Are the Antarctic’s ice sheets shrinking or growing? And what does that mean for global sea-level rise?
Those questions are being hotly debated by the world’s climate scientists as global leaders prepare for the UN climate talks in Paris at the end of this month. Now, a new study by a team of NASA climate scientists has sparked controversy by reporting that “Antarctica is actually gaining ice.”
Scientists concluded in the Journal of Glaciology that the loss of glacier mass in Antarctica’s western region is being offset by thickening of glaciers on the continent’s eastern interior, which has experienced increased snowfall. The result: A net gain of about 100 billion tons of ice per year, according to the report.
That increase in ice translates to about a quarter of a millimeter per year less sea level rise than was previously predicted, says lead author Jay Zwally, chief cryospheric scientist at NASA’s Goddard Space Flight Center in Maryland.
Here’s what you need to know about the new findings:
Do prominent climate scientists agree with the primary conclusions?
No. Some leading scientists vocally disagree with the study, which also runs contrary to the prevailing view of experts that Antarctica has been losing ice mass over the past few decades.
“I think there's a serious issue with the study,” says Ted Scambos, lead scientist at the National Snow & Ice Data Center in Colorado. “It’s unfortunate that it made it through peer review.”
The paper is inconsistent with other studies that show an overall loss of ice there of around 100 billion tons, based on satellite measurements of the gravity of the ice and snow. (Learn more about climate change in the most recent cover story of National Geographic magazine.)
So what are the limitations of the NASA study?
Zwally’s team used satellites to measure the elevations of glaciers on Antarctica. But University of Washington glaciologist Ben Smith, who was not involved with the study, points out that the technology might not be up to the task of distinguishing snowpack volume based on a difference in elevation of one or two centimeters.
Scambos agrees, adding that the complex geography of some areas of Antarctica make it hard to characterize with one satellite alone.
University of Alaska, Fairbanks glaciology professor Erin Pettit calls the methodology “a really, really hard measurement that I would take with a heavy load of salt.”
If Antarctica’s ice sheets have indeed been growing overall, then why is the continent contributing to global sea level rise?
That’s a good question, says Scambos. Climate scientists have previously reported that melting ice in the Antarctic has been contributing a small amount to sea level rise over the past few decades. The exact amount is hotly debated, but it is likely on the order of a few centimeters.
If the Antarctic’s ice sheets are growing, what would that mean for global sea levels in the long-term?
“I don't think Zwally's estimates really matter so much in the grand scheme because adding a little snow to Antarctica in no way offsets the complete disintegration of the West Antarctic ice sheet in the near future,” says Pettit, who is also a National Geographic explorer who works on the continent. “It’s completely different timescale behavior.”
If all the ice in West Antarctica melts and slides into the sea, it is likely to contribute several meters to sea level rise. That process is already underway, says Scambos, and may happen over the next few centuries, regardless of what is going on in the eastern highlands.
There are too many different lines of evidence and active inquiry “to let one paper hold sway,” says Scambos. The consensus view seems to be that Antarctica is experiencing melting in important ways and will likely contribute more to sea level rise in the coming centuries.
So global warming still exists?
Yes. The new paper never says the planet isn’t warming. The best science available on the long-term trends still makes a strong case for that, with significant implications for the planet. Exactly how global warming will play out on every corner of the globe is largely unknown.