strunin.
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Wednesday: Scientists say hotter temperatures will bring about more fire seasons that are longer, drier, and likelier to fill the air with smoke that can make breathing more difficult.
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