OMG, Greenland’s glaciers are melting from below

The outlet glaciers of Greenland’s ice sheet are disappearing at an alarming rate. In fact, they are melting six or seven times faster today than they were 25 years ago. If they were to melt completely, they would raise the world’s sea levels by more than six metres—a distressing figure, considering that a rise of just one centimetre can erode three feet of coastline. But the question that remains unanswered is: Just how fast are they melting?

Over the past six years, JOSH WILLIS and a group of NASA scientists have been working hard to answer this question. Willis started the Oceans Melting Greenland (OMG) project to better to understand what role the Arctic’s warming seas are playing in the melting of Greenland’s outlet glaciers. As he told The Circle, some of their findings were surprising.

When we think of NASA, we don’t usually think about oceans. Why is NASA studying Greenland’s glaciers?

We often think of NASA as the agency looking to the stars. But actually, NASA spends a lot of its time, budget and energy looking at our planet to understand how it is changing. So we have satellites that tell us things like how much ice Greenland is losing, and others that tell us how the sea levels are rising as a result. But until recently, we were missing a piece of the puzzle that has to do with how the oceans are eating away at Greenland’s ice from beneath.

What were you trying to figure out with this project?

Well, we started with this simple science question: “How much are the oceans melting away Greenland’s ice from below?” We know the atmosphere is warming because of human interference with the climate, but the oceans are warming too. As those oceans warm, sea levels rise and interact with ice sheets and glaciers.

When we started OMG, we knew the oceans would probably be important, but we didn’t know how widespread this activity was around Greenland. We came up with this idea to try to measure the oceans all the way around Greenland, then couple those results with measurements of the ice all the way around Greenland. We figured that if we watched the ocean and ice change from one year to the next, over time we would get a sense of how the oceans are affecting the ice.

How did you go about measuring those things and answering that question?

During the summer, sea ice around Greenland retreats and leaves the water open, so we were able to fly over and drop sensors down. We dropped about 250 every year. The sensors fall down through the water, measuring temperature and saltiness as they go, and radio that data back to the airplane. Using these sensors, we were able to map out how the water temperature was changing all the way around Greenland from one year to the next. That was our main tool.

We also flew a radar around the edge of Greenland to measure how the ice was changing. But we needed to understand what role the shape of the sea floor might be playing, so a lot of what we did in the first couple years involved mapping out the sea floor so we knew the pathways where the water could reach the ice.

What were the most significant things you learned in the six years of the project?

Well, one of the real surprises at the very beginning was regarding a glacier called Jakobshavn, which is the biggest in Greenland in terms of how much ice it discharges. This glacier had been steadily retreating for more than 20 years. But when we first started OMG, it suddenly reversed its retreat and started getting thicker.

To understand why, we looked at the oceans first, and it turned out that a sort of temporary cooling signal had made its way up onto the shelf and into the fjord of this glacier. This cooler-than-normal water was enough to reverse the glacier’s retreat temporarily. Since then, the glacier has started to retreat again, and we have observed warmer temperatures. But the fact that the ocean could have such a profound and quick influence on a glacier was a complete surprise to us.

How are you using this information now?

What we really figured out was that understanding the ocean is important if you want to predict what ice sheets and glaciers are going to do. But our ability to predict how fast the ice is going to melt is lagging behind the reality of the melting. What we’re doing now is trying to build some longer-term ocean measurements so people can improve their predictions of the ice melt. We’re also trying to use the information to decide where to keep measuring these ocean waters.

Why should people around the world care how quickly Greenland is melting?

What happens in Greenland doesn’t stay in Greenland: ice loss there affects sea levels and coastlines all around the world. Greenland is now the single largest source of sea-level rise. In just the last 15 or 20 years, it has lost enough ice to raise global sea levels by one centimetre. That may not sound like a lot, but that’s three feet of beach loss on most beaches around the world.