Now there’s serious concern about Antarctica’s Thwaites and Pine Island glaciers. Satellite photos show that these vast ice sheets have been shrinking at a rate of about 1 kilometer a year. If they go away completely, the resulting floods could swamp low lying regions across the globe, with the Pacific and Atlantic coasts of the U.S likely to bear the brunt of the flooding.

Building underwater walls

Having dismissed atmospheric seeding and the pumping of sea water onto glaciers, many glaciologists now believe the best way to save glaciers may be to tackle the problem at the source. They suggest constructing enormous walls to prevent warm ocean water from eroding the glaciers’ ocean-facing edges, which jut out over and float upon the waves.

“In the polar oceans, you have warm salty water at depth with colder fresher water on top,” Wolovick says. “This warm water is the biggest threat as it causes the base of the floating ice to melt, and the glacier to become unstable. If you could block this water flow, it would reduce the melt rate.”

Made mostly of robot-excavated ocean sediment, the walls would extend from the ocean floor to the base of glaciers’ floating ice — holding it in place while shielding it from warm water.

The size of the wall would depend on the glacier in question. For a small one like the Jakobshavn glacier in western Greenland, Wolovick says, a 100-meter-high wall extending for about 5 kilometers might suffice. The much larger Thwaites glacier might require a 300-meter-high wall extending for 50 or more kilometers.

Would such walls really stop the ice from melting? Computer simulations suggest they would. A wall protecting Thwaites glacier, for example, might enable it to last another 400 centuries. That would buy us time, allowing people living along vulnerable coastlines to relocate or to build better sea walls — and perhaps we could use the time to find ways to ease global warming.

Cooling hot bedrock

Glaciers lose ice not just at the water’s edge but from underneath. That’s because glaciers are always moving toward the sea over a thin layer of water just above the underlying bedrock. As glaciers move along, their bottom surfaces scrape against the bedrock, generating friction and heat and causing some ice to melt. The problem is that with warming air temperatures causing additional melting, the volume of subglacial water is becoming larger, and glaciers are being accelerated toward the sea faster than they are being replenished.

Wolovick thinks it might be possible to tinker with the process and ameliorate much of the frictional heating by drilling a series of tunnels in the bedrock and pumping cold brine through them.

For the Pine Island glacier, he envisions a series of 5-meter-wide tunnels starting from the nearby Hudson mountain range and extending roughly horizontally in the bedrock for 80 kilometers or so. Once the brine starts flowing, he hopes it could freeze some of the water underneath the glacier, slowing the moving ice in its tracks, and giving the glacier time to strengthen and solidify.

A big debate

Wolovick is convinced that glacier geoengineering is our best bet for protecting the planet’s ice, and he’s not the only scientist who does.

“This is happening and we can’t really close our eyes and forget about the fact that we’re driving a dangerous mountain road,” says Slawek Tulacyzk, a professor of earth science at the University of California, Santa Cruz. “We’re either going to be defending the coastline in our own backyard, or we can try and decrease the risk at the source of the problem, where the ice is being discharged to the ocean.”

Other scientists disagree, saying that the money needed for the geoengineering schemes would be better spent on finding ways to lower the amount of the greenhouse gas carbon dioxide that is being pumped into the atmosphere.

“These approaches are not going to be effective at winning the war because the root cause of these changes is warming ocean and air temperatures, and addressing those is what’s needed for any lasting long-term framework,” says Twila Moon, a research scientist at the National Snow and Ice Data Center in Boulder, Colorado.

The debate over glacier geoengineering isn’t likely to go away anytime soon. But researchers from China are planning a $3 billion polar research study to evaluate the feasibility of the new proposals over the next decade. So maybe some cold, hard facts will help settle the debate.

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