More than any other place on earth, the poles are feeling the consequences of global warming. The increase in temperature has already altered the formation, thickness, and extent of ice on land and water. Snow reflects sunlight -- which is why it's white. Researchers refer to this surface reflectivity as "albedo" (the term's Latin root, albus, means whiteness). A perfect albedo -- that is, where all radiation from the sun is reflected -- is 1, but as a whole the earth's albedo averages out to 0.31. Climate scientists spend a great deal of time measuring albedo because it's a key indicator of the earth's energy balance.
Since the advent of satellite technology scientists have been able to look down at the earth and take snapshots of the invisible energy radiated and reflected by the earth's surface (the technology is not so different from that of your digital camera). This data is used to create "maps" that show changes in the albedo in different areas.
The farther one travels toward the poles, the greater the consequences of changes in albedo. In the Arctic, for instance, summer is one six-month-long day, during which exposed surface areas are bombarded with sunlight around the clock. When huge masses of ice in the polar oceans break up, water is left exposed. Since the ocean has a lower albedo than the land (it absorbs more radiation), the warming is quicker, the melting more intense. Worse, winds stir the heat into the ocean, and the stored heat seeps beneath the floating ice shelves, attacking them from below. So summer lasts longer, spring comes sooner, and the winter between doesn't last long enough for ice and snow covers to re-form. In the winter of 2004 the Arctic ice pack extended over 15 percent less of the ocean than it did 30 years ago.