Arctic Sea Ice Melt May Set Off Climate Change Cascade

BOULDER, Colorado, March 19, 2007 (ENS) - Arctic sea ice that has been shrinking for decades may have reached a tipping point that could trigger a cascade of climate changes reaching Earth's temperate regions, finds a new study from the University of Colorado at Boulder.

Dr. Mark Serreze, a senior research scientist at CU-Boulder's National Snow and Ice Data Center who led the study synthesizing results from recent research, said Arctic sea ice extent has been decreasing in every month since 1979, when satellite recordkeeping began.

Serreze and his team attributed the loss of ice, about 38,000 square miles annually as measured each September, to rising concentrations of greenhouse gases and strong natural variability in Arctic sea ice.

Dr. Mark Serreze is a research professor of geography with the University of Colorado-Boulder and a senior research scientist with the National Snow and Ice Data Center. (Photo courtesy CU-Boulder)

The review paper by Serreze and Julienne Stroeve of CU-Boulder's NSIDC and Dr. Marika Holland of the National Center for Atmospheric Research titled "Perspectives on the Arctic's Shrinking Sea Ice Cover" appears in the March 16 issue of the journal "Science," published by the American Association for the Advancement of Science.

"Given the growing agreement between models and observations, a transition to a seasonally ice-free Arctic Ocean as the system warms seems increasingly certain," the researchers wrote in "Science."

"The unresolved questions regard when this new Arctic state will be realized, how rapid the transition will be, and what will be the impacts of this new state on the Arctic and the rest of the globe," they wrote.

"We're seeing more melting of multi-year ice in the summer," said Stroeve. "We may soon reach a threshold beyond which the sea ice can no longer recover."

"We have already witnessed major losses in sea ice, but our research suggests that the decrease over the next few decades could be far more dramatic than anything that has happened so far," said Holland. "These changes are surprisingly rapid."

Dr. Marika Holland is a scientist in the Oceanography Section of the National Center for Atmospheric Research. (Photo courtesy UCAR)

Sea ice is frozen seawater that floats on the ocean surface. Covering millions of square miles, sea ice forms and melts with the polar seasons, affecting both human activity and biological habitat.

Arctic sea ice extent is defined as the total area of all regions where ice covers at least 15 percent of the ocean surface.

In the Arctic, some sea ice persists year after year, while almost all Southern Ocean or Antarctic sea ice is "seasonal ice," meaning it melts away and reforms annually. Sea ice in the Arctic appears to play a more crucial role in regulating climate, according to the NSIDC.

Arctic sea ice summer minimum in September 2000, based on simulations produced by the Community Climate System Model. (Image © UCAR)

The decline in Arctic sea ice could impact western states like Colorado by reducing the severity of Arctic cold fronts dropping into the West and reducing snowfall, impacting the ski industry and agriculture, he said.

"Just how things will pan out is unclear, but the bottom line is that Arctic sea ice matters globally," Serreze said.

Passive microwave satellite data reveal that, since 1979, Arctic ice extent has decreased about 3.6 percent per decade, but in recent years, satellite data indicate an even greater reduction in regional ice cover.

In September 2002, sea ice in the Arctic reached a record minimum, according to a 2003 study by Serreze and his team. That year the sea ice extent was four percent lower than any previous September since 1978, and 14 percent lower than the 1979-2000 mean.

In the past, a low ice year would be followed by a rebound to near-normal conditions, but 2002 was followed by two more low-ice years, both of which almost matched the 2002 record.

Arctic sea ice summer minimum in September 2040, based on simulations produced by the Community Climate System Model. (Image © UCAR) (Photo courtesy )