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Climate change: ice caps are melting in Greenland – is the tipping point already reached?

Statistical warning signs indicate that the Greenland ice sheet will soon be irreversibly shrinking. Annual fluctuations in the melting of ice in West Greenland have shown signs of a phenomenon known as a “dangerous slowdown,” according to a report by Niklas Poor’s of the Potsdam Institute for Climate Impact Research (PIK) and Martin Rieddel of the University of the Arctic. Norway In Tromso. This statistical specificity indicates that the previously stable state is now unstable and may soon be transformed into a new steady state; Experts also predict such behavior at tipping points in the climate system. The researchers interpret this as an indication that the Greenland ice sheet is approaching a climate tipping point, entering a vicious circle and melting irreversibly.

The cause of the collapse is reactions between the rise of the ice sheet and the loss of ice due to the melting. Below is critical temperature A thin layer of ice loses less mass because it is no longer flowing rapidly; On the contrary, a thick layer of ice is thinned again due to its weight. This means that the ice sheet has a constant elevation in the long term. However, if the temperature rises above a critical value, the melt at the surface of the ice sheet begins to determine the outflow. And as it gets warmer and warmer at lower elevations, the ice sheet is melting faster as it gets thinner – a vicious cycle that only ends when it melts completely.

As the researchers reported in the journal PNAS, the evolution of ice melt over time offers insight into the state of this system even before this vicious cycle begins – if one knows how to interpret the signs. According to Bowers and Ribdell, the Greenland ice sheet is practically in transition between a steady state and a vicious circle. Variation and autocorrelation in data series have increased significantly since the mid-twentieth century. These two statistical parameters act as warning flags.

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Variance describes the size of the bandwidth of the measured values ​​- that is, the variability of the system. Autocorrelation, in turn, shows how similar the system is from one point in time to the next. If both values ​​increase, then the system deviates more and more from the historical norm and at the same time takes longer and longer time to recover from such deviations. This is the essence of “critical slowdown”: as the system approaches a critical transition from one stable system to another, it reacts more and more slowly.

In climate research, such critical transitions are called tipping points. When reached, the system – for example the Greenland ice sheet – does not return to normal after a disturbance, but rather is “upended” to a new stable state. In this case, Greenland is completely free of ice and a sea level rise of about seven meters. The result is consistent with independent predictions based on climate models, according to which the Greenland ice sheet already reaches a critical point when the temperature is less than three degrees above the reference period. It is unclear exactly where this tipping point is located; According to the models, it can reach 1.6 degrees.

Analyzes by Boers and Rypdal now indicate that Greenland is close to irreversible ice loss. Such statistical patterns, originally predicted in theory, appear before critical shifts in many different systems. Biological and technical instability looms, as will climate disruptions. Experts have already found similar signals of “dangerous slowdown” with respect to other sudden climate fluctuations, for example the Dansgaard-Oeschger events during the last ice age.

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Once the ice starts losing, it can happen relatively quickly. According to the simulations, assuming the RCP8.5 pessimistic emission scenario, the ice would have completely disappeared by the year 3000. However, these statements remain fraught with a great deal of uncertainty, since the behavior of the ice caps is largely bewildering. This is why researchers don’t dare to predict how close one really will be to the tipping point and when the vicious circle will start to take hold so noticeably. It is also not known if the ice will actually melt completely – or if there is another steady state of equilibrium with thinner ice. For example, warmer and wetter air can cause more snowfall to compensate for the ice loss. At least if the global temperature does not rise much.