Greenland is the largest island in the world and is home to the largest ice mass in the Northern Hemisphere. If all this ice melted, the sea would rise more than 7 feet.
But that’s not going to happen is it? It won’t be long, but understanding the amount of ice sheet that could melt in the next century is using scientists using sophisticated numerical models of how the ice sheet is trying to cope with the rest of the climate system. The problem is that the models are not so good at reproducing recent observations, and it is limited by poor knowledge of the exact topography of the glacier and fjords beneath the ice.
One way around this problem is to see how the ice sheet has responded to past climate change and to compare it with future model projections for similar temperature changes. That’s what my colleagues and I did in a new study published in the journal Nature Communications.
We studied the three largest glaciers in Greenland and used historical aerial photographs combined with measurements made directly by scientists over the years to reconstruct how the volume of these glaciers changed from 1880 to 2012. The approach is 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 copy of the past. However, if we determine how sensitive the ice sheet has been to temperature changes in the last century, it may be a useful guide on how this will respond in the next century.
We found that the three largest glaciers are responsible for a rise in sea level of 8.1 mm, about 15% of the total ice sheet. During our study, the sea rose about 20 cm around the world, about the height of an A5 booklet, and from there, the width of a finger is roughly because of the melting of ice from these three Greenlandic glaciers.
Melting as usual
What does this mean for us about the future behavior of the ice sheet? In 2013, a model study by Faezeh Nick and colleagues looked at “three” identical glaciers (west of Jakobshavn Isbrae Island and east of Helheim and Kangerlussuaq) and projected how they would respond to different future climate scenarios. The most extreme of these scenarios is called RCP8.5 and economic growth is in the 21st century. It is expected to continue continuously over the century, resulting in an average global warming above current temperatures (about 4.7 ºC above pre-industrial or since 1850).
This scenario has sometimes been called Business As Usual (BAU) and there is active debate among climate researchers about what is credible in RCP8.5. It is interesting to note, however, that according to a recent study by a group of US scientists, at least 2050 may be the most appropriate scenario. Because of something called polar amplification, the Arctic is likely to heat up more than double. overall average, climate models show warming relative to Greenland at around 8.3˚C in the most extreme scenario, RCP8.5.
Despite a dramatic and frightening rise in temperature, Faezeh’s modeling research projected that the “big three” would help raise sea levels by 9 to 15 mm by 2100, slightly more than that achieved by a 20 warmC warming in the twentieth century. How can that be? Our conclusion is that the models are flawed, including the latest and most sophisticated ones that are being used to assess how the entire ice sheet will respond to the next century of climate change. These models seem to have a relatively weak link between climate change and melting ice, when our results suggest that it is much stronger. Projections based on these models therefore predict the impact of the ice sheet. Other lines of evidence support this conclusion.
What does all this mean? If we continue on this daunting RCP8.5 route to increase greenhouse gas emissions, the Greenland ice sheet will begin to melt at rates we haven’t seen in at least 130,000 years, with millions of people living at sea level and in low-lying coastal areas.
Jonathan Bamber, Professor of Physical Geography, University of Bristol
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