But a huge sheet of ice the size of Florida is growing unstable and could flow into the ocean sooner than expected, pushing the sea level up by another foot and a half. And this is all presuming that global temperatures stay like they are right now and don’t continue to rise.
Spoiler alert: no one expects those temperatures to stop rising anytime soon.
A new study out this week looked at potential instability within the huge Thwaites Glacier in Antarctica that could accelerate its inevitable rate of flow into the ocean.
“If you trigger this instability, you don’t need to continue to force the ice sheet by cranking up temperatures. It will keep going by itself, and that’s the worry,” said Georgia Tech professor Alex Robel, who led the NASA-funded study published in Proceedings of the National Academy of Sciences.
The instability has to do with the amount of ice that rests on the bedrock seafloor versus extending over water and contributing to sea level rise.
“Once ice is past the grounding line and only over water, it’s contributing to sea level because buoyancy is holding it up more than it was before,” Robel said. “Ice flows out into the floating ice shelf and melts or breaks off as icebergs.”
Once the ice is over water it also speeds up the process by which more ice above it flows to the sea.
“The process becomes self-perpetuating,” said NASA JPL scientist Helene Seroussi, who collaborated on the study. “After reaching the tipping point, Thwaites Glacier could lose all of its ice in a period of 150 years. That would make for a sea level rise of about half a meter (1.64 feet).”
Perhaps the most pernicious problem is that the instability within the ice sheet can make forecasting future flood risks particularly challenging.
“You want to engineer critical infrastructure to be resistant against the upper bound of potential sea level scenarios a hundred years from now,” Robel said. “It can mean building your water treatment plants and nuclear reactors for the absolute worst-case scenario, which could be two or three feet of sea level rise from Thwaites Glacier alone, so it’s a huge difference.”