“Geoengineering interventions can be targeted at specific negative consequences of climate change, rather than at the entire planet,” postdoctoral research associate in Atmospheric and Oceanic Sciences Michael Wolovick said.
The ice sheets of Greenland and Antarctica will contribute more to sea-level rise this century than any other source, so stalling the fastest flows of ice into the oceans would buy us a few centuries to deal with climate change and protect coasts, say the authors.
“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,” said Wolovick. “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.”
Stalling the fastest flows of ice into the oceans would buy us a few centuries to deal with climate change and protect coasts, argue John C. Moore and colleagues.
The glaciers could be slowed in three ways: warm ocean waters could be prevented from reaching their bases and accelerating melting; the ice shelves where they start to float could be buttressed by building artificial islands in the sea; and the glacier beds could be dried by draining or freezing the thin film of water they slide on.
The engineering costs and scales of these projects are comparable with today’s large civil engineering projects, but with extra challenges due to the remote and harsh polar environment. Engineers have already constructed artificial islands and drained water beneath a glacier in Norway to feed a hydropower plant. Raising a berm in front of the fastest-flowing glacier in Greenland — constructing an underwater wall 3 miles long and 350 feet high in arctic waters — would be a comparable challenge.
A polar geoengineering project would easily run into the billions of dollars, but without coastal protection, the global cost of damages could reach $50 trillion a year. In the absence of geoengineering, the sea walls and flood defenses necessary to prevent those damages would cost tens of billions of dollars a year to build and maintain.
Three ways to delay the loss of ice sheets<.b>
1. Block warm water
The Jakobshavn glacier in western Greenland is one of the fastest-moving ice masses on Earth. It contributes more to sea-level rise than any other glacier in the Northern Hemisphere. Ice loss from Jakobshavn explains around 4% of twentieth-century sea-level rise, or about 0.06 millimeters per year.
Jakobshavn is retreating at its front. Relatively warm water from the Atlantic is flowing over a shallow sill (300 metres deep) and eating away at the glacier’s base. Making the sill shallower would reduce the volume of warm water and slow the melting. More sea ice would form. Icebergs would lodge on the sill and prop up the glacier.
A 100-metre-high wall with sloping sides of 15–45° could be built across the 5-kilometre fjord in front of Jakobshavn glacier by dredging around 0.1 cubic kilometres of gravel and sand from Greenland’s continental shelf (see ‘Glacial geoengineering’). This artificial embankment, or berm, could be clad in concrete to stop it being eroded. The scale of the berm would be comparable with large civil-engineering projects. For example, ten times more material — 1 cubic kilometre — was excavated to build the Suez Canal. Hong Kong’s airport required around 0.3 cubic kilometres of landfill. The Three Gorges Dam used 0.028 cubic kilometers of cast concrete.
2. Support ice shelves
Where Antarctica’s ice sheets reach the sea, ice flows out as floating shelves. Pinned by rocks and islands, these platforms hold back the glaciers and limit how much ice reaches the sea. As the air and ocean around Antarctica warm, some ice shelves are becoming thinner, particularly those fringing the Amundsen Sea. In 2002, scientists were shocked at the collapse of 3,200 square kilometres of the Larsen B ice shelf, which is now only 30% of the size it was during the 1980s7. Half a dozen other shelves around the Antarctic Peninsula have shattered in the past 30 years.
3. Dry subglacial streams
Fast-sliding ice streams supply 90% of ice entering the sea. As the ice slides over the glacier bed, frictional heat generates about 90% of the water at the base of the ice streams5. This water acts as a lubricant, speeding up the flow, which in turn generates more heat, and creates more water and slippage.
Glaciers in Greenland and at lower latitudes are relatively wet because their surfaces melt in summer, and rivers flow beneath them. In Antarctica, by contrast, there is little seasonal melting and much less water below the ice sheet. For example, the base of Pine Island Glacier releases about 50 cubic metres of water per second, which is only about 10 millimetres per year over the catchment area5. Removing this thin layer of water will slow the glacier, reducing frictional heating. The glacier will stall and its ice will thicken.