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 ice shelf.
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 on 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 global sea levels 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 global warming 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 sea level rise, 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.
"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.