Greenland and Antarctica are seeing faster than expected warming that triggers glacial quakes and has the potential for a sharp rise in sea levels, according to three peer-reviewed studies published Thursday.
Warming temperatures are causing glaciers the size of Manhattan to trigger quakes, and computer models indicate that by 2100 the poles could be as warm as they were 129,000 years ago — when melting ice sheets caused sea levels to rise up to 20 feet (6 meters) higher than today.
The studies didn’t predict how much sea levels might rise by 2100, but the work shows warming at a faster rate than estimated by the U.N. climate body, which expects up to a 34-inch (88-centimeter) rise by 2100.
The comparison to 130,000 years ago does not mean the researchers are predicting a 20-foot ocean rise, because the warming in ancient times was caused by changes in Earth’s tilt and orbit. But even small increases would still be enough to wipe out some islands and cause massive coastal changes around the world.
“Although the focus of our work is polar, the implications are global,” Bette Otto-Bliesner, a National Center for Atmospheric Research scientist who co-wrote two of the studies, said in a statement. “These ice sheets have melted before, and sea levels rose. The warmth needed isn’t that much above present conditions.”
Computer models used
In one study, researchers used computer models of future climate as well as data from ancient ice cores and coral reefs to determine how large the Greenland ice sheet was 129,000 years ago, when sea level was 10-20 feet higher than it is today.
The team used that data to reconstruct surface temperatures back then, and estimated that the Greenland ice sheet and other arctic ice fields contributed 6 to 11 feet (2 to 3.5 meters) of sea level rise. Coral records indicate the rise could have been as high as 20 feet, leading researchers to think that Antarctic melting was reponsible for anything over 11 feet.
In the related study, researchers used the climate reconstruction and models to conclude that surface temperatures will be as much as 5 to 8 degrees Fahrenheit warmer by 2100 — as high as they were 129,000 years ago.
Otto-Bliesner said the models correctly showed how past climate had changed, and that “gives us more confidence in their ability to predict future climate change.”
Earth in the danger zone?
Greenhouse gases such as carbon dioxide are chemicals that have been increasing in the atmosphere since the Industrial Revolution, raising fears of altering the planet’s climate by trapping heat from the sun.
Earth goes through natural climate changes, but many scientists believe the greenhouse emissions from cars and industry are contributing to that.
Michael Oppenheimer of Princeton University, who was not part of the research teams, said one point that stands out is “that a modest global warming may put Earth in the danger zone for a major sea level rise due to deglaciation of one or both ice sheets.”
Some industrialized countries have signed a pact to curb greenhouse gas emissions. The United States has refused, saying the pact would weaken the U.S. economy and that it unfairly leaves out developing countries.
Recent studies have found accelerated rates of glacial retreat along the margins of both the Greenland and West Antarctic ice sheets. And earlier studies have found that sea levels have been rising at about an inch (2.5 centimeters) per decade.
Jonathan Overpeck, a University of Arizona geoscientist who co-wrote the studies with Otto-Bliesner, said it’s possible that the rise in sea levels from polar melting could have helped destabilize ice shelves at the edge of the Antarctic ice sheet and led to their collapse 129,000 years ago.
If that is happening today, he said, it would mean a faster melt because of greenhouse-induced warming as well as air pollution, which darkens snow and enables it to absorb more sunlight and thus melt faster.
The National Science Foundation financed the research, which included scientists from the universities of Calgary and Colorado, the U.S. Geological Survey and Pennsylvania State University.
In a third study in Science, researchers said glacial earthquakes in Greenland occur most often in July and August and have more than doubled since 2002.
Melting water from the surface gradually seeps down, accumulating at the base of a glacier where it can serve as a lubricant allowing the ice to suddenly move downhill, the researchers reported.
“People often think of glaciers as inert and slow-moving, but in fact they can also move rather quickly,” Goeran Ekstroem of Harvard University said in a statement. “Some of Greenland’s glaciers, as large as Manhattan and as tall as the Empire State Building, can move 10 meters in less than a minute, a jolt that is sufficient to generate moderate seismic waves.”
“Our results suggest that these major outlet glaciers can respond to changes in climate conditions much more quickly than we had thought,” added team member Meredith Nettles of Columbia University’s Lamont-Doherty Earth Observatory.
Between January 1993 and October 2005 seismometers detected 182 quakes in Greenland. All were located in valleys draining the Greenland ice sheet, and they ranged in magnitude from 4.6 to 5.1.
The journal Science dedicated its weekly editorial to the studies, stating that while humans have long felt a “sense of security” about climate, “the expectation that change is unlikely is not a reasonable position.”