Global warming and the consequent sea level rise have been major environmental concerns for many years now. A new study, published in the journal Nature Communications, adds to the worries by revealing that Greenland’s largest glaciers could lose even more ice than previously predicted. This could have huge consequences for the rate of global sea level rise.
An ice sheet is a mass of glacial land ice extending more than 50,000sq km. The two ice sheets on Earth today cover most of Greenland and Antarctica. Together, the Antarctic and Greenland ice sheets contain more than 99% of the freshwater ice on Earth. The Antarctic Ice Sheet extends almost 14mn sq km. The Antarctic Ice Sheet contains 30mn cu km of ice. The Greenland Ice Sheet, which extends about 1.7mn sq km, covering most of the island, is already melting rapidly, and ice loss is one of the main contributors to rising sea levels. Planet-heating greenhouse gas emissions like carbon dioxide are accelerating this melt.
But experts have less information on how these vital glaciers have changed in the past, particularly in the centuries before satellite records existed. Understanding how glaciers have responded to past changes in climate can impact projections scientists make about how they may respond to future warming.
The new study has filled in some of those gaps. The researchers found that Greenland’s glaciers are very sensitive to climate conditions, and have lost ice in the late-19th and early-20th century at rates that rival or surpass those seen today. With the planet – and the Arctic in particular – expected to warm much more this century, the scientists warn their findings show that ice loss on Greenland could exceed even the worst-case projections.
David Holland, a professor of mathematics and environmental science at New York University and a co-author of the study, said the team’s findings show that the Arctic “is undergoing a one-two punch with respect to the loss of its land and sea ice covers in a warming world.”
Using historical photographs of the Jakobshavn, Helheim and Kangerlussuaq glaciers, which hold enough ice to raise global sea levels by roughly 1.3m, the team calculated ice loss from 1880 to 2012. They estimated that the amount of ice lost from these three glaciers alone resulted in a sea level rise of 8.1mm. Holland said that while the three glaciers are important in their own right, they also serve as proxies for the majority of the other outlet glaciers in Greenland, giving scientists a glimpse at how the entire ice sheet, which is constantly shifting and moving, behaves. If the interior of the ice sheet is considered as a mountain lake, these outlet glaciers are the streams fanning out from the lake, carrying ice away from it and in many cases, into the ocean. When ice breaks off from the glacier and lands in the ocean, it raises sea levels.
Ice loss over time is driven by natural shifts in winds and ocean currents, and when warm waters get near the glaciers, they melt. But human-caused warming has altered the climate and is changing how the winds and ocean interact with the ice sheet, and therefore influencing the amount of ice loss.
Rising seas are already causing problems in many low-lying coastal areas. And for places like New York and Shanghai, 1m or more of sea level rise could spell disaster. Another recent study found that rising seas could cost the global economy $14.2tn in lost or damaged assets by the end of the century, and expose as many as 287mn people to episodic flooding, up from 171mn today.
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