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Greenland Ice Sheet: The largest unknown in climate science



JON GERTNER: One major challenge for scientists involved in climate change was the quest to find out if these large ice sheets, these ancient remnants of the Ice Age in Greenland and the Antarctic, are shrinking or growing. And we are used to it, I think now to read all the news that Greenland loses ice and the Antarctic melts and this glacier seems to be unstable. But that was really a kind of epic discovery of how to do it. Many of the ways we've found that out are satellites and other types of airborne observation instruments, such as airplanes. For example, laser altimeters that read the ice by emitting laser shocks and trying to measure the decrease in the height of the ice. And at least in Greenland, we've noticed that this ice sheet has been losing ground since the early 1

990s.

The ice in Greenland, the frosting on the cupcake, moves slowly into the ocean. And it moves into the ocean in two ways: it melts on the surface in summer, and then you see those beautiful azure pearls of lakes on the surface, which eventually flow into the ocean and meltwater rivers. It also has these glaciers on the edges that reach into the ocean, and they erode as these huge icebergs, which in turn swim away and also melt. And all that raises the sea level.

The larger picture is that our sea level is currently rising by about three millimeters per year, which is actually a pretty small amount. And the reasons why it melts are that with the warming of the earth there is a so-called thermal expansion, which means that the oceans literally expand, just as hot water expands, [it] gets bigger and higher. The other reason is that in the Himalayas, in Canada and Alaska there are mountain glaciers worldwide which also drain into the water and make a contribution. And the third reason is that Greenland and the Antarctic lose ice, both by the melting of the surface of Greenland and by these glaciers, which break off into icebergs and raise the sea level.

At present, Greenland's contribution is one millimeter per year. And we could perhaps put that aside and say that one millimeter a year is not very much, but that is accelerating. What we also know is that things do not necessarily move linearly with ice sheets. Much in the science of glaciology and ice cover is quite new. It's not like we could go back 100 years and try to figure it out – or at that point we knew how ice sheets work. In fact, we can now look at an ice sheet in Greenland or the Antarctic, for example in the West Antarctic, and we know that no one has ever seen what we see now. No one has ever experienced the collapse of an ice sheet. Nothing in recorded history explains how an ice sheet collapses in warmer temperatures.

So we are in this place where we know that the climate is warming dramatically. We know that the ice sheets become more unstable at warmer temperatures. We know that they have weak spots. We also do not know exactly how the physics of large ice sheets work. And we're trying to create models, scientists are trying to make models, but these models are not necessarily as good as some other models, predicting future temperatures, for example. We've heard that if the Earth throws so much CO2 into the air, we'll warm the atmosphere by 2 or 3 degrees – that's pretty much proven. But if we try to model an ice sheet and say that Greenland will lose so many tons of ice by the year 2050 or become the Antarctic, we are not sure. I mean, sometimes we're not sure because we do not know if people can actually stop burning so many fossil fuels and if we can change the way we heat up. But we also can not know it, because the glaciers can rise and slow down. You can pause if they hit bumps before they break into the sea. Greenland can fluctuate or it can get cold.

We now know that Greenland loses between 250 and 300 billion tons of ice per year. In recent years, it has lost more than a trillion tons of ice. It's a huge amount. It is getting bigger. We can not stop thinking of this place, or we should not stop thinking of that place, even though it seems almost as far removed from our imagination. If you live in New York, London or Los Angeles, it seems so incredibly far away. And yet, this ice-covered island could to a certain extent determine our future, in the sense that it will raise the sea level. The ice that falls into the ocean can alter the circulation pattern of the ocean, which can have enormous effects on temperature and sea level. And then there are many other surprises that we may not yet understand just because we are actually witnessing something we have never seen before.


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