“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.
Source:University of California - Irvine