RESEAU SOL(ID)AIRE DES ENERGIES !
Débat problématique énergétique / effet de serre / climat, etc.
EFFET DE SERRE
1) La neige sale est un contributeur important au réchauffement de l'Arctique
2) Dirty snow may warm Arctic as much as greenhouse gases
http://today.uci.edu/news/release_detail.asp?key=1621
Burning cleaner fuel would brighten snow and lower temperatures


1) La neige sale est un contributeur important
au réchauffement de l'Arctique
ADIT: http://www.bulletins-electroniques.com/actualites/43323.htm

     Une équipe de chercheurs de l'université de Californie à Irvine, menée par Charles Zender, s'est intéressée à la part que prenait les dépôts de "carbone noir" (suies, résidus de la combustion incomplète de carburant tel que le pétrole, le gaz naturel ou le bois) dans le réchauffement climatique de l'Arctique. En effet le "carbone noir", en se déposant sur la neige, en diminue le pouvoir réflectif, et en augmente donc la température. Ceci a notamment pour effet d'accélérer la fonte de ces neiges, ce qui réchauffe davantage le climat local (en diminuant l'albédo terrestre).
     En couplant un modèle qu'ils ont élaboré, le Snow, Ice and Aerosol Radiative (SNICAR, modèle permettant de décrire l'évolution de la neige au cours du temps, notamment sa perte de pouvoir réflectif), avec un modèle de circulation des particules de carbone, les chercheurs ont pu mesurer d'une part la contribution du " carbone noir " et de ses effets sur la neige au forçage climatique et d'autre part la participation des émissions d'origine anthropique à ce type de forçage pour les années 1998 et 2001.
     D'après leur modèle, le "carbone noir" et les mécanismes de rétroaction climatique associés ont augmenté la température moyenne mondiale à la surface du globe de 0.15°C en 1998 et de 0.10°C en 2001 (Dans son 4ème rapport d'évaluation, l'IPCC évalue l'augmentation de la température de surface mondiale au cours des 100 dernières années à 0.8°C). Les températures de l'Arctique, quant à elles, se sont élevées de 1.61°C en 1998 et 0.50°C en 2001. Des feux de forêts importants dans les régions boréales en 1998 sont sans doute à l'origine des disparités entre les deux années. Sur ces deux années les émissions d'origine anthropique sont à l'origine d'au moins 80% du forçage climatique associé au "carbone noir". Limiter les émissions industrielles de suie permettrait de diminuer rapidement le forçage climatique associé au "carbone noir".
Contact:
M. G. Flanner et al., Present-day climate forcing and response from black carbon in snow, Journal of Geophysical Research, 2007, 112(11):
http://dust.ess.uci.edu/ppr/ppr_FZR07.pdf (17 pages )


2) Dirty snow may warm Arctic as much as greenhouse gases

    The global warming debate has focused on carbon dioxide emissions, but scientists at UC Irvine have determined that a lesser-known mechanism dirty snow can explain one-third or more of the Arctic warming primarily attributed to greenhouse gases.
     Snow becomes dirty when soot from tailpipes, smoke stacks and forest fires enters the atmosphere and falls to the ground. Soot-infused snow is darker than natural snow. Dark surfaces absorb sunlight and cause warming, while bright surfaces reflect heat back into space and cause cooling.
     "When we inject dirty particles into the atmosphere and they fall onto snow, the net effect is we warm the polar latitudes," said Charlie Zender, associate professor of Earth system science at UCI and co-author of the study. "Dark soot can heat up quickly. It's like placing tiny toaster ovens into the snow pack."

 The study appears this week in the Journal of Geophysical Research.
     Dirty snow has had a significant impact on climate warming since the Industrial Revolution. In the past 200 years, the Earth has warmed about .8 degree Celsius. Zender, graduate student Mark Flanner, and their colleagues calculated that dirty snow caused the Earth's temperature to rise .1 to .15 degree, or up to 19% of the total warming.
     In the past two centuries, the Arctic has warmed about 1.6 degrees. Dirty snow caused .5 to 1.5 degrees of warming, or up to 94% of the observed change, the scientists determined.
     The amount of warming by dirty snow varied from year to year, with higher temperatures in years with many forest fires. Greenhouse gases, which trap outgoing energy, are primarily responsible for the remaining temperature increase and are considered the Earth's most important overall climate changing mechanism. Other human influences on Arctic climate change are particles in the atmosphere, including soot; clouds; and land use.
     Humans create the majority of airborne soot through industry and fuel combustion, while forest and open-field fires account for the rest. Because of human activity, greenhouse gas levels have increased by one-third in the last two centuries.
     "A one-third change in concentration is huge, yet the Earth has only warmed about .8 degrees because the effect is distributed globally," Zender said. "A small amount of snow impurities in the Arctic have caused a significant temperature response there."
     Previous studies have analyzed dirty snow's effect on climate, but this is the first to take into account realistic emissions from forest fires in the Northern Hemisphere and how warming affects the thickness of the snow pack.
     In some polar areas, impurities in the snow have caused enough melting to expose underlying sea ice or soil that is significantly darker than the snow. The darker surfaces absorb sunlight more rapidly than snow, causing additional warming. This cycle causes temperatures in the polar regions to rise as much as 3 degrees Celsius during some seasons, the scientists say.
     "Once the snow is gone, the soot that caused the snow to melt continues to have an effect because the ground surface is darker and retains more heat," Zender said.
     Dirty snow is prevalent in East Asia, Northern Europe and Northeastern United States.
     Zender believes policymakers could use these research results to develop regulations to mitigate global warming. Limiting industrial soot emissions and switching to cleaner-burning fuels would leave snow brighter, he says. New snow falls each year, and if it contained fewer impurities, the ground would brighten and temperatures would cool. Carbon dioxide lives in the atmosphere for a century, so cutting back on emissions can prevent further warming but does not produce immediate cooling.
 
 
 

     UCI scientist James Randerson and Philip Rasch, a scientist at the National Center for Atmospheric Research in Boulder, Colo., also worked on the study. The National Science Foundation and NASA funded this research.