NASA scientists say their analysis of new satellite data shows that the Earth lost more than two trillion tons of land ice since 2003.

Measurements of ice collected by NASA's GRACE satellite suggests that most of the land ice lost over the past five years has been in Greenland, with significant losses also occurring in Alaska and the Antarctic. Scientists say the Greenland melt shows no signs of slowing down and, instead, it appears to be accelerating.

Melting of land ice increases sea levels slightly, which also rise as warming water expands.

Scientists say they are concerned about the melting land ice because Greenland didn't add to rising world sea levels in the 1990s. Now, it's adding about half a millimetre of sea level per year.

"It's not getting better. It's continuing to show strong signs of warming and amplification," NASA ice scientist Jay Zwally told The Associated Press. "There's no reversal taking place."

While the figures for the amount of land ice that melted in Greenland this summer aren't complete yet, this year's ice loss won't be as much as 2007, according to NASA. But scientists say it will still be significant.

Melting land ice from Greenland, Antarctica and Alaska raised global sea levels about half-a-centimetre in the past five years, according to NASA scientists.

There was a small glimmer of good news in NASA's latest findings. Land ice in Alaska increased slightly in 2008. The increase was due mainly to increased snowfalls. But NASA notes that since 2003, when the U.S. space agency began collecting satellite measurements, Alaska has lost more than 400 billion tonnes of land ice.

NASA scientists will release their findings on Thursday at the American Geophysical Union conference in San Francisco.

Conference scientists studying sea ice are also expected to announce that parts of the Arctic north were several degrees warmer this past fall.