Published: Dec. 5, 2012 Updated: 2:49 p.m.

NASA: Polar ice sheets are melting

Ice sheets at both of Earth's poles are melting rapidly, and the rate of loss has increased since the 1990s, a new NASA-sponsored study shows.


Modest warmup after morning clouds

Last large San Onofre part to be shipped out


By PAT BRENNAN / THE ORANGE COUNTY REGISTER

Ice sheets at both of Earth's poles are melting rapidly, and the rate of loss has increased since the 1990s, a new NASA-sponsored study shows.

The study, which combines extensive data from aircraft and satellites, is believed to be the most precise assessment of its kind.

Midnight sun over an iceberg in Disko Bay, Greenland.
IAN JOUGHIN, UNIVERSITY OF WASHINGTON

And it is helping clear up previous confusion about whether Antarctica is gaining or losing ice.

While eastern Antarctica might be increasing its ice mass, ice is being lost in the west and on the Antarctic Peninsula. Overall, both Antarctica in the south and Greenland in the north show a significant loss over the past 20 years.

The Greenland and Antarctic ice sheets combined also are losing more than three times as much ice per year as they were in the 1990s.

Two-thirds of the loss was measured in Greenland, where ice is melting faster, the rest in Antarctica.

Greenland's ice loss, in fact, is five times faster than it was in the mid 1990s, while Antarctica overall has lost ice more steadily, the rate increasing by half over the past 10 years.

And the melting has raised sea levels by nearly half an inch since 1992, scientists estimate – a fifth of global sea level rise during the same period.

"Based upon what we see in Greenland, we might expect to see yet faster ice loss in coming decades," said research scientist Erik Ivins of NASA's Jet Propulsion Laboratory in Pasadena, who helped coordinate the study. "All the data points toward that. For Antarctica, we are less certain."

The study was funded by NASA and the European Space Agency and published last week in the research journal, Science. It involved 47 scientists from 26 laboratories around the world in a collaboration known as the Ice Sheet Mass Balance Inter-comparison Exercise.

Among them were UC Irvine ice experts Eric Rignot and Isabella Velicogna.
Rignot, who has spent years measuring changes in polar ice, said the loss of ice in Greenland is clearly linked to a general warming of the planet over decades.

"In Greenland, we are fairly certain this is the result of warmer air temperature and warmer ocean temperatures," he said.

The situation is a bit more ambiguous, however, in Antarctica. While some influence from planetary warming is likely impinging on the Antarctic continent – mainly shifts in ocean and wind circulation patterns – the continent's relative isolation makes a strong link to global warming elusive.

"Some of what we see is consistent with a warming world, and Antarctica not warming as fast," Rignot said. "But to exactly pinpoint some of the processes along the coast and say this is a direct signature of climate warming is difficult. It will require more studies."

Ivins said warming is likely a significant factor, however, for the Antarctic Peninsula.

"We know we have lost ice shelves" on the peninsula, he said. "That allowed outlet glaciers to speed up, and that's related to global warming."

Data from 10 different satellites were included in the study, among them radar readings of both the height of ice and how fast it flows toward coasts.

Subtle changes in gravity also were measured by NASA's twin GRACE satellites.

Larger or smaller amounts of mass over time show up as gravitational jiggles upward or downward; that can be used to measure thickening or thinning of ice.

The scientists involved in the study recast data they had collected over years to reconcile differences in time periods and geographical areas examined.

"We have these completely independent research groups that went and reanalyzed their data," Ivins said. "We agreed on a time frame, and the space over which to analyze the data, and came up with this level of consistency in the results.

The study also will likely help sharpen the next assessment by the Intergovernmental Panel on Climate Change, the first portion due out next year.

While the study's findings fall within the estimates in the previous assessment, released in 2007, those estimates were not precise enough to reveal whether Antarctic ice was increasing or decreasing.

Contact the writer: 714-796-7865 or pbrennan@ocregister.com.

http://www.ocregister.com/news/ice-379740-antarctica-study.html