A new study of satellite data from NASA says that the overall ice sheet that covers Antarctica has been slowly thickening. However, the two sides of the continent are seeing contrasting effects: warming conditions in West Antarctica have been contributing to the retreat pof  the ices sheets there, and increasing the destabilization of the glaciers. Meanwhile, East Antarctica has been seeing an increase in ice thickness — which presents a new mystery to climatologists.

West Antarctica is comprised mainly of a large peninsula south of South America, that juts out further north than the rest of the continent, where it meets warmer waters than what is experienced by the rest of Antarctica, and it is also home to massive ice shelves, where the ice sheets meet the ocean. However, a new study from the Potsdam Institute for Climate Impact Research shows that warming ocean currents under the ice sheets in the Amundsen Sea have caused an unstoppable retreat, and are threatening to destabilize the continental glaciers behind the ice sheets. If the glaciers slide into the ocean, the result will be a rise in sea levels that will flood coastal areas around the world, rendering dozens of huge port cities unlivable.

“We showed that there is actually nothing that stops it,” said study co-author Anders Levermann. “There are troughs and channels and all this stuff, there’s a lot of topography that actually has the potential to slow down or stop the instability, but it doesn’t.

“The result of this study is an if–then statement, saying that if the Amundsen Sea Sector is destabilized, then the entire marine part of West Antarctica will be discharged into the ocean.” The ice sheet of Western Antarctica holds a sizable portion of the world’s fresh water ice, and could raise sea levels by 3.3 meters (10 feet) if it were to melt.

In Eastern Antarctica, the situation is the exact opposite: the ice sheet appears to be thickening there. A study recently released by NASA shows that an increase in land height on that side of the continent is due to a thickening of the ice. While this might be considered good news for rising sea levels, as this means that more of the Earth’s water is being stored there, it instead presents a mystery: it has been assumed, up until now, that Eastern Antarctica has been contributing to a 0.27  millimeter annual rise in sea levels, through melting ice. However, NASA’s new calculations show that that portion of the continent is decreasing sea levels by 0.23  millimeters per year — leaving climatologists with a disturbing question: where is the water that is contributing to the documented rise in sea levels actually coming from?

So far, that’s a mystery, but it’s one that must be solved if we are to understand and prepare for further sea level rises.