An analysis of sediment cores from the burned area at the Anaktuvuk River in Alaska revealed that the fire there in September 2007 was the most destructive tundra fire at that site for at least 5,000 years - with more than 1,000 km2 burned. For the past 60 years, annual mean temperatures during the June-through-September time period in the Alaskan tundra have fluctuated between about 6 and 9 °C, with temperatures trending upward since 1995. In 2007, the year of the historic fire, the mean temperature was a record 11.1 °C, while precipitation and soil moisture dipped to an all-time low. Due to climate change the tundra will burn more frequently.
The Anaktuvuk River Fire coincides with extreme sea ice retreat, and tundra area burned in Alaska is moderately correlated with sea ice extent from 1979 to 2009. Recurrences of large tundra fires as a result of sea ice disappearance may represent a novel manifestation of coupled marine-terrestrial responses to climatic warming.
Gas locked inside Siberia's frozen soil and under its lakes has been seeping out since the end of the last ice age 10,000 years ago. But in the past few decades, as the Earth has warmed, the permafrost has begun thawing more rapidly, accelerating the release of methane - a greenhouse gas 23 times more powerful than carbon dioxide - at a perilous rate.
Global warming is amplified in the polar regions. What feels like a modest temperature rise is enough to induce Greenland glaciers to retreat, Arctic sea ice to thin and contract in summer, and permafrost to thaw faster, both on land and under the seabed. The Arctic is responsible for up to 9% of global methane emissions. Other methane sources include landfills, livestock and fossil fuel production.
Permafrost is defined as ground that has stayed below freezing for more than two consecutive summers. Most of Siberia and the rest of the Arctic, covering one-fifth of the Earth's land surface, have been frozen for millennia.
Capture: This figure shows the mean extent of permafrost in the Arctic, estimated for (a) the years 1990-2000 and (b) the years 2090-2100. In (c), the estimation of loss of permafrost by 2100 is overlaid on estimations for the year 2000.
Credit: A. David McGuire