Jonathan Bamber, University of Bristol
Greenland is the largest island in the world and is located on it by the largest ice mass in the Northern Hemisphere. If all this ice melted, the sea would rise by more than 7 meters.
But that won’t happen, is it? Well, not any time soon, but understanding how much of the ice sheet might melt in the next century is a crucial and urgent question that scientists are trying to address using complex numerical models of how the ice sheet interacts with the rest of the climate system. The problem is that the models are not good at reproducing recent observations and are limited by our poor knowledge of detailed topography of the terrain and subglacial fjords, into which the ice flows.
One way to solve this problem is to see how the ice sheet responded to changes in climate in the past and compare it with models’ projections of the future for similar changes in temperature. This is exactly what my colleagues and I did in a new study, now published in Nature Communications.
We looked at the three largest glaciers in Greenland and used historical aerial imagery, along with measurements taken directly by scientists over the years, to reconstruct how the size of these glaciers changed during the period from 1880 to 2012. The approach was based on the idea that the past could help In informing the future, not only in science but in all aspects of life. But just like other “categories” of history, the climate and Earth system of the future will not be a carbon copy of the past. However, if we find out exactly how sensitive the ice sheet was to temperature changes over the past century, it could provide a useful clue as to how it will respond over the next century.
We found that the three largest glaciers were responsible for 8.1 mm of sea level rise, which is about 15% of the contribution of the entire ice sheet. During our study period, the sea rose globally by about 20 cm, about the height of an A5 brochure, thanks to the melting of ice from those three glaciers in Greenland.
Melting as usual
So what does that tell us about the future behavior of the ice sheet? In 2013, a modeling study by Faiza Nick and colleagues also looked at the same “Big Three” glaciers (Jakobshavn Isbrae in the west of the island and Hillheim and Kangarlussuaq in the east) and predicted how they would respond in different future climate scenarios. The most extreme of these scenarios is called RCP8.5 and it assumes that economic growth will continue unabated through the twenty-first century, causing global average temperatures to rise by about 3.7 ° C above current temperatures (about 4.8 ° C above pre-industrial or Since 1850.).
This scenario has sometimes been referred to as “business as usual” (BAU) and there is an active debate among climate researchers about the plausibility of RCP8.5. It is interesting, however, to note that according to a recent study from a group of American scientists, the most favorable scenario might be until at least 2050. Due to something called polar amplification, the Arctic temperature is likely to be more than twice the global average, with climate models indicating a temperature of around 8.3 ° C over Greenland in the most extreme scenario, RCP8.5.
Despite this dramatic and frightening temperature rise, Fayez’s modeling study predicted that the “Big Three” would contribute between 9 and 15 mm to sea level rise by 2100, slightly more than what we got from a 1.5-degree temperature rise. Celsius during the twentieth century. How could it be? Our conclusion is that the models are flawed, even including the newest and most advanced ones being 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, when our results indicate that they are much stronger. It is therefore possible that projections based on these models do not predict the extent to which the ice sheet will be affected. Other lines of evidence support this conclusion.
What does it all mean? If we continue along the extremely dreaded RCP8.5 path of increased greenhouse gas emissions, it is very likely that the Greenland ice sheet will begin to melt at rates not seen in at least 130,000 years, with disastrous consequences at sea level and for the millions of people who live in Low-lying 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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