The new method showed more
Previous studies have used computer models of the island’s ice sheet behavior to estimate future losses, but the physical processes are complex, so results varied widely between models, and the estimates were therefore highly uncertain.
But now the authors of the work published in the journal Nature Climate Change used real satellite images that tracked the loss of ice in Greenland and also the shape of the glacier on its surface in the years 2000-2019. This data allowed them to calculate how much the equilibrium state changes, where the loss of ice caused by natural melting in the summer months is balanced by snowfall. This then made it possible to calculate how much ice has already disappeared, how much will disappear and how great its overall stability is.
“It’s a very conservative estimate, where we were rather at the lower end of what’s possible,” said Professor Jason Box from the Danish National Geological Survey, who led the research.
The estimate of 27 centimeters is therefore minimal, as it only takes into account the effect of global warming itself, but does not address, for example, how the glacier collapses at the edges. The authors are aware of this weakness—they cite the study’s main strength as providing a solid estimate of inevitable sea-level rise.
This method is also unable to tell how quickly the change will occur, but according to the authors, it is not really that important. “Whether it comes in 100 years or 150 years, it will come.”
According to Colgan, however, it can be seen that human behavior changes can change a lot. “If 2012 becomes normal, then the water level will rise by at least 78 centimeters, which is a huge number. But the difference between 78 and 27 centimeters is a good indication of the difference that can be achieved through the implementation of the Paris Agreement. There is still a lot of room for damage minimization.”
At the same time, the new estimate is significantly higher than scientists had predicted: a report last year by the Intergovernmental Panel on Climate Change projected a likely rise in sea level due to the melting of Greenland ice in the range of six to thirteen centimeters by 2100.
But it’s not just Greenland’s glaciers that are hiding, another ice sheet that was part of the land surface is also disappearing. For example, the mountain glaciers in the Himalayas are threatened with a decline of about one-third by the end of the century, and those of the Alps even by about half. And also, according to some studies, the West Antarctic ice sheet is already past the point where large losses are inevitable. The fact that warmer water has a larger volume also contributes to the rise of sea levels.
“There is a growing consensus in the scientific literature that there will be a rise of several meters over the next 100 to 200 years,” Colgan pointed out. The collapse of the East Antarctic ice sheet, which would lead to a 52-metre rise in sea levels within a millennium if it were to melt entirely, could be averted if climate action is taken quickly, a scientist says.