Greenland’s ice sheet reached a tipping point 20 years ago, a new study finds.

At the end of the 21st century, unknown to the world, the Greenland ice sheet has entered a state of potential mass damage that will last for the foreseeable future, according to a new study. However, the discovery raises concerns about the future of ice sheets, although scientists stress that reducing emissions is critical.

The study, which looked at 40 years of satellite data, was published in Communications Earth and the Environment on August 13. Second only to the size of the Antarctic ice sheet, the Greenland ice sheet covers about 80 percent of the vast island. It has a global average sea level rise of about 24 feet and, due to its rapid retreat, is considered to be one of the largest contributors to rising sea levels worldwide.

The decline in ice fall has been well documented over the past two decades, while a recent study led by Bird Polar and Michaelia King of the Climate Research Center found that moving ice sheets out of equilibrium in unbalanced conditions helped wider glacial retreat. This work suggests that if the oceans and atmosphere stopped warming today, the ice sheet would lose more ice than that.

In the decades leading up to the turn of the century, the ice sheet was in a state of relative equilibrium. The snow lost in a given year will be replenished by snowfall during the winter, and the sheet retains the near mass. But in the early 2000s, outward currents in the ocean began to outpace the annual snowfall caused by outlet glaciers, which, in a balanced year, would replenish lost ice. The authors tracked 40 years of satellite data to determine the rate of ice reduction, tracking the outlet glacier velocity, thickness, and calibration front position. The shift they found represents a tipping point that is unlikely to be reversed in the near future. “It’s like a gear change … we’ve accelerated the gutters on the edge of the ice sheet, and now… we expect a lot of damage to the ice sheet in the near future,” King told GlacierHub.

Ian Howt, director of the Byrd Polar and Climate Research Center and co-author of the paper, explained to GlacierHub that the dynamics of ice loss through outlet glaciers can be compared to the operation of a dam. “Those glaciers behave like spillways on the dam,” he said. “The more spillways you open … the faster the reservoir goes to the bottom.” The study suggests that long-term thinning in the 20th century, probably due to warming oceans – was a mass retreat in the early 2000s. The result was a “step increase” in discharge rates through outlet glaciers; Prior to 2000, 420 gigatonnes of ice was released annually. In subsequent years, the rate of discharge per year increased to 480 gigatonnes. One gigaton is equivalent to one billion metric tons, almost all geological mammals on earth (excluding humans). “When all these glaciers retreated at the same time, it was enough to significantly increase the rate at which ice is coming into the ocean. It’s like opening the spillway over the dam,” Howette said.

According to King, the significance of this new dissolution rate is that “more ice is constantly being lost in the flow of these glaciers than is gained by the accumulation of ice.” An additional 60 gigatonnes of snowfall or reduced melting will be needed each year to return to a balanced state. However, under all climate change scenarios, the opposite is expected.

The findings of this study – along with others that document the decline of the Greenland ice sheet – spell out worrying news for the rising sea level. Marco Tedesco, a professor of marine geology and geophysics at the Lamont-Doherty Earth Observatory, explained to GlacierHub that Greenland has been a sheet of ice, and that it will contribute to rising sea levels. The two primary causes of sea surface surges are thermal expansion – sea water expands as it warms and ground-based ice melts. With rising sea levels drowning 150 million people permanently below the ected high tide line (and that estimate assumes the stability of a sheet of Antarctic ice), Greenland finds itself in the spotlight. “In terms of direct contributions, Greenland is now truly the largest contributor, with a rise of about 20 to 25 percent of sea level due to Greenland,” Tedesco said. Also, the percentage of contributions could rise to 30 or 40 percent by the end of the century, according to Tedesco.

Another study on the Greenland ice sheet, backed by Tedesco, recently made international headlines, concluding that 2019 was a year of record ice losses. According to scientists, the amount of snow lost in 2003 was twice the annual average compared to 2003. Ian Jaufin, a glaciologist at the University of Washington’s Polar Science Center in Washington, D.C., connects the points between the two large studies. “Indeed, some 20 years ago, glaciers that we didn’t expect to move as fast as we saw them,” he told Glacier Hub. In terms of the annual loss of ice, “people think of it as melting, but it’s basically a balance between how much snow falls each year, and how much snow melts and how much it melts in the ice sheet.” Eventually, melting or dissolving ice alone will not explain the changing ice sheet. Instead, in a complex dynamic it is the two processes that glaciologists run to understand using a combination of field work, remote sensing and modeling.

Rapid international action is needed to limit global warming to 1.5˚C, which will give more time to adapt to rising sea levels. Addressing the recent headlines announcing that the ice sheet has reached a point of return, Hawte said, “I feel emphatic that this damage to the ice sheet is irreversible. We have seen a step-change that is unlikely to be reversed in the near future, but we still have a long way to go and we have yet to say how quickly the ice sheet will retreat. ”

This story is republished courtesy of the Earth Institute, Columbia University http://blogs.ei.columbia.edu.