Antarctica has lost nearly 3 trillion tons of ice since 1992

Antarctica is shedding ice at an increasing rate, raising global sea levels and threatening coastal cities, according to a new international assessment published in the journal Nature.

Why this matters: The safety of coastal populations, including growing megacities worldwide, is intricately tied to the fate of Antarctica's ice sheet. Until a few years ago, Antarctica was assumed to be far more stable than the Greenland Ice Sheet, but that is no longer the case.

The faster and more significantly that Antarctica melts due to global warming, the higher that seas will rise. This means more damaging storm surges and so-called "sunny day" flooding during ordinary high tides. Such flooding is already happening along the U.S. East Coast.

If all of Antarctica were to melt, the study says, it would raise global sea levels by a catastrophic 58 meters, or 190 feet. Luckily, no study is projecting this will happen, at least not anytime soon. However, greater than 1 meter, or 3.3 feet, of sea level rise is possible by the end of this century, with more to come thereafter.

What they did: An international team of 84 scientists examined more than 150 assessments of ice loss from Antarctica, incorporated the latest measurements from satellites and other methods, and arrived at a consensus view.

By the numbers: The scientists found that Antarctic ice melt is accelerating, as is the continent's contribution to global sea level rise.

• The IMBIE study found the continent has lost about 3 trillion tons of ice between 1992 and 2017, which means it has led to an increase of 7.6 millimeters of sea level rise.
• Two-fifths of the sea level rise contribution, however, took place in just the past five years.

The IMBIE team also released an assessment in 2012, but Andrew Shepherd, a researcher at the University of Leeds, told Axios in an interview that at that time, Antarctic melt was looking less serious. Things are different now, though.

“We now see that the sea level contribution has increased in the past 5 years.”

Key details: According to Pippa Whitehouse, a research fellow at Durham University in the UK, there was a three-fold increase in the average rate of mass loss between the period prior to 2012 and during the 2012-2017 period.

"This is re-writing the rule book with regard to our understanding of the processes controlling ice sheet change in Antarctica," she said in an email.

Richard Alley, a climate scientist at Penn State University who was not involved in the new studies, said its results will serve as a reference point.

"... This is the most authoritative and comprehensive treatment to date and should further reassure the public and policymakers that the science is solid, while perhaps making people more broadly less assured because the small warming and other climate changes to date have already triggered mass loss," Alley told Axios in an email.

The big picture: Two large areas of Antarctica are mainly responsible with the acceleration in ice melt: The Antarctic Peninsula and the West Antarctic Ice Sheet. In both regions, marine-terminating ice sheets are melting from above, due to warmer air temperatures, and from below due to relatively mild ocean waters that are eating away at the ice.

These ice shelves act like door stops, buttressing inland ice and preventing glaciers from flowing into the sea. Any weakening or disappearance of these ice shelves can quickly render an inland glacier unstable.

Because of the geology of the West Antarctic Ice Sheet, where inland ice actually rests on bedrock that is below sea level, the weakening of ice shelves there may already have triggered irreversible melting, previously published studies have shown.

• Consistent with this, the West Antarctic Ice Sheet saw its melt rate increase from 53 billion tonnes per year to 159 billion tonnes a year during the 1992 to 2017 period, the IMBIE study found.
• The trends in the East Antarctic Ice Sheet are less certain now, with some studies showing that area slipping into a net loss as well.

Be smart: Antarctica's future, and the future of the world's populated coastlines, are intricately linked and dependent on decisions made during the next one to two decades. It's not a done deal that huge parts of Antarctica are doomed, unless countries fail to rein in greenhouse gas emissions causing global warming.

"The results from Antarctica are a clear sign that we woke up a sleeping giant," says Eric Rignot, a senior research scientist at NASA's Jet Propulsion Laboratory and coauthor of one of the new Antarctic ice melt papers.

Now that it's awake, "We do not want the giant to start walking," he told Axios via email.

Go deeper: "Choosing the Future of Antarctica."