The Greenland ice sheet has already reached a tipping point 20 years ago

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 persist 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 was published on August 13, 2020, looking at 40 years of satellite data The earth and the environment of communication. 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. To determine the rate of ice reduction, the authors traced 40 years of satellite data, outlet glacier velocity, thickness, and calving 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 act like spillways on the dam,” he said. “The more you open the spillway… the sooner the reservoirs are pulled down.” This study suggests that long-term thinning in the 20th century, probably due to warming oceans – became 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 retreat at once, it was enough to significantly increase the rate of ice flow in the ocean. It’s like opening the spillway on the dam, “Howet said.

The sea level rise per year as a result of the ice loss shown above is about 0.8 millimeters per year. Deposit: NASA

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 the Antarctic ice sheet), Greenland finds itself in the spotlight. “In terms of direct contributions, Greenland is now truly the largest contributor, with a 20 to 25 percent rise in 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 more than double the annual average. Ian Jafin, Glaciologist And Washington Washington UniversityCenter for Polar Science, connecting the points between these two main studies. He said, “Indeed, no one, 20 years ago, expected glaciers to move as fast as we saw them. 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 ice is poured into the ice sheet and how much is actually melted.” 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, Hawt said, “I think it’s important that this damage to the ice sheet is irreversible. We’ve seen a step-change that isn’t likely to be reversed in the near future, but we still have a long way to go and we still have a lot to say about how quickly the ice sheet will retreat. “

Reference: Michaelia d. King, Ian M. Howat, Salvatore g. Candela, Myong J. Noah, Sengsu Jeong, Bryce PY Noel, Michelle R. “Dynamic Ice Damage from the Greenland Ice Sheet” by Van Dan Brooke, Bert Waters and Adelaide Negret, 13 August Gust 2020, Communications Earth & Environment.
DOI: 10.1038 / s43247-020-0001-2