If the world is going to experience catastrophic sea-level rise—the kind of worst-case scenario spun out of climate models that would force humanity to flee from the world's coasts—there's a good chance it could all start with the collapse of Thwaites Glacier.
If Thwaites goes, it could trigger a chain of events that destabilizes the West Antarctic ice sheet, with a recent Rolling Stone feature dubbing it the "doomsday glacier." The bad news is that Thwaites isn't particularly stable itself. It is the poster child of what scientist Hans Weertman named "marine ice sheet instability" in the 1970s. The glacier's grounding line—the place where it is attached to the Earth's bedrock—lies below sea level, making it vulnerable not just to melting from warming air, but, more importantly, from below. Warm ocean water is slowly causing Thwaites' grounding line to retreat. In 2014, two studies concluded this process is already occurring.
With the world still nowhere near the emissions reductions needed to stave off significant global warming, Princeton University glaciologist Michael Wolovick thinks it's not a bad idea to consider other ways to forestall marine ice sheet collapse. This week, he is presenting as-yet unpublished research that looks at the possibility of building an artificial sill in the ocean to support Thwaites or other glaciers with similar structures. It would basically be a crutch—perhaps a mass of material protected by boulders rising from the sea floor—that serves to block warm water.
"It could slow the marine ice sheet collapse or, in some cases, reverse it," he told Oceans Deeply, based on what his, admittedly very preliminary, simplified modeling has shown.
Even if it could work, building a sill large enough to stabilize Thwaites would be an unprecedented and astronomically expensive ocean infrastructure project that falls somewhere between adapting to climate risks and geoengineering the Earth to forestall them. Serious discussion of such ideas has long been controversial. Geoengineering of any kind risks offering intransigent politicians excuses to keep spewing carbon and inevitably leads to negative or unintended consequences and ethical quandaries. Still, today scientific discussion of even more radical ideas that directly reduce the planet's temperature—from seeding the atmosphere with cooling sulfate aerosols, to fertilizing the ocean with iron, to marine cloud brightening to reflect sunlight—is now growing louder and more serious.
"We've dallied so long with respect to reducing carbon emissions ... that we are confronting the fact that we need to think outside of the box about how to stave off the worst impacts of climate change," said Peter Frumhoff, chief climate scientist for the non-profit group Union of Concerned Scientists. Although emissions reductions clearly need to come first, he said, increasing climate risks are leading to the serious discussion of creative ideas—even ones that have seemed like terrible last-ditch options, such as spraying aerosols into the upper atmosphere.
As polar regions experience the effects of climate change at the fastest rate, several of these newer proposals specifically seek to save polar ice—both land-based ice sheets, as in Wolovick's proposal, and sea ice—and were presented among a number of proposals at two geoengineering sessions of last week's meeting of the American Geophysical Union, one of the largest gatherings of earth scientists.
Melting sea ice, unlike ice sheets and glaciers, doesn't contribute to sea-level rise, but the loss of the reflective ice surface in the ocean accelerates warming rates globally and has already seriously threatened Arctic ecosystems and cultures. Experts believe the Arctic could be ice-free in the summer as early as 2030.
This is why one proposal, from the Ice911 Research Corporation, led by Stanford University lecturer Leslie Field, imagines spreading a reflective material on polar ice to reduce its melting rate. Another, first published in a journal earlier this year, looks at actually building thicker sea ice.
Scientists at Arizona State University calculated that wind-powered pumps could spray ocean water on top of Arctic sea ice in the winter. The idea is that the water would freeze and create up to three feet of new sea ice a year, in theory reversing current momentum toward an ice-free Arctic if carried out over 10 percent of the Arctic. At a smaller scale, the same approach could save sea ice in key regions that are, for instance, critical polar bear habitat.
"This has potentially fewer negative consequences than, say, a sulfate aerosol method of cooling the planet, and it's reversible. If you don't like the outcome of making thicker ice, you could stop," said Arizona State University scientist Hilairy Ellen Hartnett, who co-authored a paper with lead author Steve Desch and other colleagues. She said her team is currently looking for funding to move from modeling to lab-scale testing of the idea.
"We need more ideas about geoengineering," she said. "The conversation is really focused on carbon dioxide removal and sulfate aerosols, and there really aren't that many other options that people talk about."
Like Hartnett, Wolovick believes that, in theory, his artificial sill idea might be especially feasible because it targets a limited geographic area while potentially having a much larger global benefit. In Greenland, important outlet glaciers are about three miles wide—humans have built bridges that are much longer, he noted. While no underwater structure has been built quite as big as the one that could be needed to stabilize Thwaites Glacier, he said, many have been constructed on land and he believes the engineering could be relatively straightforward.
"Compared to the amount of global societal impact that would happen if Thwaites were to have a runaway collapse, [the cost] might not be so big in comparison," Wolovick said. So far, however, he has done only relatively simple modeling to show how it might work.
The scientists behind these proposals all emphasize that such ideas can't replace greenhouse gas emissions reductions and would really only be stopgap measures. And even if such climate interventions prove to be feasible, they would cost inordinate sums and likely have downsides at local, regional, or global scales.
So far, Peter Frumhoff said, the world has lacked a formal governance structure to hash out all kinds of climate intervention approaches. He believes this is needed before ideas—especially those that aim to directly change the Earth's temperature—move from computer models to field tests. "These serious scientific conversation need to be coupled with serious, meaningful public dialogues," he said.