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Vegetation feedbacks to climate warming in Alaskan arctic and boreal ecosystems.
CHAPIN, STUART*,1, BERINGER, JASON2, EUGSTER, WERNER3, LLOYD, ANDREA4, LYNCH, AMANDA5, MCFADDEN, JOSEPH6, MCGUIRE, DAVID1, STURM, MATTHEW7, 1 University of Alaska, Fairbanks, AK2 Monash University, Clayton, Australia3 University of Bern, Bern, Switzerland4 Middlebury College, Middlebury, VT5 University of Colorado, Boulder, CO6 University of Minnesota, St. Paul, MN7 Cold Regions Research and Engineering Laboratory, Fairbanks, AK
ABSTRACT- Recent vegetation changes in northern Alaska include increased shrub density in moist tundra, increased tree density in forest tundra, and expansion of trees beyond the latitudinal treeline. Each of these changes increases the heat transport to the atmosphere by increasing radiation absorption (lower albedo) and the proportion of absorbed energy that is transferred to the atmosphere as sensible heat. The magnitude of these changes, on a unit-area basis, is similar to effects of a doubling of atmospheric carbon dioxide or a 2% change in solar constant, such as occurred at the last glacial-interglacial boundary. Climate simulations suggest that a change from shrubless tundra to shrub-dominated tundra on the North Slope of Alaska would increase July mean temperature by 1.5 to 3.5 degrees C, with the warming effects extending south into the boreal forest of interior Alaska. In contrast to these positive feedbacks to regional warming in tundra, an increase in fire frequency in the boreal zone would reduce sensible heat flux-- one of the few negative feedbacks to high-latitude warming that have been identified to date. If these vegetation feedbacks to regional warming are widespread, as suggested by indigenous knowledge, they may contribute to the summer warming that has recently been observed in northern Alaska.
KEY WORDS: arctic, energy exchange, vegetation change, climate change