Sufficiently fast reversal of global warming may prevent tipping of the Greenland ice sheet

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Bringing temperatures back closer to pre-industrial levels sufficiently fast may prevent tipping of the Greenland ice sheet and avoid drastic sea level rise even if critical temperature thresholds are crossed temporarily, a study finds

Crossing critical temperature thresholds of the Greenland ice sheet due to anthropogenic global warming might be reversible for hundreds of years without triggering a large-scale tipping event. This means that we likely still have time to avoid a full meltdown with the ensuing sea level rise if actions are taken quickly. That is the conclusion from a simulation study by Nils Bochow, University of Tromsø, Norway, et al. The calculations indicate that even if the global mean temperatures peak at 6 degrees above preindustrial levels by 2100, a subsequent cooling would – if fast enough – prevent a complete collapse of the ice sheet and consecutive sea level rise.

The authors caution, however, that their results are based on a limited set of runs of two ice sheet models that disregard how the concerted global climate change influences the Arctic climate apart from temperatures and precipitation.

Time to act

”We wanted to investigate how the Greenland ice sheet might react over centuries to millennia to the drastic, yet so far comparably still short-lived warming of our time. Our results show that we can likely avoid a full Greenland ice sheet tipping if we act fast enough to reduce greenhouse gas emissions.” says co-author Niklas Boers from the Technical University of Munich and the Potsdam Institute for Climate Impact Research, Germany.

”What we find suggests that even if we do not manage to stay below 1.5 or 2 degrees of global warming, and even if we temporarily cross the critical temperature threshold of the Greenland ice sheet, we still have a chance to act,” says Nils Bochow, University of Tromsø, Norway.

A range of experiments

The team of climate scientists conducted a range of experiments with two independent ice sheet models.

In each run, global mean temperatures rose to up to 6 degrees above pre-industrial levels until the year 2100. After this, temperatures were again gradually reduced over different time ranges, from 100 to 10,000 years. Such a cooling mimics a possible restoration of the climate system by CO2-sequestering, which essentially means collecting carbon from the atmosphere and storing it safely, for example by large-scale reforestation.

The experiments identified a number of steps, determined by threshold temperatures where the ice sheet will tip and eventually collapse completely if global warming is not reversed.

However, the calculations also revealed that the ice sheet reacts so slowly to anthropogenic warming that reversing the current warming trend within centuries may prevent it from tipping at all.

Safe under 1,7 degrees

Additionally, the experiments suggest that 1,7 degrees is a safe limit, under which the Greenland ice sheet will not tip according to the employed model, and will contribute only little to sea level rise even over 100,000 years.

All in all, 2,850,000 cubic kilometers of ice turns out to have a lot of inertia.

The authors warn, however, that essentially all other sub-elements of the climate system react faster to global warming than an ice sheet. These include rainforests, wind and precipitation patterns, or ocean current systems, which all change or even commit to abrupt, irreversible changes on significantly shorter time scales, leading to much shorter windows of opportunity to avoid tipping.

”And even when avoiding large-scale tipping of the Greenland ice sheet, temporary sea-level rise can be substantial and the higher temperatures rise, the more difficult it will be to bring them down to safe levels in the long term,” says Niklas Boers.

”Our results certainly do not imply we should not do anything before the year 2100. I definitely think it is not the responsibility of the next generation to fix what we or prior generations messed up. The Greenland ice sheet is just a small part of the picture and there are many other negative consequences related to anthropogenic climate change that we might face if we don’t act in time.,” says Bochow.