The Ice Albedo Feedback Loop

Another important feedback loop is called the ice albedo effect. As noted above, albedo is the ability of a substance or a body to reflect sunlight. Ice and snow are white, which means that they reflect the sun's rays—or, to put it another way, they have very high albedos. In fact, according to geographer Grant R. Bigg, ice and snow have "the highest albedos of almost any natural sur-face."10 From 70 percent to 80 percent of the sunlight that strikes ice and snow is reflected back into space.

ARCTIC SEA ICE EXTENT

The graph shows the area of ocean with at least 15% sea ice over the course of 2007 and the average for 1979-2000. It also shows sea ice for 2009 up to October, when the graph was made.

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Source: ""Arctic Sea Ice Extent,"" National Snow and Ice Data Center, October 12, 2009. http://inside.org.

The ice albedo effect is most important at the poles where large expanses of ice and snow reflect sunlight and help to keep the climate cold. Because of the ice albedo effect, relatively small shifts in temperature at the poles may cause major climactic fluctuations. For instance, some scientists believe that in the past when temperatures dropped, it created more ice cover, which reflected more sunlight, lowering temperatures even further. There was a period 800 million years ago, in particular, when some scientists believe that runaway ice albedo feedback was responsible for a remarkable period of cooling, during which ice formed all over the globe, even near the equator.

With global warming, the earth may be set to experience a feedback loop of the opposite kind. As the earth's temperature starts to rise, ice and snow at the poles will start to melt. Land and water have a much lower albedo than ice: for example, ocean water reflects less than 10 percent of the sunlight that strikes it. As more sunlight is absorbed, temperatures increase—which, in turn, melts more ice and further increases the temperature.

Scientists worry that ice albedo feedback is in part responsible for the fact that summer sea ice in the Arctic has fallen by about 386,102 square miles (about one million square kilometers) in the past 30 years. Environmental education specialist Lisa Gardiner has noted that "According to climate models, the pace of ice melt will continue to quicken so much that that there may be no more summer sea ice within the next few decades."11

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