Title Springtime warming and reduced snow cover from carbonaceous particles
Author Flanner, M.G.; Zender, C.S.; Hess, P.G.; Mahowald, N.M.; Painter, T.H.; Ramanathan, V.; Rasch, P.J.
Author Affil Flanner, M.G., National Center for Atmospheric Research, Boulder, CO. Other: University of California, Irvine; University of Utah; Scripps Institute of Oceanography
Source Atmospheric Chemistry and Physics, 9(7), p.2481-2497, . Publisher: Copernicus, Katlenburg-Lindau, International. ISSN: 1680- 7316
Publication Date 2009
Notes In English. Includes appendix; published in Atmospheric Chemistry and Physics Discussions: 26 November 2008, http://www.atmos-chem-phys- discuss.net/8/19819/2008/acpd-8-19819- 2008.html ; accessed in Apr., 2011. 77 refs. GeoRef Acc. No: 310586
Index Terms absorption; aerosols; albedo; climatic change; global change; global warming; human activity; ice; particles; reflectivity; snow cover; solar radiation; Eurasia; North America; atmospheric transport; black carbon; boreal environment; carbon dioxide; carbonaceous composition; climate change; climate forcing; global; greenhouse gases; organic compounds; reflectance; sea ice; seasonal variations; snowpack; solar forcing; terrestrial environment; transport
Abstract Boreal spring climate is uniquely susceptible to solar warming mechanisms because it has expansive snow cover and receives relatively strong insolation. Carbonaceous particles can influence snow coverage by warming the atmosphere, reducing surface-incident solar energy (dimming), and reducing snow reflectance after deposition (darkening). We apply a range of models and observations to explore impacts of these processes on springtime climate, drawing several conclusions: 1) Nearly all atmospheric particles (those with visible- band single-scatter albedo less than 0.999), including all mixtures of black carbon (BC) and organic matter (OM), increase net solar heating of the atmosphere-snow column. 2) Darkening caused by small concentrations of particles within snow exceeds the loss of absorbed energy from concurrent dimming, thus increasing solar heating of snowpack as well (positive net surface forcing). Over global snow, we estimate 6-fold greater surface forcing from darkening than dimming, caused by BC+OM. 3) Equilibrium climate experiments suggest that fossil fuel and biofuel emissions of BC+OM induce 95% as much springtime snow cover loss over Eurasia as anthropogenic carbon dioxide, a consequence of strong snow-albedo feedback and large BC+OM emissions from Asia. 4) Of 22 climate models contributing to the IPCC Fourth Assessment Report, 21 underpredict the rapid warming (0.64C decade-1) observed over springtime Eurasia since 1979. Darkening from natural and anthropogenic sources of BC and mineral dust exerts 3-fold greater forcing on springtime snow over Eurasia (3.9 W m-2) than North America (1.2 W m-2). Inclusion of this forcing significantly improves simulated continental warming trends, but does not reconcile the low bias in rate of Eurasian spring snow cover decline exhibited by all models, likely because BC deposition trends are negative or near-neutral over much of Eurasia. Improved Eurasian warming may therefore relate more to darkening-induced reduction in mean snow cover.
URL http://www.atmos-chem-phys.net/9/2481/2009/acp-9-2481-2009.pdf
Publication Type journal article
Record ID 65007015