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Could targeted geoengineering cut sea-level rise?

28 Mar 2018
Michael Wolovick

Targeted geoengineering to preserve continental ice sheets deserves serious research and investment, according to a comment in Nature.

“We understand the hesitancy to interfere with glaciers – as glaciologists, we know the pristine beauty of these places,” wrote John Moore of Beijing Normal University, China, and the University of Lapland, Finland, and colleagues. “But we have also stood on ice shelves that are now open ocean.”

The researchers propose stalling the fastest flows of ice into the oceans to buy a few centuries to deal with climate change and protect coasts. The ice sheets of Greenland and Antarctica will contribute more to sea-level rise this century than any other source, they say.

“There is going to be some sea-level rise in the 21st century, but most models say that the ice sheets won’t begin collapsing in earnest until the 22nd or 23rd centuries,” added team member Michael Wolovick of Princeton University, US, in a press release. “I believe that what happens in the 22nd or 23rd centuries matters. I want our species and our civilization to last as long as possible, and that means that we need to make plans for the long term.”

There are three potential ways to slow glaciers in these sheets: preventing warm ocean waters from reaching their bases; buttressing the ice shelves where they start to float with artificial islands in the sea; and drying glacier beds by draining or freezing the thin film of water they slide on.

“Many of the most important outlet glaciers in Greenland are about 5 km wide, and there are bridges that are longer than [that],” said Wolovick. “The important ice streams in Antarctica are wider, tens of kilometres up to 100 km, but their societal consequences are larger as well, because they could potentially trigger a runaway marine ice sheet collapse. The fast-flowing parts of the ice sheets – the outlet glaciers and ice streams – might be the highest-leverage points in the whole climate system.”

Engineers have already constructed artificial islands and drained water beneath a glacier in Norway to feed a hydropower plant, according to the press release. Raising a berm in front of the fastest-flowing glacier in Greenland – constructing an underwater wall 3 miles (4.8 km) long and 350 feet (107 m) high in Arctic waters – would be a comparable challenge, and could cost billions of dollars

Without coastal protection, the global cost of damages from sea-level rise could reach $50 trillion a year, the team wrote. And the sea walls and flood defences necessary to prevent those damages would cost tens of billions of dollars a year to build and maintain. Glacial geoengineering has potential risks, especially to local ecosystems, and the glaciers and their outflow channels need to be more precisely mapped and modelled, according to the team. What’s more, glacial geoengineering is not a substitute for climate mitigation through emissions reductions.

“Glacial geoengineering will not be able to save the ice sheets in the long run if the climate continues to warm,” Wolovick said. “In the long run, there are two possible routes that glacial geoengineering could take: on the one hand, it could be a stopgap solution meant to preserve the ice sheets until the climate cools enough that they are once again viable on their own; on the other hand, it could be a managed collapse meant to keep the rate of sea-level rise down while slowly letting the ice sheet waste away.”

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