Antarctica

About 90% of our planet’s ice is located on this frigid continent, the coldest and windiest place on Earth. The Transantarctic Mountain range divides Antarctica and its 40-million-year-old coating of ice into two major sections. The West Antarctic Ice Sheet has been losing mass in recent years, as rising air and ocean temperatures erode its glaciers and ice shelves. Meanwhile, the larger, higher, and colder ice sheet over East Antarctic has been gaining mass, most likely because of a slight increase in snowfall.

Overall, Antarctica is now losing mass, as the increasing ice loss from glaciers and ice shelves in West Antarctica is more than counterbalancing the added snowpack in East Antarctica. The continent as a whole lost nearly five times as much ice from 2002 to 2011 than it did in the prior decade, according to the IPCC. The continent’s most vulnerable spot is the Antarctic Peninsula, which juts from West Antarctica toward South America. A breeding ground and home base for a wide array of wildlife, including seabirds, seals, and penguins, the Antarctic Peninsula has been warming faster than just about any place on Earth in recent decades.

The ice shelves that extend from Antarctica into the Southern Ocean are a particular concern in a warming climate. Because ice is less dense than water, these shelves do not add directly to sea level when they melt. However, the ice shelves do act as a backstop to help keep glaciers from sliding off the Antarctic continent, so any erosion of the shelves can allow glaciers to head more rapidly into the sea. After the 2002 breakup of the Larsen B ice shelf off the Antarctic Peninsula, glaciers flowing into the ice shelf started moving at eight times their normal speed.

Temperatures have shown little warming over central Antarctica in recent decades, but they are expected to rise across the continent as this century unfolds, especially as the seasonal ozone hole over Antarctica gradually diminishes. (The ozone hole has led to colder stratospheric temperatures over the continent, helping tighten the polar vortex that keeps frigid winter air locked over the continent.) Melting across the continent could increase later this century as temperatures rise, but snowfall may also increase. A far bigger concern is the potential decay of ice shelves, which in turn may leave large ice cliffs along the shoreline vulnerable to collapse. A major study in 2016 found that this process could potentially lead to a sea level rise of as much as 5 to 6 feet by 2100 — far larger than earlier estimates.