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 June
15 , 2004 — As
Alan Alda traveled around the state of Alaska, he saw the
effects of climate change happening right now. Lots of scientists
told him that the Arctic is the proverbial canary in the coal
mine when it comes to global warming. Here's why..
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The
Ice-Albedo Effect
The
Arctic is a unique landscape, covered by snow and ice for
much of the year. And paradoxical as it may seem, it's precisely
this frozen quality that helps make it more susceptible to
warming.
Snow
and ice are white and very reflective. They have what scientists
call a very high albedo - that's a measure of how much light
a surface reflects. Between 70 and 80 percent of the sun's
rays that hit this kind of frozen surface are bounced right
back out into space. So the land or water beneath the snowy
blanket doesn't get a chance to absorb much of that solar
radiation.
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The
white snow and ice are very reflective, whereas the
darker sea water and land readily absorb the sunlight.
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Now
imagine that a little bit of heat is added to the system.
That's exactly what is happening in the real world; scientists
say that the average temperature in Alaska has risen 4 degrees
Fahrenheit since the 1950s. With warmer temperatures, some
of the snow and ice melts, exposing the darker land or water
underneath. These surfaces have much lower albedos - open
water reflects less than 10 percent of the solar energy that
hits it, for example. So more heat is absorbed by the landscape.
Then
a feedback loop kicks in. More heat is absorbed by the darker
surface, so more snow and ice melt. More of the darker surface
is exposed, leading to the absorption of even more heat, more
snow and ice melt, and so on. Just a small temperature rise
can set this feedback cycle into motion. The opposite effect
is possible too; a small temperature decrease would lead to
more snow and ice, would lead to more solar radiation being
bounced back to space, would lead to colder temperatures,
would lead to more snow and ice, and so on. Scientists describe
the onset of past ice ages in this way.
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The
more the snow and ice melts, the darker the landscape
becomes, and therefore the more sunlight is absorbed.
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The
very fact that the Arctic is frozen a good part of the year
makes it fragile and easy to be drastically affected by global
warming. Adding freshwater to the oceans as it melts from
glaciers on the land surface will change the salinity of the
seas, which can affect global ocean circulation patterns.
Ecosystems are very different when frozen or thawed. Current
conditions in many parts of the Arctic are fairly waterlogged,
with water held close to the surface of the land. That's because
just below ground level lies frozen soil, the so-called permafrost
layer. But as permafrost thaws, water drains more easily and
the landscape becomes more productive. The treeline migrates
northward. As temperatures warm, the undecomposed peat in
the landscape will begin to breakdown and emit the carbon
that has been locked in the ground for millennia. It's another
feedback system; warming will lead to increased levels of
carbon dioxide reaching the atmosphere where it can act as
a greenhouse gas and lead to more warming. The cycle is complex,
though, and scientists aren't sure how the variety of factors
involved will interact. 
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