Melting of Antarctica is speeding up, worrying scientists


Their mission is to produce the most comprehensive look at what's happening to the world's vulnerable ice sheets in Antarctica and Greenland.

Satellites that scanned Antarctic ice with altimeters gathered evidence about its volume; another type of satellite measurement tracked the speed of glacial flow into the ocean; and a third type of observation calculated the gravity of land masses around the planet, weighing the ice sheets in their entirety.

Per the team's calculations, a high emissions scenario - in which carbon emissions rise unabated and environmental protections in Antarctica are not implemented - global air temperature would rise almost 3.5°C above 1850 levels by 2070, with sea level rise averaging somewhere between 10-15 mm every year.

It is likely natural variability, not climate change, and East Antarctica is probably going to be stable for a couple decades, said study co-author Joughin. There's another number, though, that's more pressing: how fast Antarctica is now melting. That is at the upper end of what the Intergovernmental Panel on Climate Change has estimated Antarctica alone could contribute to sea-level rise this century.

Pine Island Glacier in Antarctica is melting at an alarming rate. It also means the ice cliffs at the snout of those glaciers are getting taller and more prone to collapse.

The most complete analysis to date measuring ice sheet changes in Antarctica reveals Earth's southernmost continent has lost some 3 trillion tonnes of ice over the past quarter-century. The tally has since jumped to 0.6mm a year.

But between 2012 and 2017, the annual ice loss rate tripled to about 219 billion tons, or 0.6 millimeters of sea-level rise.

Antarctica is not the only contributor to sea-level rise.

The study also helps clear up some uncertainty that was linked to regional differences in Antarctica. The total contribution is highlighted by the bold white line, while the blue lines track the individual contributions from East Antarctic, the Antarctic Peninsula and West Antarctica.

As shown in the video above, these changes are not uniform over the entire Antarctic ice sheet.

East Antarctica has sometimes been a focus of attention for people who deny the science of global warming. Their results - known formally as the "Ice Sheet Mass Balance Inter-comparison Exercise" (IMBIE) - were published Wednesday in the journal Nature.

In a new study, the most comprehensive to date of the continent's icy status, an worldwide group of 84 researchers analyzed data from multiple satellite surveys, from 1992 to 2017.

"The satellite measurements tell us that the ice sheet is much more dynamic than we used to think", he said. "And we find that by combining all of the available measurements we can iron out the problems that individual techniques have".

The changes are largely driven by ice melt in West Antarctica, where warm ocean water can get underneath glaciers, destabilizing them. Antarctica is, on balance, losing its ice sheets and raising the world's sea levels. "But remember for the northern hemisphere, for North America, the fact that the location in West Antarctica is where the action is amplifies that rate of sea level rise by up to an about additional 25 percent in a city like Boston or NY". "Since around 2010, 2012, we can see that there's been a sharp increase in the rate of ice loss from Antarctica".

"Now when we look again, we can see actually that the signal is very different to what we've seen before", Shepherd said.

Between 1992 and 1997, it was losing ice at an average rate of 49 billion metric tons (49 gigatons) a year.

Advancements in Earth-observing satellites have enabled researchers to better understand the polar regions.

Direct observation from satellites upended that view. So we should expect "periods of stability interspersed with rapid retreat, " he said.

However, the role of sea ice in buffering ice shelves and continental ice sheets is rarely factored into Antarctic ice-loss modelling, according to lead researcher Dr Rob Massom from the Australian Antarctic Institute.

"They're melting the ice at rates that far exceed anything that would change in the air, and these are forces that you can't reverse easily".