The greenhouse gas increases over the next century could warm the Arctic by 3-5 degrees Celsius in summertime, when sea levels eventually rise up to six meters higher than today, according to a new study released on Thursday.
Arctic summers by 2100 may be as warm as they were nearly 130,000 years ago, between the most recent ice age and the previous one. At that time, significant portions of the Greenland and Antarctic Ice Sheets melted, said scientists at U.S. National Center for Atmospheric Research and the University of Arizona.
The findings were published in the March 24 issue of the journal Science.
Earlier studies have predicted that the Greenland Ice Sheet could raise the sea level by two to three meters, just like the last warm era 130,000 years ago. But contrary to what was previously believed, the study suggested the Antarctic ice sheet also melted substantially, contributing another two to three meters of sea level rise.
The ice sheets have been melting already, said the researchers. They suggested the melting could accelerate, thereby raising sea level as fast as, or faster than, about one meter of sea level rise per century.
"Although the focus of our work is polar, the implications are global," said Bette Otto-Bliesner, a co-author of the study.
"These ice sheets melted before and sea levels rose. The warmth needed isn't that much above present conditions."
Although ice sheet disintegration and the subsequent sea level rise lags behind rising temperatures, the process will become irreversible sometime in the second half of the 21st century, unless something is done to dramatically reduce human emissions of greenhouse gas pollution, according to Jonathan Overpeck, lead author of the study.
"We need to start serious measures to reduce greenhouse gases within the next decade. If we don't do something soon, we're committed to four-to-six meters of sea level rise in the future," he noted.
As sea levels rise, coastal regions are more susceptible to the impacts of storm surge. The predicted rise would eventually inundate heavily populated coastal areas worldwide, the researchers said.
The researchers used a computer model to predict future climate, and combined it with ice sheet simulations to estimate what the Earth's climate was like 129,000 years ago.
They also cross-checked the computer's estimate of ancient climate against data from natural recorders of ancient climate such as sediments, fossils and ice cores.
These studies are the first to link Arctic and Antarctic melting in the last interglacial period, said the researchers. Marine diatoms and beryllium isotopes found beneath the West Antarctic Ice Sheet indicate that parts of the ice disappeared at some point over the last several hundred thousand years.
The researchers theorized that the rise in sea levels produced by Arctic warming and melting could have helped destabilize ice shelves at the edge of the Antarctic and led to ice sheet collapse.
If such a process occurred today, it would be accelerated by global scale greenhouse-induced warming year round, while in the Arctic, melting would likely be hastened by pollution that darkens snow and enables it to absorb more sunlight.
"Even in the absence of more-realistic models of ice-sheet behavior, it remains that ice sheets have contributed meters above modern sea level in response to modest warming, with peak rates of sea-level rise possibly exceeding 1 m/century," the researchers concluded in the paper.