The polar ice sheets are indeed shrinking—and fast, according to a comprehensive new study on climate change.
And the effects, according to an international team, are equally clear—sea levels are rising faster than predicted, which could bring about disastrous effects for people and wildlife.
Rising seas would increase the risk of catastrophic flooding like that caused by Hurricane Sandy last month in New York and New Jersey. Environmental damage may include widespread erosion, contamination of aquifers and crops, and harm to marine life. And in the long term, rising seas may force hundreds of millions of people who live along the coast to abandon their homes.
By reconciling nearly two decades of often conflicting satellite data into one format—in other words, comparing apples to apples—the new study, published in the journal Science, made a more confident estimate of what's called ice sheet mass balance.
That refers to how much snow is deposited on an ice sheet versus how much is lost, either due to surface melting or ice breaking off glaciers.
Between 1992—when polar satellite measurements began—and 2011, the results show that all of the polar regions except for East Antarctica are losing ice, said study leader Andrew Shepherd, a professor of earth observation at the University of Leeds in the U.K.
In that 20-year span, Greenland lost 152 billion tons a year of ice, West Antarctica lost 65 billion tons a year, the Antarctic Peninsula lost 20 billion tons a year, and East Antarctica gained 14 billion tons a year. (See an interactive map of Antarctica.)
"When we did the experiments properly using the same time periods and same maps, the riddles did all agree," Shepherd said.
According to glaciologist Alexander Robinson, "We've had a good idea of what the ice sheets are doing, but it seems this study really brings it all together in one data set that gives a much clearer picture.
"It's one more piece of supporting evidence that shows there are some dramatic changes happening, and we know that's being driven mainly by a warmer climate and warmer ocean—but there's still a lot we don't know about these regions and how they're changing," said Robinson, of the Complutense University of Madrid in Spain, who was not involved in the research.
(Read "The Big Thaw" in National Geographic magazine.)
For the study, Shepherd and his team took data from three fields of satellite research: Altimetry, which measures the shapes of ice sheets and how they change over time; interferometry, which tracks the speed of ice sheets; and gravimetry, which calculates the weight of ice sheets by measuring Earth's gravitational field.
"Up until now there have been more than 30 studies that have each produced their own estimates of changes in ice sheets," Shepherd said.
"What we did was try to take the strengths of each approach and combined all the satellite technology together to get a better estimate of how ice sheets are changing," he said.
The results are also consistent with observations of climate change at the poles, Shepherd noted ( via news.nationalgeographic.com ).