When islands in the Pacific sink into rising seas or their residents have to build ever higher dikes to protect themselves, it has a lot to do with Greenland. The island has been losing ice for a long time, An average of 270 billion tons have melted away every year since 2002 or broken off in the form of icebergs. Greenland is causing sea levels to rise by 0.8 millimeters every year, which accounts for a fifth of the total increase. And it could be much more: if the entire Greenland ice sheet melted away, sea levels worldwide would rise by around seven meters.
It is therefore important for coastal regions to know how quickly the ice in Greenland thaws. And when, due to rising temperatures, a “tipping point” is reached at which a complete loss of the ice sheet could no longer be stopped. Researchers led by Nils Bochow from the Arctic University of Norway in Tromsø have now tried to answer this question. In the specialist magazine Nature Calculate, how the ice sheet could develop depending on how high temperatures rise as a result of climate change. And whether humanity would have a chance to reverse this development.
The scientists focused on scenarios in which humanity fails to limit the global temperature increase to 1.5 degrees. Exceeding this mark could potentially be fatal for the Greenland ice sheet, as researchers’ simulations show. According to the pessimistic scenario, the tipping point from which there is a risk of “abrupt loss” of the ice sheet would already be reached at 1.7 degrees of global warming. In the more optimistic model, the ice only thaws completely from a global temperature increase of 2.3 degrees. The earth has currently heated up by around 1.1 degrees compared to pre-industrial times.
In order to stabilize the Greenland ice cream, global temperatures would have to fall again from 2100 onwards
In any case, it would take several thousand years for the Greenland ice to completely thaw. But that would have serious consequences much earlier; Already in the coming centuries there would possibly be a rise in sea level of the order of one meter or more – this does not even take into account the contributions from the rest of the Arctic and the Antarctic.
Nevertheless, according to the researchers, the inertia of the Greenland ice masses offers the chance of preventing complete melting, even if there is a significant increase in temperature in the meantime. In order to do this, however, it would have to get colder again in the foreseeable future – for example by reforesting large areas of land in order to bind carbon dioxide (CO₂), or by removing the greenhouse gas directly from the atmosphere using huge filters.
Bochow’s researchers do not consider how useful such an approach would be. All they are interested in is what such climate stabilization would mean for Greenland. According to the calculations, it doesn’t look so bad. If the temperature increase can be reduced to 1.5 degrees by the year 2200, the Greenland ice sheet would remain stable in the long term and the sea level would rise by less than a meter due to Greenland meltwater. Even if the climate takes a millennium to stabilize, sea levels would not rise by more than two meters, no matter how high temperatures climb by the year 2100.
Uta Krebs-Kanzow from the Alfred Wegener Institute for Polar and Marine Research (AWI) in Bremerhaven also confirms that a global reduction in temperature could stabilize the Greenland ice sheet. “In principle, this is conceivable as long as the temperature trend reverses before the ice sheet has lost too much mass,” says the climate researcher. On a “healthy ice sheet” there are regions at high altitudes where snow slowly accumulates, which stimulates ice formation. However, a feedback effect could prevent regeneration, Krebs-Kanzow points out: If ice melts away at the edges, snow slides in from higher up and the ice sheet flattens. Since it is now lower overall, less snow forms inside – even when it gets colder again. What is therefore important is “the detailed timeline of possible future scenarios”.
In addition, a significant increase in temperature in the meantime would have other serious consequences, such as more extreme weather. It is also uncertain whether the melting processes in Greenland can be adequately depicted with current means. “The ice sheet models have significant weaknesses, especially when it comes to interaction with the oceans,” says Mojib Latif, climate researcher at the Helmholtz Center for Ocean Research Kiel (Geomar). But so far we have to rely on them, “because there are almost no measurements, especially from inside the ice.”
The researchers led by Nils Bochow admit that some factors are difficult to assess. It is uncertain how climate change will affect the Gulf Stream and what that means for Greenland. In addition, the Arctic is currently warming much faster than the rest of the globe. If this trend worsens, Greenland could thaw sooner than expected. But one thing is virtually certain: over the course of this century, the shrinking Greenland ice will continue to cause the sea to swell. According to in the specialist magazine Nature Climate Change published study A further increase of at least 21 centimeters is practically inevitable, no matter how ambitious climate protection becomes in the future. Or as polar researcher Jason Briner from Buffalo University in New York puts it: “Our fate and that of the Greenland ice sheet are closely linked.”