The reflectivity of snow and ice at the poles, known as the albedo effect, is one of Earth's most important cooling mechanisms. But global warming has reduced this reflectivity drastically, setting off a dangerous warming loop: as more Arctic ice and snow melt, the albedo effect decreases, warming the Arctic further, and melting more ice and snow. The volume of Arctic ice has already shrunk 75% In the past 40 years, and scientists predict that the Arctic Ocean will be completely ice-free during the summer months by the end of the century. Narrated by Richard Gere