By Alister Doyle, Elizabeth Culliford and Lucas Jackson
Flying over eastern Greenland, the NASA scientists stared down from a Gulfstream jet as it followed the precise course they had flown in previous years – using radar to map the loss of ice
“In the tube,” flight engineer David Elliott said as the team locked into their route over the ice sheet covering 80 percent of the world’s largest island. Out the window, massive chunks of broken ice looked like salt flakes on the water.
The March mission was part of NASA’s Oceans Melting Greenland (OMG) project, a five-year, $30 million (22.8 million pounds) effort aimed at improving sea level rise projections by understanding how warming oceans are melting ice sheets from below – the most ambitious research on the subject to date.
Rising seas threaten low-lying cities, islands and industries worldwide. But projections for how high and how soon the rise will come vary wildly in part because scientists lack clarity on how fast warming oceans are melting polar ice sheets. The uncertainty confounds the preparations of governments and businesses and fuels the arguments of climate-change sceptics.
A draft report by the United Nations’ Intergovernmental Panel on Climate Change (IPCC), for example, predicts that seas are likely to rise between 33 centimetres and 1.33 meters by 2100 – a wider range than the 28-to-98 centimetres estimate in the last IPCC assessment from 2013.
The IPCC projections, which were reviewed by Reuters, have not been previously reported.
Until now, most glacier research has focussed on how warming air melts ice sheets, but warming oceans play a crucial role, said OMG’s principal investigator, Josh Willis.
“It’s not just an ice cube and a hair dryer,” he said, offering an oft-used metaphor for how warmer air melts glaciers
“We’re really just beginning to grapple with how these ice sheets are going to behave in a warming world.”
The OMG project aims to clarify how Greenland itself contributes to rising seas, but also to apply that knowledge to the study of the much larger region of Antarctica, which has far more ice and could ultimately play a much bigger role in sea-level rise. And while most of Greenland’s ice is on land above sea level, large parts of the Western Antarctic ice sheet are below sea level, making them more vulnerable to warming oceans.
Melting ice in Greenland currently adds 0.8 millimetres of water to global ocean levels annually, more than any other region, according to NASA. That’s enough water to fill 115 million Olympic-sized swimming pools.
Scientists authoring the IPCC study, expected to be the most authoritative sea-level assessment to date, declined to discuss the preliminary findings on the record. Hans-Otto Poertner, a leader of the IPCC report, said the document will be “subject to review and further revision” before its planned release in September 2019.
The forecast range for sea-level rise, however, is unlikely to get more precise, one scientist working on the draft said on condition of anonymity.
“The range for sea level rise is getting wider,” the scientist said.
HOLES IN THE DATA
Better projections would be invaluable to governments worldwide. Britain’s Environment Agency, for instance, foresees upgrades to a barrier on the Thames River to protect London against 90 centimetres of sea level rise by 2100, but could modify the plans to account for a catastrophic 2.7 meters.
One 2017 study published by U.S. scientists in a journal of the American Geophysical Union estimated a rise of 50 centimetres by 2100 would submerge land that is now home to about 90 million people, mainly in China, Vietnam and Bangladesh. A rate of 1.5 meters would swamp the homes of more than 150 million people worldwide, the study estimated.
A 2016 study published in a journal of the U.S. National Academy of Sciences predicted that an event comparable to Superstorm Sandy, which flooded large swaths of the New York region in 2012, would be up to 17 times more likely by 2100 if seas rise by 1 metre.
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