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)