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Since 1998, there have been at least 29 estimates of ice sheet losses
based on various satellite techniques. However, even though they were
often looking at the same satellite findings, researchers could not agree on
how to interpret the data.
The last major assessment in 2007 by the International Panel on
Climate Change was so broad it was impossible to say whether the
Antarctic ice sheets were growing or shrinking.
In the new study, 47 researchers from 26 laboratories around the
world reconciled the differences by combining measurements collected by
different types of satellites and matching time periods and survey areas.
That produced estimates believed to be more than twice as accurate as
those in the 2007 IPCC report.
The researchers estimate that between 1992 and 2011, the Greenland
ice sheet lost 2,940 gigatonnes of ice and ice sheets in Antarctica lost
1,320 gigatonnes. (One gigatonne equals one billion tonnes.)
Results in the Antarctic varied by region. The Western Antarctic and
Antarctic Peninsula both lost ice during the study period, but ice sheets in
the Eastern Antarctic — which occupies more than three-quarters of the
continent — actually grew in size during the final years of the survey.
Milne said the ice losses are significant because of their impact on
sea levels. “When you talk about millimetres per year, people don’t really
understand how much ice that actually is,” he said. About 360 gigatonnes
of ice must melt to raise worldwide sea levels by one millimetre, he said.
The geological record indicates that ice sheet losses generated annual
sea level rises in excess of 10 millimetres a year during past periods of
climatic change, the study says.
“The prospect of such changes in the future are of greatest concern.
Even the modest rises in ocean temperatures that are predicted over the
coming century could trigger significant ice sheet mass loss through
enhanced melting of ice shelves and outlet glaciers.”
According to the 2006 Stern Review on the Economics of Climate
Change, 200 million people live in coastal flood plains and assets worth
$1 trillion lie within a metre of the current sea level.