Caspar Haarloev from "Into the Ice" documentary via Reuters
The Greenland ice sheet is melting seven times faster than it was in 1992 — an increase that's even greater than scientists expected.
According to a new study, Greenland has lost more than 4.2 trillion tons of ice in the last quarter-century, which raised global sea levels 0.4 inches.
Greenland's ice sheet is losing ice seven times faster than it was in 1992 — a rate that tracks with one of the worst-case scenarios predicted by climate scientists.
According to a study published today in the journal Nature, Greenland has lost more than 4.2 trillion tons of ice since 1992. That's roughly the amount of water in Lake Michigan, or the equivalent of 1.5 billion Olympic-sized swimming pools.
This melting in Greenland has already raised seas by 0.4 inches since 1992. If the current melt rate continues, Greenland will add another 2.75 inches to global sea levels by 2100, according to Andrew Shepherd, the lead author of the study. That means more people living in coastal areas will be at risk of flooding from sea level-rise.
"The most surprising aspect by far is that the increased sea-level rise, which may seem small to most people but is enough to cause an extra 40 million people to experience annual floods," Shepherd told Business Insider. "Small changes in sea-level rise do matter."
On track for a worst-case scenario
Ian Joughin, University of Washington
Roughly 656,000 square miles in size, the Greenland ice sheet covers an area almost three times that of Texas. Together with Antarctica's ice sheet, it contains more than 99% of the world's fresh water.
Most of that water is frozen in masses of ice and snow that can be up to 10,000 feet thick. But as greenhouse gases build up in the atmosphere, the oceans absorb 93% of the excess heat those gases trap. The warming air and water are leading ice sheets to melt at unprecedented rates.
For the new study, almost 100 polar scientists used satellite data to produce the most complete picture of Greenland ice loss to date. They documented changes in the ice sheet's volume and in the flow of melted water into the ocean between 1992 and 2018.
The results showed that the rate of ice loss in Greenland has increased from 36 billion tons per year in the 1990s to 280 billion tons per year in the last decade — a seven-fold increase.
A study published earlier this year offered similar findings: Those scientists calculated that the current rate of Greenland's ice loss is six times faster than the rate four decades ago.
The new study also found that Greenland's ice loss peaked in 2011, when the sheet sloughed off 369 billion tons of ice — 10 times the annual average melt rate in the 1990s — during a period of intense melting.
Yearly ice loss has since dropped to an average of 262 billions tons, though Shepherd and his co-authors noted that this average does not include 2019's unusually hot summer.
A summer of excess melting
The ominous news about Greenland comes in the wake of another worrisome finding: Antarctica's melting is also speeding up. In the 1980s, Antarctica lost 40 billion tons of ice annually. In the last decade, that number jumped to an average of 252 billion tons per year — just a hair behind Greenland's new average.
The biggest difference between the Greenland and Antarctic ice sheets is that the latter is less impacted by seasonal melting that's driven by global warming, Shepherd said. In the Arctic, meanwhile, summer melting makes it harder for scientists to anticipate what the Greenland melt rate will be in a given year. (Melting season runs from June through August, with peak melting in July.)
"In Greenland, accounting for weather is a challenge too, as hot summers like 2012 and 2019 are difficult to predict as they are elsewhere on the planet," Shepherd added.
This summer, extreme melting followed the hottest month ever recorded (July), as an intense heat wave hit Europe then wafted over to Greenland. From July 30 to August 3, melting occurred across 90% of the continent's surface, dumping 55 billion tons of water over five days. That's enough to cover Florida in almost 5 inches of water. On August 1, Greenland's ice sheet lost 12.5 billions tons of ice, more than any day since researchers started recording ice loss in 1950.
NASA via Associated Press
Scientists didn't expect to see Greenland melt at this rate for another 50 years: By the last week of July, the melting had reached levels that scientists with the United Nations' Intergovernmental Panel on Climate Change (IPCC) had projected for the year 2070, in the most pessimistic scenario.
400 million people may be at risk of coastal flooding by 2100
The IPCC has estimated that global sea levels could rise by 2 feet (60 centimeters) by 2100, putting 360 million people at risk of annual coastal flooding. But the new study shows that if Greenland's current trend continues, seas would rise 2.75 inches more than the IPCC's prediction — which would put an additional 40 million people at risk.
"As a rule of thumb, for every centimeter rise in global sea level, another 6 million people are exposed to coastal flooding around the planet," Shepherd said in a press release.
Ian Joughin, University of Washington
He added: "These are not unlikely events or small impacts; they are happening and will be devastating for coastal communities."
Read the original article on Insider