The Greenland ice sheet is on track to lose mass at about four times the fastest rate observed over the past 12,000 years. At its current trajectory, such melting would dump huge quantities of freshwater into the sea, raising global sea levels and disrupting ocean currents, scientists concluded in new research Wednesday.
The new findings, published in the journal Nature, warn that the only way to avoid a drastically accelerated meltdown of the ice sheet in coming decades is for the global community to curtail emissions of greenhouse gases in the near-term.
Greenland is already the largest contributor to sea level rise, though Antarctica has the potential to increase sea levels even more. As sea levels creep upward, coastal storms including hurricanes and nor'easters become more destructive. Recent trends in more frequent "sunny day flooding" at high tide in places such as Annapolis, Md.; Norfolk, Va.; Charleston, S.C.; and Miami is also linked to sea level rise.
Researchers found that the current rate of mass loss from the Greenland ice sheet is already comparable to that seen at the end of the last ice age, during a geological period known as the early Holocene. At that time, the global average surface temperature was about 5.4 degrees Fahrenheit above the preindustrial average, a temperature the world is on track to exceed by the end of this century, depending on rate of global emissions.
"It is no secret that the Greenland Ice Sheet is in rough shape and is losing ice at an increasing rate," Jason Briner, a geology professor at the University at Buffalo and lead author of the new study, said in a news release. "I think this is the first time that the current health of the Greenland Ice Sheet has been robustly placed into a long-term context."
Briner and colleagues were able to put together an unbroken history of the Greenland ice sheet's mass change, relying on computer modeling and field research in southwestern Greenland.
The researchers' projections show that after little change in ice mass loss over thousands of years, a sudden, precipitous uptick occurred in recent decades. They also project that this steep rise is to accelerate through 2100, if the world fails to drastically cut the greenhouse gas emissions fueling the globe's warming.
According to the study, the current mass loss rate of about 6.7 billion tons per century that occurred between 2000 and 2018 is comparable to rates in the early Holocene. But, depending on greenhouse gas emissions in the next few decades, future mass loss will be far more devastating -- on the order of 9.7 billion tons to 39.5 billion tons over the rest of the century.
"We're basically committed to losing ice at a faster clip than we did at that last period of rapid loss 12,000 years ago," Briner said in an interview, "and that was for me a surprising finding."
For the research, scientists relied on analyzing clues to the ice sheet's past movement by studying the chemical composition of boulders that sit on large piles of debris located at the former edge of a glacier or ice sheet, known as moraines. The analyses enabled the scientists to determine when the ice was there and when it retreated from the boulders.
The scientists compared their computer modeling results with the field work results to determine the accuracy of their projections into the future.
An "aspect I like about this study is they really attempt to set present observed changes into a longer term context to show that at present we are much closer in terms of ice sheet melt to the Holocene thermal optimum than at any other period in the last 12,000 years," said Ruth Mottram, a glaciologist at the Danish Meteorological Institute, in an email. Mottram was not involved in the new study.
Marco Tedesco, a researcher at the Lamont-Doherty Earth Observatory of Columbia University and adjunct scientist at the NASA Goddard Institute for Space Studies, called Wednesday's study "super interesting," but equally troubling.
"To my knowledge, it's the first evidence that shows that we are reaching levels of mass loss that are comparable to what happened last time when things were, so to say, bad -- meaning massive sea level rise," he said of the study, in which he was not involved.
Tedesco agreed that an unprecedented reduction in global emissions -- along with aggressive investment in capturing and sequestering carbon dioxide that already is in the atmosphere -- is the only opportunity to slow the rapid warming of the Arctic and the consequences that would bring.
"Imagine yourself with wide open arms in front of a tsunami and trying to stop it," he said.