Antarctica is home to 90% of the world’s freshwater, trapped in the continent’s vast ice sheets — and the stability of much of that ice is seriously threatened by global warming. Two studies published in the journal Nature this week looks at how climate change is shaking conditions in Antarctic ice sheets, spelling from the grim potential future of sea level rise.
The first study looks how the two of Antarctica are ice caps are affected by what happens to their ice shelves, that serve as protective buttresses. ice shelves stretch over the oceanwhile the sheets cover the land.
“Ice shelves are huge, hundreds or even thousands of meters thick chunks of ice, and a few are the size of France,” said lead author Chad Greene, a postdoctoral researcher at NASA. Jet Propulsion Laboratory, in an email. “Ice shelves float on the ocean in hydrostatic equilibrium, so if an iceberg breaks off an ice shelf, it has no direct impact on sea level. But when an ice shelf calves, it gets a little smaller and a little weaker.”
Ice trays normally have a healthy calving cycle and are able to regenerate the lost ice. But climate change has accelerated the calving process, weakening the ice shelves from below in warm water and making it more difficult to replenish the shelves. To understand what this might mean for sea level rise, Greene and his fellow researchers used satellite data to generate a series of high-resolution maps of Antarctica’s coastline over the past 25 years.
“What we found is that Antarctica’s ice shelves are crumbling at the edges,” Greene says. In general they are determined that Antarctica has lost more than 14,280 square miles (37,000 square kilometers) of ice shelf area since 1997 (“That is about the size of Switzerland,” Greene added). That means that the continent’s ice shelves have lost about 12 million tons in the past 25 years, about double previous estimates of the loss. All this crumbling could spell bad news for the long-term stability of the continent’s ice sheets.
“Over the past quarter of a century, the shrinking and weakening of ice shelves has accelerated Antarctica’s massive glaciers and increased their contribution to sea-level rise,” Greene said. “The most significant effects have been seen at the Thwaites and Pine Island glaciers in West Antarctica, and there are no signs that either will slow down in the near term.” (The Thwaites Glacier is commonly referred to as the “Doomsday Glacier”, and it’s in pretty big problem.)
Even ice sheets that were once thought to be stable show signs of stress. One second study out this week looks at the potential fate of an incredibly important ice sheet – the East Antarctic Ice Sheet, the larger of the two continents ice caps and the largest freshwater reservoir on earth. This ice sheet is traditionally considered to be better protected than the weastern ice sheet — which includes the Thwaites and Pine Island glaciers — due to less exposure to warming ocean waters. But if the East Antarctic Ice Sheet is ever threatened, it will be potentially catastrophic news for the planet: The ice sheet will hold enough water to raise sea levels by more than 52 meters.
“We know that small mountain glaciers around the world are shrinking rapidly and contributing to sea level rise,” said Chris Stokes, lead author of the study and professor of geography at Durham University.said in a e-mail. “We also know that the much larger Greenland ice sheet is also losing mass and contributing to sea level rise, as is the western portion of the Antarctic ice sheet. However, we know much less about what could happen to the East Antarctic Ice Sheet.”
To get a better idea of what the future of the East Antarctic Ice Sheet might look like, Stokes and his co-authors reviewed previous work on how the ice sheet responded to past warm spells and current levels of change. , supplemented by “Cracking some new numbers based on computer simulations predicting how much this giant ice sheet could contribute to future sea level rise,” he said.
There’s some good news: The authors say the ice sheet is likely to remain stable in the short term, and if warming stays below 2 degrees Celsius by 2100, the ice sheet won’t collapse in the long run. But the study also notes that the East Antarctic Ice Sheet is already showing signs of stress from climate change and the time to act is running out. Letting the world warm beyond the limits of the Paris Agreement, study finds, could mean East Antarctica’s ice sheet could raise sea levels by as much as 3 to 10 feet (1 to 2 meters) by 2300 .
“The main conclusion of our work is that if we can comply with the Paris climate agreement, we can almost certainly avoid a large sea-level contribution from East Antarctica,” Stokes said. “So I think that among all the doomsday scenarios we’re hearing, our study offers at least some hope that we have a slim chance of protecting this ice sheet in the coming decades. As we conclude in the newspaper: the fate of the largest ice sheet in the world is in our hands.”
While these two articles cover different scenarios, the message is clear: Seriously curbing global warming is critical to keeping us all afloat.
“Antarctica is changing. The ice shelves are falling apart and sea levels are rising in response,” says Greene. “But as the Stokes et al. paper puts it so well, there is still time to act.”
