Glacial Geoengineering: The Key to Slowing Sea Level Rise?

The rapid collapse of some of the world’s biggest glaciers due to climate change will have devastating consequences for our planet’s coastlines due to sea level rise. Compounding this issue is the fact that many of these coastlines are heavily populated and developed. A recent proposal, first reported in The Atlantic, aims to avert potential catastrophe by turning to geoengineering through the construction of massive underwater walls, called sills, which would be built where glaciers meet the ocean in Antarctica and Greenland.

The idea is the work of Michael Wolovick, a glaciology postdoctoral researcher at Princeton University. The uniqueness of his geoengineering proposal is its focus on a consequence of climate change, in this case sea-level rise, as a result of glacial collapse, rather than a focus on decreasing greenhouse gases (GHG), the root cause of climate change. Many geoengineering proposals attempt to slow down or even reverse the Earth’s rising temperatures as an alternative to GHG mitigation through the addition of aerosols like sulfur dioxide to the atmosphere or increase in the reflectivity of clouds, while others explore ways to capture and subsequently sequester carbon.

Photo of the Jakobshavn glacier in Greenalnd.
The calving front of the Jakobshavn glaicer in western Greenland. The Jakobshavn is a potential site for the proposal’s walls (Source: NASA Goddard Space Flight Center/Creative Commons).

When asked about the inspiration behind his distinct work, Wolovick told GlacierHub he has been fascinated by the large scale societal implications that glacial collapse could have, given the relatively small scales of the glaciers themselves. The so called “doomsday glacier,” the Thwaites of West Antarctica, is only around 100 km wide, for example, but its collapse would swiftly destabilize large parts of the West Antarctic ice sheet, potentially leading to sea level rise of up to 13 feet in some parts of the world.

So how does Wolovick’s plan work? It starts with an engineering project of unprecedented scale, the construction of large underwater walls, composed of an inner layer like sand and an outer layer of boulders. These walls would be strategically built at the grounding line, where a glacier’s leading edge meets the ocean, of the world’s most unstable glaciers. These walls would be built primarily in Antarctica and Greenland where many glaciers extend beyond the land to float on the ocean.

Figuredetailing how ocean ending glaciers are melted from below
Figure detailing how ocean-ending glaciers are melted from below. The walls from this proposal would be placed in front of the grounding line pictured here (Source: Smith et al.).

Glaciers that extend from land into the ocean are exposed to both warming air and water temperatures. Warmer sea water melts these glaciers from below in addition to the melting that occurs from the air above, causing them to melt faster than glaciers solely confined to land. This is where the walls built on the ocean-floor would come into play. Once in place, the purpose of these barriers would be “to block warm water so you could reduce the melting rate, and also to provide pinning points that the ice shelf could reground on as it thickens,” according to Wolovick. In addition, because the glaciers are already floating, the walls would prevent warm water from moving further inland and increasing melting rates there.

Would these walls work in actuality? Wolovick’s computer modelling is in its early stages, but some models show glaciers stabilizing after walls are put in place, with some glaciers actually gaining in mass. This possible stabilization would buy some time to act decisively on adaptation to sea level rise and perhaps allow the prevention of disastrous ice sheet collapse altogether. Still, Wolovick admits a lot more work needs to be done in the future including the development of better ocean models to see if the walls would block warmer water in the way intended, allowing a glacier to stabilize.

Photo of a calving front of a glacier in West Antarctica
The calving front of a glacier in West Antarctica (Source: NASA Goddard Space Flight Center/Creative Commons).

While the proposal has the potential to slow glacial melting, Lukas Arenson, principal geotechnical engineer at BGC Engineering Inc. who spoke with GlacierHub about the proposal, says it is still in its very early stages, and there are many questions that need to be answered before implementation. One of Arenson’s principle concerns is “the enormous costs for building such a sill or a dike in a stable manner in these areas as it requires some major engineering and construction efforts.” Wolovick recognizes that his proposal would require placing a massive amount of material in front of glaciers, especially for wide ones such as the Thwaites.

There are also a plethora of engineering matters that need to be addressed. First, the foundations for the walls would need to be well protected. This protection could take the form of boulders and concrete elements or additional sills built in front of or at an angle to the main sill to redirect currents that could compromise its effectiveness, according to Arenson. Secondly, the seafloor on which the walls would be built could be “quite unstable and soft at places so that placing additional fill for a sill may be extremely challenging, potentially causing some local instabilities,” Arenson added. Finally, Wolovick states that it may be necessary to build the wall “underneath floating ice shelves, or in the vicinity of dense iceberg melange.” These efforts would further complicate what would already be a mega-engineering project.

Photo of an iceberg in Pine Island Bay
An iceberg floats in West Antarctica’s Pine Island Bay where the Thwaites glacier ends Source: NASA Goddard Space Flight Center/Creative Commons).

In addition to the technical aspects of the proposal, there are other issues to consider. There is also the question of where the material for the walls would come from and whether the walls might have detrimental impacts on sensitive Antarctic sea floor environments.

However, despite the many challenges ahead, the time is right to take action. As climate change progresses and glaciers around the world continue to melt, global sea levels creep up. One recent study projects an increase of 80 to 150 cm (close to five feet) by 2100, which would flood land currently inhabited by 153 million people. This geoengineering proposal will by no means solve every problem associated with climate change, like unabated human emissions of greenhouse gases, but with millions living along the coasts, it could provide humanity with something always in short supply, time.

Life on the Edge: The Science of Glaciers that Meet Oceans

Tidewater glacier on Antarctic coast (source: Jason Auch/Flickr)
Tidewater glacier on Antarctic coast (source: Jason Auch/Flickr)

In an October 2015 article in Earth & Space Science News, David Holland and Denise Holland suggest steps to increase the understanding of glacier melt to improve projections of sea level rise.

IPCC (Intergovernmental Panel on Climate Change) reports have concluded that anthropogenic causes are to blame for glacier retreat in the last century. They predict that increased melt in the present century will rise global sea levels. The authors report that the contribution of the West Antarctic Ice Sheet, alone will change low-lying coastal and communities worldwide and threaten marine ecosystems.

They note that the rate of sea level rise will be influenced by a number of factors, including the local shifts in the gravitational pull of land masses, along with changes in water currents, wind patterns, and water temperature and salinity. The rebound of land masses, once the weight of glaciers and ice sheets is removed, will also influence sea levels.

Map_of_the_McMurdo-South_Pole_highway
Map of Antarctica (source: Maximilian Dörrbecker [Chumwa])
The complex nature of the interface between ice sheets and the ocean also creates uncertainty about the future of many of the West Antarctic glaciers, as it is difficult to make predictions of how the ice will react in the future. In one possible scenario, the circulation of warm ocean waters that is currently held off by continued cold meltwater runoff from Antarctica could grow larger, and the cold water barrier would no longer block it from teaching the continent. The warm water would thus be able to make direct contact with the underside of the glacier and warm it from below, greatly increasing the glacier melt.

Holland and Holland note that many problems with predicting the effects of West Antarctic glacier melt stem from a deficit of data. Though satellites are able to measure glacier volume, they are unable to observe the water resting underneath glaciers or the land mass upon which some glaciers rest. Another area of difficulty in predicting the melting of the West Antarctic glacier involves a shortfall in scientific understanding of calving—the process in which the section of a glacier front breaks and falls into the ocean. Scientists compare the difficulties of constructing models of calving to the challenges of predicting earthquakes. They remain unable to make long-term predictions about when they will occur.

https://upload.wikimedia.org/wikipedia/commons/b/b2/Antarctic_shelf_ice_hg.png
Sketch of the Antarctic coast showing interactions of ice sheet, glaciers and oceans. (Source: Hannes Grobe, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany )

Holland and Holland state that in order to create accurate predictions for the contributions of the West Antarctic Ice Sheet to sea level rise, scientists need to couple glacier and ocean models. Currently there is little cooperation between glaciologists and oceanographers, even though both work on sea level rise since each uses separate models specific to their disciplines. To address this problem Holland and Holland report, the World Climate Research Programme (WCRP) has established a project, Climate and Cryosphere (CliC). This project held a meeting in October 2014, in which the Marine Ice Sheet–Ocean Model Intercomparison Project (MISOMIP) was established. The project seeks to draw on the efforts glaciological and oceanographic modelers. The participants in the project work together to create coupled and interactive glacier-ocean models. The goal is to follow this suite of glacier-ocean models with regional simulations of specific outlet glaciers such as those found in West Antarctica.

Holland and Holland say that scientists, by coupling glacier and ocean models, can greatly improve the accuracy of future sea level rise projections attributed to the West Antarctic Ice Sheet and its outlet glaciers. Because of the increasing threat of sea level rise to communities around the world, the accuracy of such projections is of great value. It is to be hoped that this importance will support efforts to produce these projections, which require increased cooperative effort between nations and between disciplines.