Propping up glaciers to avoid cataclysmic sea level rise

September 20, 2018 by Marlowe Hood
This NASA picture shows part of the Thwaites glacier, in Antarctica, which is the size of Britain

As global warming outpaces efforts to tame it, scientists have proposed building massive underwater structures to prevent an Antarctic glacier the size of Britain from sliding into the sea and lifting the world's oceans by several metres.

The more modest of two engineering schemes—which is still on the scale of a Panama or Suez Canal—to shore up Thwaites Glacier would require the construction of Eiffel Tower-sized columns resting on the seabed to support the glacier's ocean-facing edge, or .

Option Two is a 100-metre tall underwater wall, or berm, running 80-100 kilometres (55-60 miles) beneath the ice shelf to block bottom-flowing warm water that erodes the glacier's underbelly, rendering it unstable.

The ambitious projects, detailed Thursday in the European Geophysical Union journal The Cryosphere, reflect a gathering awareness that slashing planet-warming greenhouse gas emissions—while essential—may not happen quickly enough to avoid catastrophic climate change impacts.

"Thwaites could easily trigger a runaway ice sheet collapse that would ultimately raise by about three metres," said lead author Michael Wolovick, a researcher at Princeton University's Geophysical Fluid Dynamics Laboratory.

Nor will reducing carbon pollution be enough: any credible pathway to a world in which is capped below two degrees Celsius above pre-industrial levels (3.6 degree Celsius)—the target enshrined in the 2015 Paris climate treaty—depends on sucking large quantities of CO2 out of the air.

As a result, geoengineering schemes once dismissed as impractical, unnecessary or outright dangerous—injecting particles into space to deflect the sun, storing CO2 in the ground, planting millions of square kilometres in biofuels—have rapidly moved from the margins toward the centre of scientific and policy discussion.

But none of these schemes address , which is likely to cause more human misery than any other climate impact: by century's end, it could swamp dozens of island states and densely populated river deltas, especially in Asia and Africa.

Runaway collapse

"The scientific community should carefully investigate the possibility of glacial geoengineering," said Wolovick. "There are hundreds of millions of people who live within a few metres of sea level."

Until recently, sea level rise was caused mainly by ocean water expanding under the influence of global warming. Today, the biggest driver is run off from ice sheets sitting atop the island of Greenland and the continent of Antarctica.

Taken together, Greenland and West Antarctica—more vulnerable to global warming than East Antarctica—contain enough frozen water to lift the ocean watermark by about 12 metres.

For Thwaites, there is an added sense of urgency.

Presentation of a concept study assessing the viability of constructing massive submarine walls to slow the melting of glaciers and ice sheets and limit sea level rise.
"It may already have passed the tipping point, we won't know for sure for a decade or two," said co-author John Moore, chief scientist at the College of Global Change and Earth System Science at Beijing Normal University.

"But the acceleration starts slowly, so we will have a century or so to prevent runaway collapse."

Wolovick and Moore ran computer models to test their geoengineering schemes, taking into account the known variables influencing glacier-ocean dynamics.

The underwater towers—which could be built with material dredged from the continental shelf or quarried from exposed rock—stood a 30 percent change of significantly slowing the glacier's disintegration.

Initially sceptical

"We show that it is possible to stabilise glacier beds by providing extra pinning points they can use to support themselves," said Moore.

Building a berm to block the warm water eating at Thwaites' underside doubled the odds of success, but would likely carry a price tag in the hundreds of billions of dollars, they found.

"It is nowhere near ready for implementation, and the potential side effects require much more research", Wolovick said.

The goal of the study, he added, was mostly to spark a conversation among scientists.

"Initially, I was very Skeptical," said Moore. "But compared with the alternatives, the idea certainly deserves to be much better researched and investigated."

The researchers also emphasised that geoengineering solutions do not lessen the need for reducing humanity's output of greenhouse gases, which hit record levels in 2017.

"There are dishonest elements of society that will try to use our research to argue against the necessity of reducing emissions," said Wolovick. "Our research does not in any way support that interpretation."

"The more carbon we emit, the less likely it becomes that the ice sheets will survive in the long term."

Explore further: Glacial engineering could limit sea-level rise, if we get our emissions under control

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4 comments

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aksdad
1.7 / 5 (7) Sep 20, 2018
Sea level rise has been occurring for about 15,000 years since the end of the last glacial period as continent-sized glaciers covering much of Canada, northern Europe and Russia began melting.

https://en.wikipe...l_period

This has happened repeatedly over the last 800,000 years or so as ice core data shows.

https://www.clima...arge.png

At the peak of the prior interglacial warm period 125,000 years ago, sea levels were 4 to 6 meters higher than today (13 to 20 feet).

https://www.giss....nitz_09/

That suggests that there may be more sea level rise in the future, regardless of whether or not humans are contributing to global warming. Luckily the rate of rise is so small, around 3 mm per year globally (8 to 13 inches per hundred years), that the impact will be unnoticed over a normal lifetime, but urban planners should take it into consideration.

http://sealevel.colorado.edu/
TheGhostofOtto1923
4 / 5 (4) Sep 20, 2018
Ah. Massive taxpayer-funded megaprojects to delay the inevitable. Instead, why not incentivize the development of new communities inland to replace aging coastal cities which are already reaching the end of their habitability?

Civilizations have always been mobile. Cities wear out and entropy means it costs more to fix them than to build anew. New development generates revenue, jobs, profits. Starting from scratch means cities that are more rationally designed, more efficient, more in tune with the latest tech and environmental concerns.

Businesses have been abandoning these obsolete cities for a long time now, in part because it becomes more and more expensive to fix and modify them, and taxes have to be increased as a result. And as business leaves, workers follow, reducing the revenue base even further. A vicious and irreversible cycle.
Cusco
3.7 / 5 (6) Sep 21, 2018
This has happened repeatedly over the last 800,000 years or so


As I'm sure you've had pointed out to you before, all previous occurrences happened over the period of thousands of years, not decades. Temperatures have never changed this fast. We're in unknown territory here.
barakn
4 / 5 (4) Sep 21, 2018
That suggests that there may be more sea level rise in the future, regardless of whether or not humans are contributing to global warming. Luckily the rate of rise is so small, around 3 mm per year globally (8 to 13 inches per hundred years), that the impact will be unnoticed over a normal lifetime, but urban planners should take it into consideration.

Blindly assuming a constant rise should get an urban planner fired. You appear to be under the misguided notion that sea level is the same everywhere. Because of differences in density, currents, wind patterns, and gravitational tugs from landmasses, ice, and underwater topography, the sea is not flat and is ever changing. Combined with the change in height of land itself (tectonics, isostatic rebound), some areas may see no rise or even a decline in relative sea level, others may see a rise much larger than average. This is no time to apply a one size fits all approach to urban planning.

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