Along with the decline in sea ice, the disappearance of ice shelves that are thought to be thousands of years old is rapidly changing the Arctic landscape.

Ice shelves harbor surprisingly diverse collections of organisms in pools of sediment, organisms that might have value as enzymes capable of functioning in extreme cold and harsh light, Mueller said.

They have also acted as a sort of barrier, protecting huge glaciers from exposure to warming waters. Now that the ice shelves are disintegrating, these glaciers -- which are up to 10 kilometers (6 miles) wide -- are thought to be melting more rapidly, and contributing to rising sea levels.

Warmer temperatures in Greenland have led to widespread flooding in the southwest of the island as the ice sheet melts at rates unprecedented in the modern era.

In the Scientific American blog last July, researcher Ben Linhoff wrote: "In the four years our camp has existed on this glacial river, more meltwater is spilling out from beneath Leverett Glacier than we've ever seen."

Were that process to continue or accelerate, many scientists say, the anticipated rise in sea levels over the next few decades may have to be revised upwards.

The National Oceanic and Atmospheric Administration, in its annual Arctic Report Card, published this week, said dramatic melting of the Greenland ice sheet had occurred in July, "covering about 97 percent of the ice sheet on a single day."

Martin Jeffries, co-author of the report, said on the NOAA website: "As the sea ice and snow cover retreat, we're losing bright, highly reflective surfaces, and increasing the area of darker surfaces -- both land and ocean -- exposed to sunlight. This increases the capacity to store heat within the Arctic system, which enables more melting -- a self-reinforcing cycle."

All the evidence says that what in effect is the world's source of air conditioning is getting weaker, with consequences that will be felt far below the 48th parallel.