Alaska On Pace for Worst Fire Season Ever

The Aggie Creek wildfire in Alaska. Fires here often burn below the surface of the ground. Alan Vandiver

It's not unusual for fires to break out in Alaska in the summer. But the number and extent of fires in the state has been increasing in the last two decades. This year is the worst yet. So far in 2015, fires have burned nearly 5 million acres, an area the size of Connecticut, which is the largest acreage burned year-to-date on record.

Many of the 300-some wildfires still burning in Alaska were set by lightning late last month. Seven of those are classified as large wildfires; The National Interagency Fire Center, which is tracking the fires, reports that four of these are completely uncontained. One cluster of blazes known as the Tanana area fires have charred nearly 500,000 acres, half the size of Rhode Island.

Fires in Alaska are unique in that they often burn below the surface, up to 10 feet or more below ground. Here lie thick piles of duff—dead leaves and trees and other organic material that cannot decay due to the cold temperatures. Just below this duff is a layer of frozen ground called the permafrost. These underground fires burn the duff and can melt the permafrost, wherein vast quantities of carbon are locked up.

The increase of fires in Alaska concerns researchers like Ted Schurr, who studies permafrost in Alaska during the summers. "It's understood that there's about twice as much frozen carbon [in permafrost] as there is in the atmosphere, to the tune of about 1,700 billion tons of carbon stored frozen," Schurr tells NPR. "The Arctic and the boreal regions are a hot spot of carbon that's stored in the biosphere that has some vulnerability of ending up in the atmosphere as the climate changes," Schurr says.

Wildfires here, then, threaten to disproportionately add carbon to the atmosphere, where the chemical element traps heat and further exacerbates global warming.

Wildfires tend to become more frequent as temperatures rise. And they certainly have in Alaska, by 3.4 degrees Fahrenheit over the past 50 years, according to the Environmental Protection Agency. That's twice the national average over the same time period.