In Alaska, where sea ice has shrunk to record lows in places and far-north temperatures have climbed to record highs, dozens of fires are burning the treeless tundra and releasing carbon into the atmosphere.
The latest flurry of Alaska tundra fires has been on the Seward Peninsula, which juts out to the Bering Strait.
On Wednesday, lightning strikes sparked 16 fires on the Seward Peninsula, 15 of them burning in tundra, Alaska fire managers reported. That added to several fires already burning there, and several more ignited the following day.
The northernmost Alaska fire, a 200-acre (80-hectare) blaze along northwestern Alaska's Noatak River and about 80 miles (130 km) north of the Arctic Circle, was sparked by lighting on Thursday, fire managers reported.
The large number of tundra fires is pumping smoke over the Bering Strait region and drawing scientists' attention.
At least some of the blame goes to "the very early ice loss and the extraordinarily warm sea surface temperatures," said climatologist Rick Thoman of the Alaska Center for Climate Assessment and Policy.
"That warm water is adding its heat to the atmosphere, allowing it to be warmer inland," he said.
More frequent fires
Although tundra fires have burned sporadically in Alaska in the past, their frequency is increasing as temperatures rise, near-surface permafrost thaws and other forces make the low-lying plants more flammable, scientists say.
A 2012 study led by University of Notre Dame wildfire expert Adrian Rocha found that Arctic Alaska tundra fires had increased in size over two decades. A 2015 study co-authored by Rocha predicted that Alaska tundra wildfire acreage will double by the end of the century.
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One of the most significant Alaska tundra fires was in 2007, when about 400 square miles (1,035 sq km) burned for months on the North Slope, the northernmost region of Alaska and a place where fires are rarer than in the Bering Strait region. That fire, named for the Anaktuvuk River, was linked to extraordinary Arctic heat and what was, at the time, record-low sea ice.
By thawing permafrost and releasing loads of sequestered carbon, tundra fires can have long-lasting effects. The 2007 Anaktuvuk River fire released more than 2.1 million metric tonnes of carbon into the atmosphere, University of Alaska Fairbanks scientists calculated, an amount they said was equal to the atmospheric carbon the entire Arctic used to absorb annually.
Eric Miller, an ecologist with the Alaska Fire Science Consortium, said northern tundra fires are known for triggering cascading effects.
"When you burn the tundra, you get that direct release of carbon into the atmosphere," he said. Permafrost thaw caused by fires primes the tundra for future burns by melting the ice that moistens soils, he said. "That stuff drains out, and you get future potential for fire after that," he said.