covering central Alaska, July 2005
A new study published in Nature Geoscience suggests that huge forest fires in the Boreal Forests of Alaska, Canada and Siberia are causing global cooling. The basic idea is that after forest fires consume blocks of the Boreal Forest, they leave behind a land surface with a higher albedo, which cools the planet. In winter the burned over land is covered with snow (albedo = 0.9) and in summer the trees are replaced with bare ground, wildflowers, and shrubs (albedo = 0.6). In contrast, Boreal forest has an albedo of ca. 0.08-0.12, so that areas of burned over forests reflect 6 to 9 times more sunlight then a standing Boreal Forest. The smoke from forest fires also blocks some sunlight, and locally cools the ground.
The exact amount of global cooling caused by forest fires probably isn't very large, as even the largest forest fires in Alaska burn much less than 0.01% of the standing Boreal Forest, and forests become re-established in even the largest burned areas after a few decades.
These forest fires are an interesting example of the side effects of Global Warming. Temperatures in Alaska, Canada, Siberia and other high latitude areas are increasing much more rapidly then average global temperatures. Warmer air temperatures in Alaska are drying out the soil and making the forests more susceptible to forest fires.
The link between Global Warming and forest fires suggests that huge fires will become more common as global temperatures continue to rise. This is obviously bad news for the forests, but Alaskans don't like it either. Up until the late 1990s, it was rare for forest fires to cover the entire state with smoke. But since then, huge forest fires have become a regular and unwanted feature of summers in Alaska, and heavy smoke is often present for weeks over large parts of the state during June, July and August.
Large Forest Fires Have Become Common During the Summer in Alaska
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