The greatest uncertainty in forecasting global sea level rise is how Antarctica’s ice loss will accelerate as the climate warms. Two studies published Aug. 10 and led by researchers at NASA’s Jet Propulsion Laboratory in Southern California reveal unexpected new data about how the Antarctic Ice Sheet has been losing mass in recent decades.
One study, published in the journal Nature, maps how iceberg calving – the breaking off of ice from a glacier front – has changed the Antarctic coastline over the last 25 years. The researchers found that the edge of the ice sheet has been shedding icebergs faster than the ice can be replaced. This surprise finding doubles previous estimates of ice loss from Antarctic’s floating ice shelves since 1997, from 6 trillion to 12 trillion metric tons. Ice loss from calving has weakened the ice shelves and allowed Antarctic glaciers to flow more rapidly to the ocean, accelerating the rate of global sea level rise.
The other study, published in Earth System Science Data, shows in unprecedented detail how the thinning of Antarctic ice as ocean water melts it has spread from the continent’s outward edges into its interior, almost doubling in the western parts of the ice sheet over the past decade. Combined, the complementary reports give the most complete view yet of how the frozen continent is changing.
“Antarctica is crumbling at its edges,” says JPL scientist Chad Greene, lead author of the calving study. “And when ice shelves dwindle and weaken, the continent’s massive glaciers tend to speed up and increase the rate of global sea level rise.”
Most Antarctic glaciers flow to the ocean, where they end in floating ice shelves up to 2 miles (3 kilometers) thick and 500 miles (800 kilometers) across. Ice shelves act like buttresses to glaciers, keeping the ice from simply sliding into the ocean. When ice shelves are stable, they have a natural cycle of calving and replenishment that keeps their size fairly constant over the long term.
But in recent decades, the warming ocean has been destabilizing Antarctica’s ice shelves by melting them from below, making them thinner and weaker. Satellite altimeters measure the thinning process by recording the changing height of the ice, but until this study, there hasn’t been a comprehensive assessment of how climate change might be affecting calving around the continent.