Antarctic ice loss tripled – should we be worried?
By Dana Nuccitelli, CCL Science Policy Network Team
A new study finding that the rate of Antarctic ice loss has tripled recently made big news. Specifically, the scientists found that the ice loss in Antarctica from 2012 to 2017 was three times larger than the ice loss from the 1990s to the 2010s. It’s a scary-sounding statistic, but how worried should we be?
That’s a difficult question to answer. Sea level rise has also accelerated in recent years due to the increase in melting ice. Since the 1990s until the 2010s, about 40% of sea level rise was due to thermal expansion (water expanding as it warms). That’s now down to 30% because melting ice is contributing more and more to sea level rise.
For example, Greenland only contributed about 5% to sea level rise in 1993; now that’s up to 25%. Glacier melt is now up from 20% to about 25% of sea level rise too. The big news from Antarctica brings its contribution up from about 6% to 20% of global sea level rise.
Overall, the rate of sea level rise has accelerated from 1.4 millimeters per year (mm/yr) in the first half of the 20th century to 3.2 mm/yr since the 1990s, and now to 4.5 mm/yr since 2012. That acceleration is due to the increase in melting ice.
Scientists don’t know how fast Antarctic ice loss will proceed. So far, the vast majority has come from West Antarctica, while East Antarctica has remained stable. That’s because about 75% of the glaciers in West Antarctica are grounded below sea level, compared to just 35% in East Antarctica. Warming ocean waters are melting the Antarctic ice from below, which is particularly problematic for that low-lying ice in West Antarctica. Research suggests that the climate has already passed a tipping point and the collapse of the Western Antarctic ice sheet is now unstoppable.
We also know that in past eras with climates similar to today’s and to the Paris climate target, like in the last interglaciation and the Pliocene, sea levels were about 20 to 80 feet higher. Unless we manage to actually cool global temperatures, we’re certainly due for significantly more sea level rise. The large ice sheets on Greenland and Antarctica will continue to melt for as long as 1,000 years. That’s why sea levels were so much higher in past eras whose climates remained at hot temperatures like today’s for thousands of years.
The question is just how fast they’ll rise, and scientists don’t yet have a good answer. The accelerated ice melt in both Greenland and Antarctica is an ominous sign, and there have been periods in the past when sea level rose as fast as 1 meter every 20 years due to rapidly melting ice. Scientists are making progress on understanding the physics of ice sheet melting, but since modern climate change is happening so fast (geologically speaking), we don’t yet have a complete understanding about how it will play out.
As James Hansen has noted, there’s been about a 100- to 400-year lag before sea level has responded to past natural climate changes, but the current human influence on the climate is much bigger than natural effects, so it could happen even faster this time around. Hansen argues that we should try to restore atmospheric carbon dioxide levels to 350 parts per million (ppm) this century if possible. For perspective, levels are currently at about 410 ppm, and to meet the Paris climate target, we need to keep them below about 450 ppm. Carbon dioxide levels are still rising at a rate of 2 to 3 ppm per year, so urgent action is needed. To limit sea level rise, we not only have to stop putting more carbon pollution into the air, but we’ll also have to start pulling a lot of carbon dioxide out of the atmosphere starting around mid-century at the latest.
Of course, as Rear Admiral David Titley says, we need to act even if we have incomplete information. For CCL, that means getting a carbon fee and dividend policy in place so that we can start cutting carbon pollution ASAP. The accelerated Antarctic ice loss and sea level rise make the urgency of that mission clear.
Dana Nuccitelli is an Environmental Scientist and writes about climate change for The Guardian and Skeptical Science.
The Science Policy Network is a team of CCL leaders and supporters with a diverse background in the field of climate science. These network contributors write regular guest posts, offering thorough insight into topics that fall within their expertise. This post and other resources are available in the form of white papers on CCL Community.