The Arctic sea ice is a key indicator of the state of our climate

GreenPeace

The shrinking and receding sea ice has dire consequences. First, as the white ice that normally reflects sunlight away from Earth melts, more of the dark open water of the Arctic Ocean is is exposed, absorbing heat and causing more ice to

melt. This is a positive feedback loop where ice melt causes more ice to melt. Second, distinctive Arctic species such as the polar bear, walrus and ice seals depend on the sea ice; they cannot survive without it, so as the sea ice shrinks and thins, these animals' continued existence is jeopardized, as are the Arctic peoples whose cultures and ways of life have depended on the animals and the ice for millenia.

http://www.greenpeace.org/arctic