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Climate-induced melt of Greenland ice will cause 10-plus inches of sea-level rise

Ten inches is a conservative estimate. Greenland icemelt could raise sea levels by 31 inches — and it's already too late to stop it from happening.

(CN) — No matter what, it is too late to stop Greenland from losing trillions of tons of ice.

William Colgan realized this back in 2017, when he wrote a paper describing Greenland’s ice loss in terms of teratonnes, the equivalent of one trillion metric tons. “That was when the cumulative mass loss that we had been observed graduated beyond gigatonnes (or billions of tonnes),” wrote the senior researcher from the Geological Survey of Denmark and Greenland (GEUS) via email.

According to their study published in Nature Climate Change, Colgan along with Jason Box and other colleagues studied the Arctic’s climate between 2000 to 2019 and the imbalance it created in the Greenland ice sheet.

To do that, the researchers did not use models due to the inaccurate prediction of Greenland’s response to climate change. According to the study, models struggle with imprecise measurements of land, atmosphere, and ocean boundaries, such as inaccurate models of ice flow and climate interaction.

“Trying to boil down the entire climate system, including the Greenland ice sheet, into discrete equations is tricky business,” wrote Colgan. “You’re bound to omit some processes or perhaps mis-formulate other processes. Then you need to see how this system of equations describing the ice sheet behaves under what we call boundary conditions or forcings, that means things like ocean and atmospheric temperatures in contact with the ice sheet. Although we have the best generation of process-level ice sheet models to date, there is clearly room for improvement, since so many conditions and equations need to be prescribed.”

So they took their own measurements. Using satellites and the authors’ own observations from nearly 20 years of research, the glaciologists project that in the next century the Greenland ice sheet will lose about 110 trillion tons of ice leading to an average global sea level rise of at least 10.63 inches. Per the study, the researchers calculated the low estimate for ice loss is 3.3%

“It is a very conservative rock-bottom minimum,” Box said. He elaborated that this figure will likely more than double within the 21st century. “In the foreseeable scenario that global warming will only continue, the contribution of the Greenland Ice Sheet to sea level rise will only continue increasing. When we take the extreme melt year 2012 and take it as a hypothetical average constant climate later this century, the committed mass loss from the Greenland Ice Sheet more than doubles to 78 cm (30.71 inches).”

An example is the change in the ice sheet's so-called snow line, a boundary between areas of the ice sheet exposed to net melting during summertime and the areas without exposure. Normally, the upper layer of winter snow does not melt but remains on top to nourish the ice sheet, even during the summer. At most, the study says, a hot summer would move the boundary further up the ice sheet.

The researchers say they found climate change caused layers of snow to melt without regaining an equal or greater amount of snow in return. As a result, it created a mass budget deficit, or disequilibrium, that no one can fully reverse. Perhaps only mitigate its effects.

“Simply put,” wrote Colgan, “if we stop climate change now, under a low emissions Paris Agreement type climate scenario, we hold Greenland’s contribution to 274 mm. If we proceed down the road of a high emissions business-as-usual climate scenario, it seems quite possible that we will commit the ice sheet to 782 mm (approximately three times more) of sea-level rise.”

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