Greenland, Antarctic Ice Loss Confirmed in Landmark Study
November 29, 2012
PASADENA, Calif. – An international team of experts supported by NASA and the European Space Agency (ESA) has combined data from multiple satellites and aircraft to produce the most comprehensive and accurate assessment to date of ice sheet losses in Greenland and Antarctica and their contributions to sea level rise.
In a landmark study published Thursday in the journal Science, 47 researchers from 26 laboratories report the combined rate of melting for the ice sheets covering Greenland and Antarctica has increased during the last 20 years. Together, these ice sheets are losing more than three times as much ice each year (equivalent to sea level rise of 0.04 inches or 0.95 millimeters) as they were in the 1990s (equivalent to 0.01 inches or 0.27 millimeters). About two-thirds of the loss is coming from Greenland, with the rest from Antarctica.
This rate of ice sheet losses falls within the range reported in 2007 by the Intergovernmental Panel on Climate Change (IPCC). The spread of estimates in the 2007 IPCC report was so broad, however, it was not clear whether Antarctica was growing or shrinking. The new estimates, which are more than twice as accurate because of the inclusion of more satellite data, confirm both Antarctica and Greenland are losing ice. Combined, melting of these ice sheets contributed 0.44 inches (11.1 millimeters) to global sea levels since 1992. This accounts for one-fifth of all sea level rise over the 20-year survey period. The remainder is caused by the thermal expansion of the warming ocean, melting of mountain glaciers and small Arctic ice caps, and groundwater mining.
“Both ice sheets appear to be losing more ice now than 20 years ago, but the pace of ice loss from Greenland is extraordinary, with nearly a five-fold increase since the mid-1990s,” Ivins said. “In contrast, the overall loss of ice in Antarctica has remained fairly constant, with the data suggesting a 50-percent increase in Antarctic ice loss during the last decade.”
More than 4tn tonnes of ice from Greenland and Antarctica has melted in the past 20 years and flowed into the oceans, pushing up sea levels, according to a study that provides the best measure to date of the effectclimate change is having on the earth’s biggest ice sheets.
The research involved dozens of scientists and 10 satellite missions and presents a disturbing picture of the impact of recent warming at the poles.
The scientists claim the study, published in the journal Science, ends a long-running debate over whether the vast ice sheet covering the Antarctic continent is losing or gaining mass. East Antarctica is gaining some ice, the satellite data shows, but west Antarctica and the Antarctic peninsula is losing twice as much, meaning overall the sheet is melting.
“The estimates are the most reliable to date, and end 20 years of uncertainty of ice mass changes in Antarctica and Greenland,” said study leader, Andrew Shepherd, of Leeds University. “There have been 30 different estimates of the sea level rise contribution of Greenland and Antarctica, ranging from an annual 2mm rise to a 0.4mm fall.
“We can state definitively that both Greenland and Antarctica are losing mass, and as [the] temperature goes up we are going to lose more ice.”
The study shows the melting of the two giant ice sheets has caused the seas to rise by more than 11mm in 20 years. It also found Greenland is losing ice mass at five times the rate of the early 1990s.
The uncertainties over ice cap melting have made it difficult for scientists to predict sea level rise. But Prof Richard Alley, of Penn State University, US, who was not involved in the study, said: “This project is a spectacular achievement. The data will support essential testing of predictive models, and will lead to a better understanding of how sea level change may depend on the human decisions that influence global temperatures.” Rising sea level is one of the greatest long-term threats posed by climate change, threatening low-lying cities and increasing the damage wrought by hurricanes and typhoons.
The results show that the largest ice sheet – that of East Antarctica – has gained mass over the study period of 1992-2011 as increased snowfall added to its volume.
However, Greenland, West Antarctica and the Antarctic Peninsula were all found to be losing mass – and on a scale that more than compensates for East Antarctica’s gain.
The study’s headline conclusion is that the polar ice sheets have overall contributed 11.1mm to sea level rise but with a “give or take” uncertainty of 3.8mm – meaning the contribution could be as little as 7.3mm or as much as 14.9mm.
“We can now say for sure that Antarctica is losing ice and we can see how the rate of loss from Greenland is going up over the same period as well,” he added.
“Prior to now there’d been 30 to 40 different estimates of how the ice sheets are changing, and what we realised was that most people just wanted one number to tell them what the real change was.
“So we’ve brought everybody together to produce a single estimate and it turns out that estimate is two to three times more reliable than the last one.”