But what experts have less information on is how these vital glaciers have changed in the past, particularly in the centuries before satellite records existed. Understanding how glaciers have responded to past changes in climate can impact projections scientists make about how they may respond to future warming.
The researchers found that Greenland’s glaciers are very sensitive to climate conditions, and have lost ice in the late-19th and early-20th century at rates that rival or surpass those seen today. With the planet — and the Arctic in particular — expected to warm much more this century, the scientists warn their findings show that ice loss on Greenland could exceed even the worst-case projections.
David Holland, a professor of mathematics and environmental science at New York University and a co-author of the study, said the team’s findings show that the Arctic “is undergoing a one-two punch with respect to the loss of its land and sea ice covers in a warming world.”
Using historical photographs of the Jakobshavn, Helheim and Kangerlussuaq glaciers, the team calculated ice loss from 1880 to 2012. They estimated that the amount of ice lost from these three glaciers alone resulted in a sea level rise of 8.1 millimeters. Holland said that while the three glaciers are important in their own right, they also serve as proxies for the majority of the other outlet glaciers in Greenland, giving scientists a glimpse at how the entire ice sheet behaves.
Greenland’s ice sheet is a dynamic place that is constantly shifting and moving. If we think of the interior of the ice sheet as a mountain lake, Moon says, these outlet glaciers are the streams fanning out from the lake, carrying ice away from it and in many cases, into the ocean. When ice breaks off from the glacier and lands in the ocean, it raises sea levels.
“These three glaciers are among the fastest moving in Greenland. When we think about these glaciers all around the edge of Greenland acting like conveyor belts (moving ice towards the ocean), these are some of the fastest, largest conveyor belts on the ice sheet,” said Twila Moon, deputy lead scientist at the National Snow and Ice Data Center in Boulder, Colorado, who wasn’t involved in the study.
The glaciers also hold enough ice to raise global sea levels by roughly 1.3 meters.
Ice loss over time is driven by natural shifts in winds and ocean currents, and when warm waters get near the glaciers, they melt, Holland says. But human-caused warming has altered the climate and is changing how the winds and ocean interact with the ice sheet, and therefore influencing the amount of ice loss.
The team found that rates of ice loss for the Jakobshavn Glacier in the early 1900s were comparable to the huge rates of loss seen today, and for the Kangerlussuaq Glacier, ice loss between 1880 and 1930 was actually larger than present day.
That’s significant because it shows that the glaciers were losing large amounts of ice at a time when global temperatures were lower than they are now.
Under a worst case-scenario in which humans continue to raise concentrations of these heat-trapping gases in the atmosphere, the planet could warm by 3.7 degrees Celsius (6.66 degrees Fahrenheit) by the end of this century.
If the glaciers have already suffered large ice losses when atmospheric and ocean temperatures were lower — and the planet is set to warm even more under a high-emissions future — the scientists say their findings could mean models used to predict future ice loss in Greenland could be underestimating how much will be lost by the end of the century.
That could also impact current projections of sea level rise.
“I think when it comes to the pace of change in Greenland and really with ice everywhere in the world, we’re already at five-alarm status,” said Moon. “And this paper is one more paper in that monstrous pile that says these are really serious changes, they’re happening very quickly and we we need to be taking action as soon as possible so that we can try to reduce the rate of change in the future.”
In the study, the scientists said that the possible underestimation of ice loss is likely “not limited to just these three glaciers,” and that it was important that models capture rapid glacial retreat as a result of human-induced warming of our oceans and atmosphere “as they are the primary driver of mass loss.”
The team hopes their findings on how glaciers are sensitive to changes in the climate will help increase the reliability of future projections of ice loss.
“The Arctic is losing ice, and as you look in greater detail over the last century, you see periods of more loss and less loss, but always loss,” Holland said. “With increased warming projected to continue into the future, increased ice loss can be expected with potentially serious negative consequences for coastal cities around the world.”
CNN’s Ivana Kottasova contributed to this report.