Greenland is the largest island in the world, and on it rests the largest ice mass in the northern hemisphere. If all that ice melted, the sea would rise by more than 7 meters.
But that’s not going to happen, is it? Well, not any time soon, but understanding how much of the ice sheet could melt in the next century is a critical and pressing question that scientists are trying to tackle using sophisticated numerical models of how the ice sheet interacts with the rest of the the climate system. .
The problem is that the models are not as good at reproducing recent observations and are limited by our poor knowledge of the detailed topography of the subglacial terrain and fjords that the ice flows over and into.
One way around this problem is to see how the ice sheet reacted to climate change in the past and compare it with projections for the future for similar temperature changes. That̵
We looked at the three largest glaciers in Greenland and used historical aerial photography combined with measurements that researchers had taken directly over the years to reconstruct how the volume of these glaciers had changed in 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 like other “classes” in history, the climate and earth system in the future will not be a carbon copy of the past. Nevertheless, if we find out exactly how sensitive the ice sheet has been to temperature changes in the last century, it can provide a useful guide to how it will react in the next century.
We found that the three largest glaciers were responsible for the 8.1 mm rise in sea level, approx. 15 percent of the entire domestic contribution.
During our study period, the sea has risen globally by about 20 cm, approximately the height of an A5 booklet, and hence a finger width is solely thanks to ice melting from the three Greenlandic glaciers.
Melting as usual
So what does that tell us about the future behavior of the ice sheet? In 2013, a modeling study by Faezeh Nick and colleagues also examined the same “big three” glaciers (Jakobshavn Isbrae in the western part 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 through the 21st century, resulting in a global average warming of approx. 3.7 ° C above current temperatures (approx. 4.8 ° C above pre-industrial or since 1850).
This scenario has sometimes been called Business As Usual (BAU), and there is an active debate among climate scientists about how likely RCP8.5 is. However, it is interesting to note that according to a recent study by a group of US researchers, this may be the most appropriate scenario up to at least 2050.
Due to something called polar amplification, the Arctic is likely to heat up by more than double the global average, with climate models indicating around 8.3 ° C warming over Greenland in the most extreme scenario, RCP8.5.
Despite this dramatic and frightening temperature rise, Faezeh’s modeling study expected that the “big three” would contribute between 9 and 15 mm to sea level rise in 2100, only slightly more than what we achieved with a 1.5 ° C warming in the 20th. century. How can it be?
Our conclusion is that the models are flawed, even with the latest and most sophisticated available 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 correlation between climate change and ice melting when our results suggest it is much stronger.
Projections based on these models are therefore likely to underestimate how much the ice sheet will be affected. Other evidence supports this conclusion.
What does all this mean? If we continue along the very frightening RCP8.5 orbit with increasing greenhouse gas emissions, Greenland’s ice tires will very likely begin to melt at speeds we have not seen for at least 130,000 years, with serious consequences for sea levels and many millions of people living in low-lying coastal zones.
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.