The Greenland ice sheet spans about 1.7 million square kilometers in the Arctic. If it were to melt entirely, global sea levels could rise by roughly seven meters, though scientists are still determining how quickly the process would unfold. Recent simulations, which incorporate elements of carbon emission scenarios, suggest that the Greenland melt could reach a point of no return sooner than many expect.
Scientists use tipping-point modeling to describe critical thresholds where a system’s behavior shifts irreversibly. This helps researchers estimate when a major climate transformation, like the Greenland melt, may become unavoidable.
A study based on simulations that include carbon emissions identifies two key tipping points for the Greenland ice sheet: emitting 1,000 gigatons of carbon could trigger melting in the southern portion, while around 2,500 gigatons of carbon would imply the permanent loss of most of the ice sheet.
Half of the first turning point
In current observations, emissions of 500 gigatons have already been released into the atmosphere, placing the system halfway through the first tipping point. This indicates the pathway toward substantial and potentially irreversible changes is already underway.
“The first tipping point is near the present climate state, which means there is real danger of crossing it,” explains a climate scientist from a leading research institute who led the study. “Once the descent begins, it will be hard to reverse.” The findings were published in Geophysical Research Letters.
Greenland’s ice sheet has already been losing mass; estimates show an annual loss of hundreds of billions of tons in the early 2000s, with most decline concentrated in the southern regions. Temperature, ocean currents, precipitation, and other factors collectively influence how fast ice is shed and where the losses occur.
The intricate interplay among these factors, combined with the time horizons scientists must consider when modeling a system as vast as the Greenland ice sheet, makes precise predictions under different climate and carbon-emission scenarios challenging.
Earlier research has identified a global warming range that could push the Greenland ice sheet toward irreversible melt, suggesting a threshold somewhere between one and three degrees Celsius above preindustrial levels.
The disappearance of almost the entire ice sheet
Höning’s new work aims to more comprehensively model how this ice layer responds to climate evolution. The approach began with Earth-system modeling that includes major climate feedbacks alongside ice-sheet dynamics. Initial runs used constant temperature simulations to locate equilibrium states, where ice gain balances ice loss. Scientists then extended to long simulations spanning about 20,000 years with carbon emissions ranging from zero to 4,000 gigatons of carbon.
From these simulations, researchers identified two carbon-tipping points: 1,000 gigatons for significant melting in the southern portion, and 2,500 gigatons for near-total loss of the ice sheet. As melting progresses, the surface lowers, exposing it to warmer air and accelerating the melt.
For the tipping-point feedback to drive a megamelt, global temperatures would need to stay elevated for centuries. A short, two-degree-Celsius rise would not trigger it, but once the threshold is crossed, the process would likely continue regardless of later emissions reductions. Even dramatic decreases in atmospheric carbon dioxide would not permit marked regrowth of the ice sheet.
“Urgent action to reduce emissions is essential. The bulk of the ice sheet’s melting may not occur in the next decade, but it will not be long before the trajectory becomes unstoppable,” the scientist noted.
Reference work: marked citation in scholarly journal Geophysical Research Letters (2022).
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Note on the environment department: [citation attribution withholding for privacy].