The seas are rising—currently at a rate of 3.3 millimeters per year, for a total of perhaps 240 millimeters since the industrial era began. Around a third of the rise so far has been due to the ocean expanding as it warms; the rest owes to ice on land melting. The Greenland and Antarctic ice sheets are two huge reservoirs of this land-based ice: if both entirely melted, they could contribute 7 meters or 60 meters of sea-level rise respectively—more than enough to utterly reshape the continents humans have called home for so long.

Things tend to move at a glacial pace in the frozen ice caps of cryosphere, at least by human standards. Even under the most extreme climate change scenarios, these ice sheets are not expected to melt for centuries to come, and are unlikely to contribute more than one meter to sea-level rise at the end of this century.

However, even this sea-level rise could be sufficient to cause trillions of dollars a year worth of damage, or require billions of dollars of flood-defense infrastructure to be built to protect low-lying cities.

Of particular concern is the West Antarctic Ice Sheet, which is vulnerable to the marine ice-sheet instability. Essentially, warm waters slosh around the base of glaciers and the ice-sheet, melting it and undermining it from below, causing it to retreat over the next few centuries. Thwaites, a glacier the size of Florida, may already be doomed to melt over the next few centuries, and could even prove to be the gateway that allows for a more widespread collapse of the West Antarctic Ice Sheet.

Glacial Geoengineering?

Faced with this grim, slow-moving catastrophe, some scientists are questioning whether we might consider radical action to save the Antarctic glaciers: a kind of targeted geoengineering that might slow down or even prevent this ice sheet from melting, buying time for humanity to adapt its coastal settlements to a world with a few meters of sea level rise.

One way you might seek to do this is fairly intuitive: build a wall, a large underwater barrier that prevents warm water from melting and undermining the base of the glacier. In simulations conducted by Dr Mike Wolovick and Professor John Moore, building such a barrier was able to preserve the Thwaites glacier even after the marine ice sheet instability had been triggered and the glacier had begun to collapse. Even smaller interventions, such as providing a sill or a few isolated “pinning points” of rock for the glacier to reground itself on, had a 30 percent chance of saving the glacier once the marine ice sheet instability had already begun.

Of course, it’s comparatively easy to simulate what might happen if you built a gigantic wall across the mouth of a glacier; the actual engineering project is a much more difficult undertaking. Antarctica is not an ideal environment for large-scale building projects, although research stations on the desert continent are increasingly impressive. Blocking water flow to the Thwaites glacier could require a wall 120km long, with a depth of 600 meters: by comparison, the One World Trade Center building is 540m tall, and Hadrian’s Wall between Scotland and England is around 120km long. If such a glacier stabilization project were ever pursued, it would easily be the largest engineering project humans have ever conducted.

And there is no guarantee that even such a huge scheme would work. Simulations by the same researchers have found that diverting the warm water from one glacier, if done incorrectly, can accelerate melt in neighboring regions. As ever with climate-related research, more detailed modeling—and better models, driven by better observations and physical understanding—are necessary before we can be confident of how something unprecedented like this might work.

Desperate Times, Desperate Measures

The researchers suggest that, if we decide glacial geoengineering is worth actually pursuing, it would be advisable to start on a smaller glacier. There are several candidates in Greenland, such as the Jakobshavn glacier. The slow pace of the marine ice sheet instability gives us some advantages here: the project could take decades or even centuries, and still avert some damaging sea level rise. We would be able to observe the glacier to see if any adverse consequences took place, and improve the design of our interventions to make them more cost-effective over time.

Aside from unintended consequences, one of the main concerns that arise from the contemplation of any geoengineering project is the fear of a moral hazard. In other words, if humans decide that we can simply engineer our way out of the problems we’ve created by wanton environmental destruction and rampant industrialization, we might not focus—as we must—on cutting carbon emissions and living in a more sustainable way.

Every year that goes by, as our emissions staggeringly continue to rise, we are relying on grander technological miracles to bail us out, such as capturing billions of tonnes of carbon dioxide and burying it underground by the end of the century. It is a truly terrifying proposition that, rather than kick the fossil fuel habit and live within planetary boundaries, we might instead try to reflect sunlight or prop up glaciers, kicking the climate in ways we’ve never seen before. It’s the equivalent of trying to sober up with a quadruple espresso, when you should never be drunk behind the wheel in the first place.

Yet, as we continue to pour greenhouse gases into the atmosphere, these ideas deserve researching to see if any of them can alleviate suffering—in the hope, if not the expectation, that we will never have to take such awful risks.

But in the specific case of the Antarctic glaciers, it may already be too late: if the marine ice sheet instability has been triggered, they will collapse, even if it takes centuries. Reducing carbon emissions, or even cooling the planet, likely cannot prevent this from happening—although there are countless other excellent reasons to cut our emissions to zero —and our grandchildren and their grandchildren will have to live with the consequences. In this circumstance, last-ditch measures may be all we have.

Image Credit: Alto Crew / Unsplash

Thomas Hornigold is a physics student at the University of Oxford. When he's not geeking out about the Universe, he hosts a podcast, Physical Attraction, which explains physics - one chat-up line at a time.

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