For years, scientists have been exploring ways to save the vast sheets of ice covering Greenland and Antarctica, which as the climate warms are melting and falling into the ocean.
They've proposed all sorts of possible fixes, from seeding the atmosphere with sunlight-blocking chemicals to cool the planet to pumping seawater onto the ice with the hope that it will freeze and replenish lost ice. But these ideas have been widely criticized for their exorbitant cost — thought to be in the hundreds of billions of dollars a year — and the risks involved.
Now scientists have come up with bold new plans for protecting these massive glaciers — and preventing the potentially devastating rise in sea levels that would occur if they vanished. One involves protecting vulnerable glaciers with underwater walls built by robots; the other proposes pumping cold water through vast tunnels bored under the ice to thicken it and keep it from sliding into the ocean.
"These geoengineering projects could delay much of the polar glaciers from melting into the sea for centuries," says Michael Wolovick, a glaciologist at Princeton University and one of the scientists behind the new proposals. "Other ideas have been proposed, but the energy costs have been vast. Pumping water on top of polar glaciers also runs the risk of the water draining to the bed of the glacier, lubricating it further, and increasing the rate at which it is sliding into the sea."
Implementation of the plans would likely cost tens of billions of dollars. While this is a fraction of the price tag of the other initiatives suggested, wide international cooperation would be needed not just to fund the projects but to manage them.
Why glaciers matter
Underwater walls and subglacial tunnels sound drastic, but their proponents say they may be the best way to prevent significant sea level rise as the planet continues to warm. If we do nothing, the oceans are projected to rise more than a meter by 2100. That would pose a grave danger to the 150 million people across the globe living in coastal areas — and could give the global economy a $50-trillion-per-year hit.
Scientists are especially worried about sudden glacial loss. That happened in 2002, when a chunk of ice the size of Rhode Island broke off the east coast of the Antarctic Peninsula and crashed into the Larsen Sea.
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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