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Web Feature
The Arctic: Our Global Thermostat
by Maggie Villiger
2 pages: | 1 | 2 |

Duotone landscapeJune 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.

Photo of Sea Ice
The white snow and ice are very reflective, whereas the darker sea water and land readily absorb the sunlight.
 

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.

Image of sunlight reflecting off the ice
 
The more the snow and ice melts, the darker the landscape becomes, and therefore the more sunlight is absorbed.

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. Next Page

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2 pages: | 1 | 2 |

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