Greenland is dissolving, and a new paradigm suggests that we have greatly underestimated its impact

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 melts, the sea will rise More than 7 meters.

But that won’t happen, is it? Well, not any time soon, but understanding how much ice sheet will melt over the next century is a crucial and urgent question that scientists are trying to address using complex numerical models of how the ice sheet will melt. It interacts with the rest of the climate system.

The problem is that the models are not good at reproducing modern observations and are limited by our poor knowledge of detailed topography of 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 to similar changes in temperature. This is exactly what my colleagues and I did in a new study, now published in the journal Nature Communications.

We looked at the three largest glaciers in Greenland and used historical aerial imagery, along with direct measurements taken by scientists over the years, to reconstruct how the size of these glaciers changed over the period from 1880 to 2012.

This approach is based on the idea that the past can help inform the future, not only in the sciences but in all aspects of life.

But just like other “classes” of history, the climate and Earth system of the future will not be a carbon copy of the past. However, if we discover exactly how sensitive the ice sheet is to temperature changes over the past century, this 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 percent 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, and the ice melt from those three glaciers in Greenland is about the width of a finger.

Melting as usual

So what does that tell us about the future behavior of the ice sheet? In 2013, Prof. Modeling study By Faiza Nick and colleagues, they also looked at the same “Three Great” glaciers (Jakobshavn Isbrae in the west of the island and Helheim and Kangerlussuaq in the east) and predicted how they would respond in different future climate scenarios.

The most of these scenarios are called RCP8.5 It assumes that economic growth will continue unabated through the twenty-first century, leading to an increase in average global warming of about 3.7 ° C above current temperatures (about 4.8 ° C above the pre-industrial era or since 1850).

This scenario has sometimes been referred to as Business As usual (BAU), and there is a Active discussion Climate researchers demonstrate the plausibility of RCP8.5. It is interesting to note, according to a recent study from a group of American scientists, that it may be the most appropriate scenario Until at least 2050.

Because of something called Polar amplification, Arctic temperature is likely to increase by more than twice the global average, with climate models indicating a temperature rise of around 8.3 ° C over Greenland in the most extreme scenario, RCP8.5.

Despite this dramatic and frightening rise in temperature, 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-temperature increase. Degrees Celsius during the twentieth century. . How could it be?

Our conclusion is that the models are wrong, incl The newest and most advanced available That is used to assess how the entire ice sheet will respond to the next century Climate change.

These models appear to have a relatively weak link between climate change and melting ice, when Our results I suggest it is much stronger.

Therefore, projections based on these models are likely not to predict the extent to which the ice sheet will be affected. Other lines of evidence the support this is 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 dire consequences at sea level and Millions of people Living in low-lying coastal areas.

Jonathan BamberProfessor of Physical Geography, University of Bristol.

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