In 2005, the ice cap covering the Arctic Ocean shrank to its smallest size since researchers began keeping records a century ago. In the past five years, scientists reported that many Greenland glaciers are sliding faster to the sea and melting at their edges. Climate simulations indicate that the buildup of greenhouse gases in the atmosphere will accelerate melting. Are these temporary phenomena or the first hints of long-term climate change? The answers are critical because the Arctic will not just feel the impacts of climate change, it will also cause a cascade of other global changes. As the Arctic goes, most scientists say, so goes the planet.