New Study Shows Polar Ice Melting, Sea Levels Rising Due to Global Warming

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NASA Earth Observatory
This 20-mile-long rift on Antarctica’s Pine Island Glacier, seen from a satellite on Oct. 26, will eventually calve off, possibly in the next few months, creating an iceberg the size of New York City. While that won’t raise sea levels since the glacial tongue sits on water, the loss could speed up the flow of ice from Antarctica’s mainland into the sea.

By Glynn Wilson

While there has been little doubt in the science community for the past 20 years about melting polar ice and rising seas due to global warming, a new study just published in the journal Science should put even the most skeptical tea party Republican doubts to rest.

Combining satellite data from dozens of studies, the new study “shows that the Antarctic and Greenland ice sheets have contributed just over 11 millimeters (0.4 inches) to global sea levels since 1992,” according to lead author Andrew Shepherd of the University of Leeds in Britain.

The study also shows that the pace of melting and sea level rise has tripled since the 1990s.

“This improved certainty allows us to say definitively that both Antarctica and Greenland have been losing ice,” Shepherd said.

Two-thirds of this was from Greenland and a third was from Antarctica. That’s 20 percent of all sea level rise over the last two decades, with the rest mostly from thermal expansion of waters due to warming sea temperatures.

In recent years, the percentage “has gone up significantly” to nearly 40 percent, said co-author Michiel van den Broeke from Utrecht University in the Netherlands.

The study was based on input from 47 experts at the 26 institutes that produced earlier studies with some wild variations. Some estimated melt was raising sea levels by up to 2 millimeters a year, others showed gains.

ESA/NASA/Planetary Visions
This chart shows changes in global sea level due to ice sheet melting since 1992. The background image shows thickening (blue) and thinning (red) of Antarctica’s ice sheets over the same period.

Most of the loss is in western Antarctica — at places like Pine Island Glacier, where an iceberg the size of New York City is set to calve off. The iceberg itself won’t raise sea levels since that ice is already atop water, but thinning glaciers mean that ice on the mainland can make its way downhill to the sea faster.

While Eastern Antarctica has added ice, continent-wide over the past decade shows a “50 percent increase in ice loss rate,” said study co-author Erik Ivins, a satellite data expert with NASA’s Jet Propulsion Lab.

Greenland “is losing mass at about five times the rate today as it was in the early 1990s,” Ivins said.

According to the study, Greenland’s melt rate has gone from 55 billion tons a year in the 1990s to nearly 290 billion tons a year recently.

A top ice expert who was not a study co-author told NBC News that the new data mark “an important step forward” in better estimating future sea level rise.

“While we had a basic picture of what was going on, it was an incomplete and blurry one,” said Mark Serreze, director of the National Snow and Ice Data Center at the University of Colorado-Boulder. “We needed to step back and take a fresh look, making the best use of all of the different data sources that we have. With this study we now have a lot confidence in how the ice sheets are behaving.”

The findings come as nations negotiate in Qatar over a new climate treaty to replace the 1997 Kyoto Protocol, which aimed to reduce carbon dioxide and other greenhouse gases tied to a man-made global warming.

And while a half-inch rise in sea levels over 20 years doesn’t sound like much, many experts fear further warming will accelerate the polar ice melt. The ice sheets would raise sea levels by more than 200 feet if they completely melted over centuries. While this is not likely, even a tenth of that would have catastrophic impacts on coastal areas.

The authors warned that while the new data should become the benchmark for future forecasts, any new studies could be compromised if aging satellites are not replaced. In the U.S., the Obama administration is overhauling its satellite program after an outside review team found it “dysfunctional.”

“It’s really critical that these measurements are sustained and several satellites are beginning to fail,” noted Ian Joughin, a University of Washington researcher. “If we really want to have meaningful information that you know planners can use to build seawalls, there’s going to have to be a big push to improve our projections of sea level rise using models.”

© 2012, Glynn Wilson. All rights reserved.

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