New satellite data released by U.S. government scientists indicate no let-up in a 10-year warming trend that is shrinking and thinning the Arctic sea ice surrounding the Earth's North Pole.

NASA satellite data shows the maximum Arctic sea ice cover for 2008-09 as the fifth lowest in six years

The U.S. space agency NASA and the National Snow and Ice Data Center in Boulder, Colorado, have been monitoring Arctic sea ice from space since 1979. Center research scientist Walt Meier says the last six years have shown the lowest Arctic sea ice cover on record. He says this year's cover is shaping up to be the fifth lowest ever.

"We used to have an amount of winter ice cover at the maximum that was about twice the size of the lower 48 United States, and at 5.85 square miles, we are about 278,000 square miles less than we were during the 1979 to 2000 average."

That, Meier says, is now about the size of the state of Texas.

The extent of sea ice cover and its thickness are measures of the health of the Arctic. Meier says the older, thicker ice is melting away and being replaced by newer, thinner ice.

"In terms of the thickest ice and the oldest - or greater than two years old - that's been on a pretty big decline over the last couple years."

During the winter, winds and currents push some of the thick, multi-year ice out of the Arctic Ocean. In the past, that thicker ice was replenished by new ice that survived several summer melt seasons

Meier adds that it is the lowest ever at the end of the winter season, just under 10 percent - down from 40 to 50 percent in the 1980s and 1990s.

"We are getting an ice cover as we finish the winter and head into the summer that is much more vulnerable to the summer melt and much more likely to melt more completely and expose that dark ocean," he says.

Arctic sea ice works like an air conditioner for the global climate system. It naturally cools air and water and reflects solar radiation back into space. Meier says a warmer Arctic and thinner sea ice cap changes the balance between the normally cold Arctic and warmer lower latitudes.

"That contrast between the cold pole and the warm equatorial regions and lower latitudes is one of the things that sets up your circulation patterns, your winds, your ocean circulation and essentially your weather patterns, and so all of those things are subject to change as the ice cover changes."

Changes to the ice cover, Meier says, also impact Arctic wildlife and the people who depend on the frozen ecosystem.

"There are also very big implications for shipping through the Arctic and opening up commercial shipping lanes potentially and extraction of natural resources."

Meier says competition for those resources, as countries move in to stake out claims in the newly unfrozen north, could threaten global security.