Retreat of sea ice feeds largest tundra fire in 5,000 years.
It started with a bolt of lightning.
A lightning strike on July 16, 2007, triggered a fire that swept across an area of Alaska’s vast, treeless tundra on the North Slope. The Anaktuvuk River fire was larger and hotter than the tundra fires that typically creep across the plain of northern Alaska. In fact, LAS plant biologist Feng Sheng Hu has now discovered it was the only large tundra fire in that area of Alaska in 5,000 years.
Fed by unusually warm and dry conditions in arctic Alaska, this tundra fire did not burn out until the beginning of October 2007, and by that time it had consumed over 600 square miles. But although lightning might have been the trigger, Hu says the real culprit is probably climate warming and the retreat of sea ice.
Sea ice reflects the sun’s rays, helping to keep temperatures cooler, he explains. But when sea ice retreats—as it has in the Arctic—that leaves open water, which is darker and absorbs the sun’s heat. This heat is then released back into the atmosphere during late summer and early fall, further boosting temperatures and setting the stage for tundra fires.
“The tundra has always had small fires, but big ones have been very rare,” Hu says.
In their research, Hu and his University of Illinois team often look far back in time, trying to determine what the climate was like thousands of years ago and how it affected plants and other life. This helps them to understand just how unique today’s warming is, and whether it fits into a natural cycle or is human-induced.
In addition to Alaska, Hu and his students have conducted research in other places, including Siberia, Africa, and Australia. They use a wide array of tools such as pollen identification, DNA sequencing, computer modeling, and isotope geochemistry.
In the case of the Alaskan tundra fire, Hu’s team set up floating platforms on two lakes within the region burned by the Anaktuvuk River fire. From these research rafts, they drove steel poles into the bottom of the lakes, pulling up sediment samples. Then they analyzed the sediment for charcoal particles, which would be present at different layers if tundra fires had occurred there in the past.
Hu looked back 5,000 years and found no trace of charcoal, showing that there hadn’t been a tundra fire in that region during the entire five-millennia span until the Anaktuvuk River fire in 2007. He also says that if you look at records over the past 30 years, you see a steady decline in sea ice, while tundra fires appear to have increased correspondingly.
“We’re probably looking at a prototype of future changes,” he adds. “If our hypothesis is right, we’ll see more tundra fires.” This in turn might increase soil greenhouse emissions, change the types of plants in the tundra, and negatively impact the livelihood of indigenous peoples.