Snow and Climate

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Changes in the duration of the snow season represent a strong positive feedback to climate warming due to the contrast in surface reflectivity between snow- covered and snow-free ground.
E. Euskirchen.

Modeling simulations over boreal Alaska have documented changes in albedo due to changes in the duration of the snow season and due to changes in the amount of young forest stands on a landscape due to changes in the fire regime. In addition, changes in the exchange of the greenhouse gases CO2 and methane have also been estimated due to changes in climate, atmospheric carbon dioxide concentrations, fire regimes, and methane emissions. The sum of these feedbacks indicates that changes in boreal Alaska acted to warm the atmosphere between 1970-2000 and between 2003-2100. The strongest feedback to climate warming was derived from a lengthening of the growing season (reducing the snow-albedo feedback) between 2003-2100, and this was only partially counterbalanced by the cooling effect of an increase in the amount of young stands in the landscape under more severe fire regimes, and increases in carbon uptake by terrestrial ecosystems between. Furthermore, under a warmer, wetter climate the amount of methane released from Alaska’s peatlands increased between 1970-2000 and between 2003-2100, acting as an additional positive feedback to climate warming.

Summary of changes in atmospheric heating due to changes in land surface albedo and carbon and methane uptake/emissions in boreal Alaska, from available estimates. A negative sign represents a negative feedback for a sink term and a positive sign represents a positive feedback for a source term.
Euskirchen et al., 2010.
For further reading: 
Euskirchen, E.S., A.D. McGuire, T.S. Rupp, F.S. Chapin III, and J.E. Walsh. 2009. Projected changes in atmospheric heating due to changes in fire disturbance and the snow season in the western Arctic, 2003 - 2100. Journal of Geophysical Research - Biogeosciences 114, G04022, 15 pages, doi:10.1029/2009JG001095.
Euskirchen, E.S., A.D. McGuire, F.S. Chapin, and T.S. Rupp. 2010. The changing effects of Alaska boreal forests on the climate system. Canadian Journal of Forest Research 40:1336-1346. doi:10.1139/X09-209.
Zhuang, Q., Melillo, J.M., McGuire, A.D., Kicklighter, D.W., Prinn, R.G., Steudler, P.A., Felzer, B.S., and Hu, S. 2007. Net emissions of CH4 and CO2 in Alaska: implications for the region's greenhouse gas budget. Ecol. App. 17:203 - 212.
For further information: 
Dr. A. David McGuire
Dr. Eugenie Euskirchen
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