Greenland’s ice losses have risen to unprecedented levels, scientists say
The Greenland ice sheet’s losses have accelerated so fast since the 1990s it is now shedding more than seven times as much ice each year, according to 89 scientists who use satellites to study the area.
The sheet’s total losses nearly doubled each decade, from 33 billion tons per year in the 1990s to an average now of 254 billion tons annually. Since 1992, nearly four trillion tons of Greenland ice have entered the ocean, the new analysis found, equivalent to roughly a centimetre of global sea-level rise.
While a centimetre may not sound like much, that uptick is already affecting millions.
“Around the planet, just one centimetre of sea-level rise brings another six million people into seasonal, annual floods,” said Andrew Shepherd, a University of Leeds professor who coled the massive collaboration with NASA researcher Erik Ivins.
The results, from a scientific group called the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE), were published Tuesday in the journal Nature.
The research suggests an alarming pace of change for the Earth’s second-largest body of ice, which could theoretically drive more than six metres of sea-level rise over a millennium.
The recent Greenland losses, the experts suggest, match a more dire sea-level projection outlined by the United Nations’ chief climate science body, the Intergovernmental Panel on Climate Change. Under that high-end scenario, Greenland could contribute about 16 centimetres to ocean levels by 2100.
“What that means is that really, the mid-range scenario becomes what was previously the upper scenario, and they will have to invent a new upper scenario, because one currently doesn’t exist,” Shepherd said.
Much more sea-level rise would then come from melting in Antarctica and smaller glaciers around the world, along with the expansion of ocean water that stems from warmer temperatures.
It is not yet clear whether these other components of the sea-level equation are also following the high end, or worstcase, path, however, and the current study was focused only on Greenland. (While Greenland is the biggest contributor to sea-level rise at the present moment, Antarctica ultimately has a larger long-term potential to raise seas.)
Sea-level rise would only continue — and, perhaps, accelerate further — after 2100.
Greenland is the world’s largest island, covered with a continuous sheet of ice produced by many thousands of years of snowfall. The ice sheet’s size rivals that of Alaska, and its centre is well over a mile thick.
The ice flows outward under its own weight toward the ocean, but because of Greenland’s mountainous and rocky coastline, it usually reaches the sea in fingerlike glaciers that extend outward through fjords. These fjords are partially submerged valleys, which were themselves excavated over vast stretches of geological time by the glaciers’ movement.
Several large glaciers account for the biggest ice losses — with Jakobshavn Glacier, in central Greenland, leading the way. But there are hundreds of glaciers overall, and more are losing ice as warming seas come in contact with them through fjords.
The ice sheet itself is also being exposed to warming air temperatures. Most of Greenland has warmed by more than 2 C already, compared with the late 19th century, according to a Washington Post analysis of the globe’s fastest-warming regions. That is double the global average rate of warming.
In summer, these higher temperatures produce more and more meltwater atop the ice sheet, which also runs into the ocean. A little more than half of the Greenland losses have arisen through this process, the study found, which is now happening too quickly to be offset by annual snowfall. The remaining losses are driven by the faster flow of the glaciers out into the deep waters of Greenland’s fjords, where they break off into the ocean in pieces.