NASA data shows thickest and oldest Arctic ice is melting

Thickness is an indicator of long-term health of sea ice, and that's not looking good at the moment," Walt Meier of the National Snow and Ice Data Center told reporters in a telephone briefing.

This adds to the litany of disturbing news about Arctic sea ice, which has been retreating over the last three decades, especially last year, when it ebbed to its lowest level.

Scientists have said the trend is spurred by human-generated climate change.

Melting Arctic ice does not raise sea levels as the melting of glaciers on Greenland or Antarctica could, but it does contribute to global warming when reflective white ice is replaced by dark water that absorbs the sun's heat.

Using satellites that measure how much ice covers water in the Arctic and Antarctic, Meier and other climate scientists found a steep drop in the amount of perennial ice -- the hardy, thick ice that is over a year old -- in the north.

The oldest Arctic ice that has survived six years or more is the toughest, and even that shrank dramatically, Meier and the other scientists said.