The Thwaites Glacier in western Antarctica (
Fig. 1) keeps glaciologists and climate scientists awake at night. The 120 km-wide glacier loses about 45 billion tonnes of ice each year, accounting for about 4% of global sea level rise
[1]. If it melted completely, sea levels would climb 65 cm, and follow-on effects could lead to a 3 m increase
[2].
But if some scientists’ vision becomes reality, in 10–15 years construction crews will sail into the Amundsen Sea off Antarctica to begin building an 80 km long underwater curtain that will shield the glacier from the warm currents that are accelerating its decline
[3]. That project, which might cost 80 billion USD
[3], is just one of the audacious proposals for geoengineering the world’s dwindling glaciers to limit sea level rise
[4]. Other approaches that scientists have suggested include drilling deep into glaciers to drain the water that speeds their slide into the ocean, spraying water onto thinning glaciers to rebuild them, and constructing giant fences to promote snow buildup atop glaciers
[4],
[5].
Uncertainties about glacier geoengineering abound. Whether any of these approaches is technically feasible is unknown. The costs of such projects—and who would pay them—are unclear. The environmental side effects remain undefined. And whether people who would be affected by the projects will agree to them is a mystery [
4,
6].
A panel of eminent glaciologists says it is time to start answering these questions. Their July 2024 report does not endorse glacier geoengineering but argues for a concerted research program into whether it is possible, which would include a doubling of the funding for investigating glaciers
[7]. “Even if there is only a 10% chance that this is feasible, it is worth finding out,” said John Moore, research professor at the University of Lapland in Rovaniemi, Finland, and one of the report’s co-authors. Moore and his colleagues are trying to raise 10 million USD to perform the first pilot study of glacier geoengineering, which would involve stretching a curtain up to 1 km long across a fjord.
However, some researchers oppose glacier geoengineering and argue that even studying the possibility could drain funds from other vital research and discourage more realistic actions to reduce carbon emissions. “We need to put our money and efforts into shifting away from fossil fuels,” said Leigh Stearns, professor of earth and environmental sciences at the University of Pennsylvania in Philadelphia, PA, USA.
The world’s glaciers are receding because of climate change. Since the 1970s, the average thickness of 61 “reference” glaciers that scientists have been monitoring has declined by about 30 m
[8]. Average sea level has risen about 20 cm since 1900 and, according to recent estimates, could climb an additional 20 cm to 2 m by 2100
[9].
Glaciers melting in two parts of the world, Greenland and Antarctica, which between them harbor 99% of the world’s freshwater ice
[10], could have the biggest impact on sea level. One reason that the Thwaites Glacier is vulnerable is because it sits on land that is below sea level, and sea water is pouring beneath the glacier and eroding it from below
[11]. In addition, a floating layer of ice known as an ice shelf keeps part of the glacier from flowing into the ocean. However, a current of warm water is undermining this shelf, which could accelerate the glacier’s collapse into the sea
[11],
[12]. The latest results from a team of scientists studying the glacier suggest that it may not collapse until 2300, but its gradual shrinkage could still increase sea level by 6 cm over this century
[2].
What is true of the Thwaites Glacier is also true of other large glaciers. “We do not know enough about these glaciers to say that they have crossed the line” and will inevitably collapse, said Douglas MacAyeal, professor of geophysical sciences at the University of Chicago in Chicago, IL, USA, and another co-author on the report. “But we may be in a position to avoid catastrophic sea level changes.”
The idea of taking action to preserve glaciers and curtail sea level rise dates to the 1980s
[7]. In 2018, Moore and three colleagues spelled out several potential strategies
[13]. The Jakobshavn Glacier in Greenland (
Fig. 2), for instance, is sliding into the sea, where it contacts relatively warm water
[13]. Melting of this glacier alone accounted for 4% of sea-level increase in the 20th century
[13]. Moore and colleagues proposed constructing a 100 m-tall, concrete-coated embankment on the sea floor in Disko Bay, the fjord where the glacier reaches the sea. The berm would divert warm water away from the glacier, theoretically slowing its deterioration
[13].
Moore said that when he and his co-authors made this proposal, “we were not engineers, we were very naive scientists.” Experts with experience in underwater construction pointed out that a flexible curtain would work better and be more durable than a wall, said Moore. He and his team have been collaborating with the energy engineering company Aker Solutions of Fornebu, Norway, to improve the design. If they can raise enough money, he said they plan to install a curtain of biodegradable fabric between 100 m and 1 km long. Instead of a solid layer, the material would be divided into strips and anchored to the bottom, an arrangement that would allow icebergs to cross the curtain without destroying it
[6]. Moore will not disclose the location of the planned test, but he hopes to begin it within 2–3 years.
Preliminary research like this is essential, and scientists will need to perform 5–10 such trials to determine whether interventions are practicable and worth attempting on large, vulnerable glaciers, said Ken Mankoff, senior scientific programmer at the US National Aeronautics and Space Administration’s Goddard Institute for Space Studies in New York City, NY, USA. “If these studies reveal that glacier engineering can work, it might be a good tool to have. It does not mean we have to use it,” said Mankoff, who is also a report co-author.
Still, some researchers are already certain that glacier geoengineering should not be attempted. “The solutions being proposed do not make sense in terms of the problems we are seeing,” said Stearns. For example, the projects may not actually slow ice loss. Diverting warm water from the Thwaites Glacier might just speed the melting of ice elsewhere
[14]. Redirecting ocean currents could disrupt nutrient circulation, damage fisheries, or cause other detrimental environmental effects
[6],
[15]. Stearns said that if some of the proposed approaches get the go-ahead, it will take decades to determine whether they are saving glacier ice. And if they are not working, it might be too late to try other measures.
Making glacier geoengineering a reality will require not only scientists and engineers, but also diplomats, policy makers, lawyers, and other experts. Two major issues that need to be resolved are funding and governance (who will control the projects and decide on their locations). Although cost estimates are uncertain, extensive glacier geoengineering would likely require tens or hundreds of billions of dollars, said Moore. So far, he and his colleagues have obtained the money for their research from philanthropists, but governments would likely have to step in as projects grew larger, he said.
The costs will be substantial, Moore added, but they are relatively small compared with the trillions of dollars that will be required for new infrastructure, such as sea walls, to protect low-lying areas of the globe. MacAyeal adds that the number of candidates for geoengineering is small, which will help keep costs down. Targeting just three Antarctic glaciers—the Thwaites Glacier, the neighboring Pine Island Glacier, and the Totten Glacier—could make a big difference for sea level rise, he said.
Governance is a particularly tricky issue for glacier geoengineering. Putting up underwater curtains off Greenland, for example, would likely require approval from the Inuit, the native inhabitants of the island
[6]. But it is not clear if they would sanction construction that could disrupt the fisheries they depend on
[6]. MacAyeal noted that similar projects in Antarctica would likely violate the Antarctic Treaty System, the set of international agreements that prevents activities that could harm the environment on the continent
[16],
[17]. To permit any glacier geoengineering projects, the 29 consultative parties to the treaty, which include the United States, Russia, and China, may have to agree to amend the provisions, said Moore. In the end, “governance is likely to be a lot slower than the science,” he said.
Even if glacier geoengineering works, it will not be a panacea for the problem of sea level rise, Mankoff cautioned. With the rapid rise in atmospheric CO2 levels in the last few decades, the strategy “is like putting on your seatbelt when you are driving drunk toward a cliff,” he said. “But it might buy us some time.”
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