Greenland: four times the melting rate

Southwest Greenland melts surprisingly fast and pushes ocean levels up

The loss of ice in Greenland has accelerated - particularly affected is the southwest of the island. © Explora2005 / iStock
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Melting away from the glaciers: The meltdown in Greenland has accelerated - it quadrupled within about ten years, as revealed by a new data analysis. Surprising, however: according to the data, most of the ice thaws in the almost glacier-free southwest. Here the surface ice melts particularly fast. This region could become a major driver of rising sea levels in the future, the researchers warn.

Greenland ice is the second largest ice reservoir in the world after Antarctica. However, due to climate change, glaciers are also shrinking there, and countless pools of meltwater on the ice surface in summer testify to the progressive defrosting of the ice sheet. In the meantime, West Greenland is losing more ice than ever before in the last 450 years and, according to the latest findings, could be more and more sensitive to climate change.

The problem: the increased influx of meltwater into the North Atlantic not only contributes significantly to sea-level rise, it also inhibits thermohaline circulation - the ocean's large circulating current, which is crucial for Europe's climate, among other things.

Ice loss quadrupled in ten years

New data on Greenland's ice shrinkage are now provided by Michael Bevis of Ohio State University and his team. Using data from the GRACE satellite and on-site monitoring stations, they have determined how much ice Greenland lost during the period from 2003 to 2015, and in which regions the melt progresses very fast.

The result: Greenland's ice sheet is losing ground with increasing speed: "At the beginning of 2003, the Greenland ice sheet and its outsourced ice caps lost 102 gigatonnes of ice a year, " the researchers report. "Only ten and a half years later, the rate of ice loss has increased almost fourfold - to 393 gigatons per year." Ad

According to the researchers, at least part of this ice melt could already be irreversible: "We see here an ice sheet approaching the tipping point, " says Bevis. "The only thing we can do here is to adapt and avoid a further increase in global warming."

Big melt off the glacier

Surprisingly, most of the ice was not lost on the great coast glaciers of the southeast and northwest, as expected. Instead, the focus of mass loss was in the southwest of the island. "That can not be explained by glaciers, because there are hardly any there, " says Bevis. "The loss must be due to the loss of surface ice ice, which continues to melt inland."

The researchers assume that the ice sheet Greenland in the southwest from the top defrosts. In summer, only meltwater lakes form, then whole streams of water, which drain the meltwater into the sea. However, this means that southwestern Greenland will contribute more to rising sea levels in the future than previously thought. "That will bring an additional increase in levels, " says Bevis.

Interaction with the North Atlantic Oscillation

However, the new data also shows that the ice melt is not caused solely by the global rise in temperatures. Instead, the Greenland ice sheet is also influenced by the North Atlantic Oscillation (NAO), especially in the southwest. This cyclical fluctuation of the pressure and wind conditions in its negative phase ensures that more warm air reaches West Greenland.

"Since the year 2000, together with global warming, the NAO has strengthened the summer melt, " say Bevis and his colleagues. Although a positive NAO between 2013 and early 2015 led to a slowdown in ice loss. However, climate change is changing the basic conditions to such an extent that in the future this balancing effect will hardly take effect, as the researchers explain.

"In a decade or two, even without the help of the NAO, global warming will lead to melting rates similar to summer 2012, " warn the scientists. As a result, the southwestern part of the Greenland Ice Sheet could become one of the main driving forces for sea-level rise in the future. (Proceedings of the National Academy of Sciences, 2019; doi: 10.1073 / pnas.1806562116)

Everywhere: Ohio State University

- Nadja Podbregar