Melting Ice Shelves Show Razor-Thin Risk Margins on Warmer Earth

(Bloomberg) -- Accelerating climate change is poised to unleash vast reservoirs of water into the world's oceans, potentially resulting in higher sea levels and severe economic damage to coastal populations. 

The new assessment shows the mounting risks posed by unstable ice shelves in Antarctica and suggests the margin for error is shrinking for the world's economies to address climate change. Research published this week in the journal Geophysical Research Letters concluded that 34% of ice shelves could collapse this century under current global warming trajectories. 

"These ice shelves act like dams and keep the ice on the continent," researcher Christoph Kittel said. “Without these platforms, huge amounts of ice would flow directly into the ocean, leading to a consequent rise in sea levels.”

Sea levels could rise by at least 20 centimeters (7 inches) if just a fraction of the ice shelves studied in the report failed, a scenario deemed likely if average global temperatures warmed by 4 degrees Celsius by the end of the century. Keeping temperatures within the 1.5 degree Celsius boundary of the Paris climate agreement would dramatically reduce the volume of lost ice shelves. 

The most recent example of a broken ice shelf happened in February, when a sheet of ice the size of Los Angeles broke into Antarctica's Weddell Sea. In 2002, the sudden collapse of the Larsen B ice shelf dumped 3,250 square kilometers of ice into the ocean over a matter of weeks. While the loss of ice shelves themselves don't contribute to rising seas because they already rest on water, their destruction clears a pathway for melting glaciers to run off into the ocean. 

“Ice shelves act as a barrier to glaciers, so when they disappear, it's like pulling the plug in a sink, allowing glaciers to flow freely into the ocean, where they contribute to sea level rise,” said Ella Gilbert, researcher and co-author. “As the climate warms, ice shelves are more likely to collapse and accelerate global sea level rise.”

The researchers said their findings underscore the need to limit temperature increases to 1.5 degree Celsius — a mark that the world's economies are currently on track to hit by March 2034. They also suggest that the Intergovernmental Panel on Climate Change may be underestimating the impact that lost ice shelves will have on sea-level rise.  

“The extent of ice shelf mass loss and the precise fate of individual ice shelves depends primarily on the amount of warming that occurs,” they said. “The implication is that warming of 4°C above pre-industrial levels will almost quadruple the area vulnerable.”

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