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Greenland is the largest island in the world and on it rests the largest mass of ice in the northern hemisphere. If all that ice melted, the sea would rise more than 7 meters.
But that’s not going to happen, is it? Well, not anytime soon, but understanding what part of the ice sheet might melt over the next century is a critical and urgent question that scientists are trying to tackle using sophisticated digital models of how the ice cap interacts with the rest of the climate system. .
The problem is that the models are not very good at reproducing recent observations and are limited by our poor knowledge of the detailed topography of the subglacial terrain and the fjords, over which the ice flows.
One way to work around this problem is to see how the ice sheet has responded to climate change in the past and compare it to the model’s projections for the future for similar temperature changes. This is exactly what my colleagues and I did in a new study now published in the journal Communications of nature.
We looked at the three largest glaciers in Greenland and used historical aerial photographs combined with measurements scientists had taken directly over the years to reconstruct how the volume of these glaciers changed during the period 1880 to 2012.
The approach is based on the idea that the past can help inform the future, not only in science but in all aspects of life.
But just like other “classes” in history, the climate and Earth system in the future will not be a carbon copy of the past. Nonetheless, if we determine exactly how sensitive the ice sheet has been to temperature changes over the past century, it may provide a useful guide as to how it will react over the next century.
We found that the three largest glaciers were responsible for 8.1mm of sea level rise, or about 15% of the contribution of the entire ice sheet.
During the period of our study, the sea increased overall by about 20 cm, roughly the height of an A5 booklet, and of this, about the width of a finger is entirely due to the melting ice. of these three glaciers in Greenland.
Melt as usual
So what does this tell us about the future behavior of the ice sheet? In 2013, a modeling study by Faezeh Nick and colleagues also looked at the same ‘big three’ glaciers (Jakobshavn Isbrae in the west of the island and Helheim and Kangerlussuaq in the east) and projected how they would react. in different future climate scenarios.
The most extreme of these scenarios is called RCP8.5 and assumes that economic growth will continue unabated throughout the 21st century, resulting in an average global warming of around 3.7 ° C above current temperatures (around 4 , 8 ° C above pre-industrial or since 1850).
This scenario has sometimes been called Business As Usual (BAU), and there is active debate among climatologists about the plausibility of RCP8.5. Interestingly, however, according to a recent study by a group of American scientists, this could be the most appropriate scenario until at least 2050.
Due to what is called polar amplification, the Arctic will likely warm by more than double the global average, with climate models indicating a warming of about 8.3 ° C in Greenland in the most extreme scenario. , RCP8.5.
Despite this dramatic and terrifying rise in temperature, Faezeh’s modeling study projected that the “big three” would contribute between 9 and 15 mm to sea level rise by 2100, only slightly more than that. that we got from a warming of 1.5 ° C during the 20th century. . How is it possible?
Our conclusion is that the models are faulty, including even the most recent and sophisticated available which are used to assess how the entire ice sheet will respond to the next century of climate change.
These models appear to have a relatively weak link between climate change and melting ice, while our results suggest it is much stronger.
Projections based on these models are therefore likely to underestimate the extent to which the ice sheet will be affected. Other data sources support this conclusion.
What does all this mean? If we continue along this very frightening RCP8.5 trajectory of increasing greenhouse gas emissions, the Greenland ice sheet will most likely begin to melt at rates that we have not seen in at least 130,000. years, with disastrous consequences for sea level and the several million people who live in low coastal areas. 
Jonathan Bamber, Professor of Physical Geography, University of Bristol.
This article is republished from the conversation under a Creative Commons license. Read the original article.
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