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Dirty Snow
Fri Dec 17, 2004
Listen in RealAudio 
As you dust the cobwebs off the old snow shovel, ponder this: these falling flakes
might actually be agents of global warming. Hi, I’m Bryan Yeaton, and this is The
Weather Notebook.
It's not the snowflake itself so much as the hitchhikers that take a ride on it. Black
carbon, also known as soot, has been spewed out for centuries in industrial areas
around the globe. Because snowflakes are so fluffy, they're very adept at picking up
soot particles on their way down. You might not see the gunky stuff, but it's there. A
single large snowflake can catch thousands of bits of dust and soot. Once on the
ground, a soot-filled layer of snow behaves differently than a cleaner one. Even if it's
not obvious to the naked eye, the sooty snow has a slightly dingier color, and this slight
darkening actually helps the sooty snow to melt more quickly because dark surfaces
absorb more sunlight than light-colored ones.
Climate modelers are now taking a closer look at how soot and snow team up. James
Hansen and Larissa Nazarenko, both of NASA, estimate that sooty snow is absorbing
perhaps 3% of the sunlight that would otherwise bounce off more pristine snow across
the Northern Hemisphere. Not only does this absorption help melt the snow sooner,
they say; it also adds to an overall warming of the atmosphere.
Hansen and Nazarenko believe the soot-in-the-snow effect could account for up to a
quarter of global warming observed since 1880. The good news, they say, is that
cutting down on soot emissions would help preserve the planet's fast-melting glaciers
while taking a bite out of global warming at the same time.
Meteorologist Bob Henson brought us today’s story. The Weather Notebook is
supported by Subaru of America, and all of our past show can be found at
www.weathernotebook.org.
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