News in Science

Greenland ice melt accelerating

Cold confirmation Greenland has had an average net loss of 200 million tonnes of ice every year since 2003, confirm scientists who are studying the changing mass of the island using satellite data.

The latest analysis backs up the previously reported trend without even including the last two summers of record-breaking ice melts.

"Greenland is really the place where everyone agrees that (the ice melt) is definitely accelerating with time and there is a big contribution to sea level rise," says researcher Isabella Velicogna of the University of California at Irvine (UCI).

Velicogna is an expert at analysing the same kind of data used in this most recent study: from the Gravity Recovery and Climate Experiment (GRACE) which can detect mass changes on the surface of the Earth over time.

GRACE does this by detecting subtle increases and decreases in gravity, which is directly related to the mass below the two orbiting GRACE satellites.

Just how much is 200 million tonnes of ice? Roughly, it's the amount needed to fill enough railroad coal cars to encircle the Earth.

In the latest work, Princeton University researcher Chris Harig and Frederik Simons applied a new method to analysing the GRACE data. They found that during 2003 and 2004, mass loss was centred along the eastern coast of Greenland.

From 2005 to 2006 mass loss dropped in the northeast but rose in the southeast. Meanwhile, more mass was lost along the northwest coast, especially from 2007-2010.

They published the results of their work in this week's issue of Proceedings of the National Academy of Sciences.

"The study confirms what we already knew," says Eric Rignot, an Earth Systems Science Professor at UCI and scientist at NASA's Jet Propulsion Lab. "The authors use a new decomposition, but the sources of error and corrections are essentially the same as for other studies."

"The main message from this work is that we are doing a much better job figuring out where the mass is melting," says Harig.

Mystery over inland increase

The new study also confirms that the mass of central Greenland is slowly and slightly increasing, which Harig and Simons attribute to a possible increase in snowfall there.

But Rignot and Velicogna disagree that more precipitation is the cause.

"The claim that the mass increase in central Greenland reveals an increase in precipitation in Greenland as expected in a warming climate is incorrect," says Rignot.

"Precipitation in Greenland is more complex and is concentrated along the coastal sectors. So the changes observed in central Greenland are insignificant in terms of total precipitation. Regional climate atmospheric models, in fact, do not show any change in total precipitation in Greenland over the last few decades."

Whatever the reason, the take home message is that the, the small amount of increase detected in central Greenland is not remotely enough to offset the melting along the coasts, says Velicogna.