Click the image above to view larger image or click here

Links

Read Further

Follow-up Café

Webcast

Related Projects

Sea Ice, the Ocean's Fragile Cloak

Will sea ice modelers soon be out of a job? After stunning sea ice losses last summer in the Arctic, one wonders! By the end of the 2007 summer melt season, the Arctic ice had shrunk by nearly 40 percent from its 1979-2000 average extent, and the fabled Northwest Passage was open to seafarers for the first time in human memory. Sea ice returns during the dark, cold, winter months, but will it recede to yet another record low next year? There are too many competing factors to know for certain, but the likelihood of an ice-free Arctic summer is rising.

The Earth's atmosphere and ocean act as “heat engines,” always trying to restore a temperature balance by transporting heat away from the equator, toward the poles. Arctic sea ice, which covers a huge area---greater than the lower 48 states in summer and twice that in winter---regulates these circulation patterns and therefore our weather. It's disappearance could have significant implications for life on the planet.

Sea ice is simply frozen ocean water. It forms, grows, and melts in the ocean. In contrast, icebergs, glaciers, ice sheets, and ice shelves all originate on land. Sea ice occurs in both the Arctic and Antarctic, growing during the winter months and melting during the summer months, and some sea ice remains all year in both regions. But sea ice is like the snowmen that appear in neighborhood yards after a fresh snowfall---as soon as the temperature rises a tiny bit above freezing, they start to melt and soon are gone!

Ultimately, sunshine is king. It drives the climate system and melts the ice. Its disappearance at high latitudes in the winter allows the ice to grow back. But other factors are at work too, including the sea ice itself. Cold air from Siberia or the Antarctic continent cools the ocean's surface and new sea ice freezes. Winds blow it around, crashing it into the coast or icebergs or other sea ice, causing it to pile up into thick ridges of ice. Ocean currents bring warm waters beneath the ice, melting it from below. Sometimes winds and ocean currents together move the ice into warmer waters, where it melts.

In this tussle between atmosphere and ocean, the sea ice is not a passive bystander. It has its own tactics for meeting the competition or, in some cases, becoming an accomplice to its own destruction. Sea ice is both ocean sunscreen and blanket, preventing solar rays from warming the waters beneath and thwarting ocean heat from escaping to warm the air above. But if gradually warming temperatures melt sea ice over time, fewer bright surfaces are available to reflect sunlight, more heat escapes from the ocean to warm the atmosphere, and the ice melts further. The cycle accelerates. Thus, even a small increase in temperature can lead to greater warming over time, making the polar regions the most sensitive areas to climate change on Earth. But as sea ice melts, it leaves a layer of fresh water at the ocean's surface that inhibits the ocean's global circulation, the "conveyor" that brings warm water toward the poles. Sea ice is both an obstacle and a catalyst for change, able to hasten the pace in either direction.

What happens when there's no more Arctic ice in the summer? Polar bears lose their hunting platforms, for one thing. And they're at the top of the food chain! The web of life will be affected in ways we can not yet imagine, but the news may not be all bad: sea ice in the Antarctic retreats almost completely every summer, supporting a rich ecosystem at whose foundation lie algae and other microbes that thrive in the seasonal ice habitat. Will the Arctic become more like the Antarctic? Stay tuned: some fear the Arctic sea ice has already reached its tipping point.

Links

Read Further | Follow-up Café | Webcast | Related Projects