Eugene S. Takle
© 2006
The Arctic is warming at an unprecedented rate. Sea-ice cover in the Arctic Ocean is at its minimum extent in more than a century. Recent reports suggest the Arctic Ocean is headed toward a seasonal ice free state - a condition that has not occurred for at least a million years. Part of the reason for this accelerated warming at high latitude is the positive feedback from reduced snow cover due to greenhouse-induced warming. The reduced snow and ice cover reduces reflection of solar radiation, which increases solar-induced warming, which further reduces snow cover. This positive feedback is included in global climate-model simulations of future climates. However, another feedback not accounted for in climate models may be leading to additional warming and positive feedback, according to research recently reported by Chapin et al. (2005) and overviewed by Foley (2005). Warmth in the tundra landscape is leading to northward expansion of the boreal forest and increased growth of shrubs. These larger plants on the former tundra landscape absorb additional solar radiation, which also contributes a positive feedback that is not accounted for in global climate models.
References
Chapin, F.S. , III, and Co-authors, 2005: Role of land-surface changes in Arctic summer warming. Science, 310, 657-660.
Foley, J.A., 2005: Tipping points in the tundra. Science, 310, 627-628.