Rick Aster has spent a career checking up on his favorite patient, the Antarctic ice sheet. Lately, the Colorado State University seismologist is worried about the patient’s weight loss.
A little slimming amid the constant pressure of global warming could be OK — West Antarctica has an unusual rock underlay that could moderate ice melt. Even at the current rate of 150 billion tons of ice per year.
But what Aster and his colleagues have confirmed recently is that Antarctic melting could accelerate in a so-called feedback loop, overflowing the continental rock “bowl” holding in a massive glacier and letting in seawater that will make the ice sheet melt even faster.
The Antarctic seismology researchers have also learned more about the gravitational pull of all that fragile ice, and how up to now it’s saved much of Earth’s coastline from further disaster. The mass has acted like a magnet, pulling liquid water up and around the Antarctic in a thicker layer than natural sea level would dictate. That kept water levels down at coastal cities to the north, from Miami to San Diego to Honolulu.
If West Antarctica keeps melting at current rates, this pull is gone, said Aster, co-author of a sea level study published this month in Science Advances. That means even more coastal inundation on the other continents.
The Antarctic glaciers alone could raise sea levels in North America by 10 feet by 2150, Aster said. Add in the melting glaciers of Greenland, the world’s second largest ice store, and there’s a world of trouble unless humans slow down climate change, Aster said. If we do, the Antarctic’s contribution to rising seas could be limited to just a fraction of that, the new study shows.
Scientists have sometimes comforted themselves with the knowledge that Earth has been through everything before. The West Antarctic ice sheet was nearly gone in the warm period before the last ice age, Aster noted. Continents survived.
“What’s really different in terms of today’s global warming, and different than anything that the Earth has seen as far as we know,” Aster added, “is the rapidity of human-caused climate change. We’re spiking the carbon dioxide and otherwise changing the climate so rapidly that we’re in territory where it’s hard or impossible to find natural analogs that we can study in Earth’s past history.”
Geologic time goes by in ticks of thousands or millions of years; climate change time appears to be passing in mere double digits.
“It’s happening so rapidly that we can see these large effects even in a human lifetime,” Aster said. “And that is something that the Earth has not seen before, as far as we know. So that’s the most stunning thing to me.”
The study directs a spotlight toward global warming in real time. The Earth actually is melting, at an accelerated pace that has geologists accustomed to thinking in 100,000-year blocks now measuring change at the 100-year level.
Aster and team’s contributions to the study are not directly aimed at ice melt itself, but what happens to the geology underneath underneath when that snowcap disappears. Simplified answer: The rock pushes up under the reduced pressure and slows the loss of ice to the sea. The team found that parts of the bedrock in West Antarctica, the area below South America, are rising at about 2 inches a year as it sheds ice, among the fastest rates on earth.
Wait, that could be good, right? A self-correcting problem? As the seas rise and threaten coastlines, the coastline itself rising up could solve that? Correct, Aster says, but only if the melt is held to a low or moderate level. At the current glacier-gushing rates, the “float” of continental rock can’t keep up with the fast rise of sea water.
At the higher rates of melt, North America will see its ankles — Miami and New Orleans — inundated within our lifetime unless temperatures are stabilized.
If humans slow global warming, the West Antarctic Ice Sheet can substantially stay in place and help reduce the worst-case sea level rise attributed to the Antarctic by 40%, the study says.
“Earth uplift can be our friend and the Earth’s friend, if we don’t ask too much of it,” Aster said.