Targeted engineering projects to hold off glacier melting could slow down the collapse of ice sheets and limit sea-level rise, according to a new study published in the European Geosciences Union journal The Cryosphere.

While an intervention similar in size to existing large civil engineering
projects could only have a 30% chance of success, a larger project would have
better odds of holding off ice-sheet collapse. But study authors Michael
Wolovick and John Moore caution that reducing
emissions still remains key to stopping climate change and its dramatic effects.

“Doing geoengineering means often considering the unthinkable,” says Moore, a
scientist at Beijing Normal University, China, and a professor of climate change
at the University of Lapland, Finland. The term ‘geoengineering’ is usually
applied to large-scale interventions to combat climate change. But instead of
trying to change the entire climate, Wolovick and Moore say we could apply a
more targeted approach to limit one of the most drastic consequences of climate
change: sea-level rise.

Their “unthinkable” idea is glacial
geoengineering: making changes to the geometry of the seafloor near glaciers
that flow into the ocean, forming an ice shelf, to prevent them from melting
further. Some glaciers, such as the Britain- or Florida-sized Thwaites ice
stream in West Antarctica, are retreating fast. “Thwaites could easily trigger a
runaway [West Antarctic] ice sheet collapse that would ultimately raise global
sea level by about 3 metres,” explains Wolovick, a researcher at Princeton
University’s Department of Geosciences, US. This could have dramatic effects to
the millions of people living in the world’s coastal areas.

Instead
of, or in addition to, limiting the effects of rising seas through traditional
coastal protection, using glacier geoengineering to stop the flood at the source
could be a viable option, as Wolovick and Moore show. “The most important result
[of our study] is that a meaningful ice sheet intervention is broadly within the
order of magnitude of plausible human achievements,” says Wolovick.

The team looked into two glacial-geoengineering designs. One idea would be to
build a wall underwater to block warm water reaching an ice shelf’s base, which
is very sensitive to melting. A simpler design consists of constructing
artificial mounds or columns on the seafloor: they wouldn’t block warm water but
could support and hold back the glacier, helping it regrow. “In either case, we
were imagining very simple structures, simply piles of sand or gravel on the
ocean floor,” says Wolovick.

The team ran computer models where they
applied these designs to Thwaites Glacier in a warming world. Thwaites is
projected to be the largest individual source of future sea-level rise and, at
80 to 100 km wide, it’s one of the widest glaciers in the world. “If [glacial
geoengineering] works there then we would expect it to work on less challenging
glaciers as well,” the authors write in The Cryosphere study
.

 

Brown represents bedrock, light blue represents grounded ice sheet, purple
represents floating ice shelf, and gray represents an artificial sill. Ocean
temperatures are drawn to represent the typical stratification faced by
marine-terminating ice streams: warm salty water at depth and cold fresh
water near the surface. Credit: Wolovick & Moore, The Cryosphere, 2018

The research shows that even the simpler design could slow down the rate
of sea-level rise, giving more time to coastal societies to adapt to rising
waters. The smallest intervention has a 30% probability of preventing a runaway
collapse of the West Antarctic Ice Sheet for the foreseeable future, according
to the models. This intervention would consist of building isolated
300-metre-high mounds or columns on the seafloor using between 0.1 and 1.5 cubic
kilometres of aggregate, depending on the strength of the material. This is
similar to the amount of material that was excavated to build the Suez Canal in
Egypt (1 cubic kilometre) or used in Dubai’s Palm Islands (0.3 cubic
kilometres).

A more sophisticated project, going beyond the scale
humanity has attempted so far, would have higher chances of success in avoiding
a runaway ice-sheet collapse within the next 1000 years (the time the
simulations run for), as well as better odds of causing the ice sheet to regain
mass. A small underwater wall blocking about 50% of warm water from reaching the
ice shelf base could have 70% chance of succeeding, while larger walls would be
even more likely to delay or even stop ice-sheet collapse.

When the bedrock slopes inward toward the continent, warm, deep ocean water
can flow downward under the ice shelf, chewing away at the grounding line.
Melting can be as much as 20 to 50 metres of ice thickness each year. As the
glacier’s base recedes, the brakes holding the continental ice ease up and
the glaciers feeding the ice shelf accelerate, and thus further thin and
recede the ice sheet. Credit: Jeremy Harbeck/NASA IceBridge

Despite the encouraging results, the scientists say they don’t advocate
starting these ambitious projects any time soon. While the simplest design would
be similar in scale to existing engineering projects, it would be built in one
of Earth’s harshest environments. So, the engineering details still need to be
worked out. Nonetheless, the team wanted to see whether glacial geoengineering
could work in theory, and wanted to get the scientific community to think about,
and improve on, the designs.

“We all understand that we have an
urgent professional obligation to determine how much sea level rise society
should expect, and how fast that sea level rise is likely to come. However, we
would argue that there is also an obligation to try to come up with ways that
society could protect itself against a rapid ice-sheet collapse,” says Wolovick.

Ice physics shows glacial geoengineering could work to hold off ice-sheet
collapse, but both Wolovick and Moore are adamant that reducing greenhouse-gas
emissions remains a priority in the fight against climate change. “There are
dishonest elements of society that will try to use our research to argue against
the necessity of emissions’ reductions. Our research does not in any way support
that interpretation,” they say.

Engineering glaciers would only
limit sea-level rise, while reducing emissions could also limit other harmful
consequences of climate change, such as ocean acidification, floods, droughts
and heat waves. In addition, the team points out that more warming would mean
glacial engineering projects would become less feasible and would have lower
chances of success. After all, their underwater structures might protect the
bottom of the ice shelves, but wouldn’t prevent warm air from eating away the
ice at the top.

“The more carbon we emit, the less likely it becomes
that the ice sheets will survive in the long term at anything close to their
present volume,” Wolovick concludes.

More information:

Wolovick, M. J. and Moore, J. C.: Stopping
the flood: could we use targeted geoengineering to mitigate sea level rise?,
The Cryosphere, 12, 2955–2967, 2018.

For further information, welcome to listen the open lecture of John C. Moore “Stopping the flood – Can
we engineer ice sheets and save the homes of a billion people?” on 24
October at 4 PM. The lecture takes place in Arktikum house in Rovaniemi, Finland
(Pohjoisranta 4). 

Research Professor John C. Moore
Arctic Centre, University of Lapland
+356 40 019 4850,
john.moore.bnu(at)gmail.com

Photo credit: Credit: NASA/Jim Yungel
Press release: The European Geosciences Union (EGU)