Ice melting faster everywhere.

• Author: Giese, Alexandra
• Position: EYE ON ECOLOGY

FROM THE ARCTIC SEA ICE to the Antarctic interior and the mountainous peaks of Peru, Alaska, and Tibet, ice is melting at an alarming rate. The accelerating loss of ice sheets, sea ice, and glaciers is one of the most powerful and striking indicators of a warming climate. The most notable loss in recent years has been the shrinking of sea ice in the Arctic Ocean. From the beginning of the satellite record in 1979 through 1996, ice area decreased at a steady rate of three percent per decade in response to rising temperature. In the following decade, it decreased by 11%.

Declines in ice thickness and volume are just as dramatic. The combination of these trends has led to a decrease in the amount of ice that persists in the Arctic through multiple seasons. Multiyear ice is more stable and less susceptible to break-up than the thin, short-lived seasonal ice that forms each winter. Since 1987, the amount of ice at least five years old has plummeted from almost 60% to less than 10%. Drastic changes in sea ice cover have led scientists from the University of Washington and the National Oceanic and Atmospheric Administration to predict that we soon could see the first ice-free Arctic in 1,000,000 years.

Declining sea ice is a self-reinforcing trend because of what is known as the albedo effect Ice reflects up to 70% of the sunlight that reaches it, while ocean water reflects six percent and absorbs the rest as heat. This means that, as soon as a small amount of sea ice disappears and exposes the underlying ocean water, the system starts absorbing more energy, which leads to further ice melt. Dangers associated with this runaway warning scenario include rapid destruction of diverse ecosystems that support polar bears, seals, and walruses, among other organisms; a thawing of the Arctic tundra, which can release copious amounts of the greenhouse gas methane; and increased warming of nearby Greenland.

Satellite images and data indicate that the Greenland ice sheet has been experiencing accelerated melt, particularly over the past several decades. In fact, Greenland's average annual melt between 2002-05 was triple that of the 1997-2003 period, and the summer melt area on the ice sheet has increased 30% since 1979. In recent years, changes in ice dynamics associated with higher temperatures have caused glaciers to flow faster, leading to additional ice loss. Melt water lubricates the base of glaciers that carry ice from the interior to the sea, causing...