CLIMATE CHANGE

Nasa took on an unprecedented study of Greenland’s melting. Now, the data are coming in

PUBLISHED : Saturday, 11 February, 2017, 12:59pm
UPDATED : Saturday, 11 February, 2017, 9:27pm

Back in 2015, in a moment of science communication genius, Nasa created a mission called “OMG.” The acronym basically ensured that a new scientific mission – measuring how quickly the Oceans are Melting Greenland – would get maximum press attention.

The subject is actually extremely serious. OMG amounts to a comprehensive attempt, using ships, planes, and other research tools, to understand what’s happening as warm seas creep into large numbers of fjords that serve as avenues into the vast ice sheet – many of which contain large and partly submerged glaciers that are already melting and contributing to sea-level rise.

Greenland is, in fact, the largest global contributor to rising seas – adding around a millimetre per year to the global ocean, Nasa says – and it has 7.36 potential metres to give. The question is how fast it could lose that ice, and over five years, OMG plans to pull in enough data to give the best answer yet.

“We’ve never observed Greenland disappearing before, and that’s what OMG is about,” says Josh Willis, a researcher at Nasa’s Jet Propulsion Laboratory who is the principal investigator on the mission. “We want to watch how it shrinks over the next five years, and see how we can use that information to better predict the future.”

OMG is transforming our knowledge of which glaciers are vulnerable to more warming or not
Mathieu Morlighem, University of California

And now, the first data are coming in, in the form of not one but two new studies published in the journal Oceanography by Nasa scientists and affiliated university researchers, seeking to measure the swirl of oceans around Greenland and in particular how a warm, deep layer of Atlantic-originating water is moving and interacting with its glaciers.

Basically, it works like this: Waters swirl in a broadly clockwise rotation around the enormous island, often darting inward towards the outlying glaciers along the way. And in fjords that are the deepest, the Atlantic layer, which tends to be over 200 metres deep, has the greatest chance of causing sustained melting.

“Where it’s deep, there’s warm water,” says Willis. Above the Atlantic layer, meanwhile, is a layer of colder polar water that has far less of an effect on glaciers – meaning that the big and thick glaciers often get hit hard at their bases, even as the small and thin ones don’t necessarily get hit much at all.

The newly published research does not present any answer – yet – to the big question animating all of this: How fast will Greenland melt and raise seas in a way that threatens, say, Florida?

In order to answer this key question, the researchers need comprehensive data on the depths and shape of the fjords, the thickness of the glaciers, and the behaviour of the oceans around a Greenland coastline that, Nasa notes, is 27,000 miles in length. Then, they will need to feed all of that information into a computer simulation that projects climate change forward to 2100 and calculates the consequences, at a high resolution, for Greenland’s icy coasts.

“It’s too early” to run the model, said Mathieu Morlighem, a researcher at the University of California, Irvine, and the lead author of one of the papers presenting the accumulating data. “I think you need to wait another year or two, maybe more. It was not possible at all before OMG.”

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Still, the recently published findings mark a start. Morlighem’s study, for instance, looked at the depth and shape of the seafloor near the fronts of and beneath numerous Greenland glaciers. The research shows that numerous glaciers extend deeper beneath the surface of the ocean than previously thought.

For instance, Store Glacier in northwestern Greenland (at around 70 degrees North latitude in the image above) starts at 400 metres deep where its front touches the ocean, and then plunges to depths as high as 1,000 metres deep farther inland – making it quite vulnerable to the ocean. Prior research, however, had suggested the glacier was much shallower.

The same was true of numerous other glaciers, which also appear more vulnerable than previously thought.

“OMG is transforming our knowledge of which glaciers are vulnerable to more warming or not,” Morlighem said. “So I wouldn’t say we have been surprised, it’s more, we had no idea, for many of these fjords, what they were looking like.”

Overall, the data are also showing that Greenland’s west coast is far more vulnerable, in general, than its east, Morlighem said.

The second study, meanwhile, examines at ocean circulation around the Greenland coast and finds, strikingly, that between 68 degrees North latitude along the coast and 77 degrees North, the deepest warm layer of Atlantic water cools from 3.5 degrees Celsius down to 2.5 degrees Celsius. Moreover, it does so in part because the water busily melts away at a large and deep glacier called Upernavik at 73 degrees North, which touches the ocean in 675 metre deep waters. The cold meltwater from the glacier spills into the ocean and, through mixing, cools the warm Atlantic water somewhat.

“The glaciers there are actively losing enough ice, and enough fresh water, that it’s important for the oceanography, and how the water changes as it goes up the west coast of Greenland,” says Willis. That in itself is proof that Greenland is melting quite a lot.

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The big picture is that Nasa’s new data suggest – that’s right – new vulnerabilities.

“Overall, together I think these papers suggest that the glaciers as a whole are more vulnerable than we thought they were,” Willis said. He says that, of course, with the aforementioned caveat that Nasa’s not ready yet to feed the data into a model that actually shows how this could play out over the decades of our future.

For now, we’re still stuck with official estimates from bodies like the United Nations’ Intergovernmental Panel on Climate Change, which said in 2013 that Greenland’s melting might at most contribute 21cm to sea-level rise by 2100, with some possible addition from rapid ice collapse (this is the high end number for what scientists call the “likely” range in a worst-case global warming scenario, to be precise). But missions like OMG, in the meantime, are giving us plenty to worry about.

“These kinds of results suggest that we could be in for more sea level rise than we thought,” Willis said. “And we’re not alone, the fact is that almost every time some new results come out of Greenland or Antarctica, we find these glaciers are more vulnerable than we thought.”