Sea Ice
Sea ice covers an area of almost 16 million square kilometers of the Arctic seas during its maximum extent in winter.Each summer the pack ice (Arctic ice cover)melts and shrinks in area,and,at a minimum,extends over about 9 million square kilometers.The sea ice is an important part of the climate of the Arctic,and indeed of the whole world,because it has a large effect on the way the surface of the Arctic is heated.Sea ice is highly reflective-we see this by the need to wear sunglasses when walking over snow or ice.Water,on the other hand,appears rather dark by comparison.Where sea ice covers the Arctic seas,much radiation from the Sun is reflected back into the atmosphere.However,where open water is present,most of that radiation is absorbed and acts to heat the water.As the water heats up,more ice can be melted,and so on.This is called a positive feedback effect and is one of the key reasons why scientists are monitoring both the extent and the thickness of Arctic sea ice today.If sea ice covers a progressively smaller part of the Arctic seas in a world that may be affected by greenhouse gases,then this positive feedback could be critical to the rate at which our planet warms up.
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