There is less sea ice in the Arctic than ever before recorded, thanks in part to a warm, sunny summer, a climate scientist said today. And the melting season isn't even over.

On Sunday the sea ice extent was measured at 1.93 million square miles (5.01 million square kilometers).

"It's continuing to go down at a rapid pace," said Mark Serreze, a senior scientist at the National Snow and Ice Data Center in Boulder, Colorado.

The previous minimum record - set on September 21, 2005 - was 2.05 million square miles (5.32 million square kilometers).

©National Snow and Ice Data Center
A new map shows the extent of Arctic sea ice on August 16, 2007, contrasted with the average extent (pink outline) for every August from 1979 to 2000. The current sea ice coverage is the lowest on record, according to the U.S. National Snow and Ice Data Center.

By the end of this summer, scientists at the center say, Arctic sea ice may drop below 1.74 million square miles (4.5 million square kilometers).

Bruno Tremblay is an assistant professor of ocean and atmospheric sciences at McGill University in Montreal, Canada, who is planning a research cruise to the Russian Arctic in September.

In preparation for the trip, he has been observing updated maps of the sea ice extent, which show the quickly melting ice.

"I never thought it would go that low that fast," Tremblay said. "There's still a month of melting in front of us, and we're already past the record of 2005."

Tipping Point?

Sea ice - frozen, floating seawater - melts and refreezes with the seasons, but some of the ice persists year-round in the Arctic.

The current rate of sea ice melt is much faster than predicted by computer models of the global climate system.

Just last year the National Snow and Ice Data Center's Serreze said that the Arctic was "right on schedule" to be completely free of ice by 2070 at the soonest. He now thinks that day may arrive by 2030.

"There's talk of a tipping point, where we thin the ice down sufficiently so that at some point large parts of it can't survive the summer melt season anymore, so we see this very rapid decline in ice cover," he said.

"It's quite conceivable that that tipping point we talk about has already been reached."

Particularly warm and sunny weather in the Arctic this summer has helped speed up the pace of the melt, Serreze said. But the sea ice decline is part of a decades' long trend.

In the dark days of the winter, some sea ice grows back. Overall, however, the ice pack has thinned.

"It's really a reflection of what's been happening over the past 30 years - this general pattern of warming, this general pattern of thinner and thinner ice, which makes it more vulnerable," he said.

Climate Surprise

The loss of sea ice is already having well documented impacts on the Arctic environment, such as shrinking polar bear habitat.

In addition, the melting sea ice will affect atmospheric circulation and precipitation patterns, Serreze said.

"Think of the Arctic as sort of the refrigerator of the Northern Hemisphere climate system. By losing that sea ice, we are greatly altering the efficiency of that refrigerator," he said.

Since different parts of the climate system are integrated, what happens in the Arctic will affect what happens elsewhere on the planet.

However, the climate models disagree on the nature of the potential impacts.

"That's the concern. It's the things that we don't know, it's the climate surprises in store," Serreze said.

If "we lose that sea ice, could we get a climate surprise because of that - a climate surprise that is difficult to deal with, like shifts in precipitation?"