If human societies don’t sharply curb emissions of greenhouse gases, Greenland’s rate of ice loss this century is likely to greatly outpace that of any century over the past 12,000 years, a new study concludes.
University of Washington scientists are among the authors of the study published in the journal Nature. The research, led by the University at Buffalo, employed ice sheet modelling to understand the past, present and future of the Greenland Ice Sheet.
Scientists used new, detailed reconstructions of ancient climate to drive the model, and validated the model against real-world measurements of the ice sheet’s contemporary and ancient size.
The findings place the ice sheet’s modern decline in historical context, highlighting just how extreme and unusual projected losses for the 21st century could be.
“Basically, we’ve altered our planet so much that the rates of ice sheet melt this century are on pace to be greater than anything we’ve seen under natural variability of the ice sheet over the past 12,000 years. We’ll blow that out of the water if we don’t make severe reductions to greenhouse gas emissions,” said lead author Jason Briner at the University at Buffalo.
The multidisciplinary team, largely funded by the National Science Foundation, used a state-of-the-art ice sheet model to simulate changes to the southwestern sector of the Greenland Ice Sheet, starting from the beginning of the Holocene epoch some 12,000 years ago and extending 80 years into the future, to 2100.
Scientists tested the model’s accuracy by comparing the results of the model’s simulations to historical evidence. The modelled results matched up well with data tied to actual measurements of the ice sheet made by satellites and aerial surveys in recent decades, and with fieldwork identifying the ice sheet’s ancient boundaries.
“This study shows that even with uncertainties accounted for, current ice loss from Greenland is about as high as it has ever been in thousands of years, and the ice loss is increasing,” said co-author Eric Steig, a UW professor of Earth and space sciences. “We will enter a unique time within this century, if we have not already done so, for Greenland ice loss at any time in the past 12,000 years.”
Though the project focused on southwestern Greenland, research shows that changes in the rates of ice loss there tend to correspond tightly with changes across the entire ice sheet.
“We relied on the same ice sheet model to simulate the past, the present and the future,” says co-author Jessica Badgeley, a UW doctoral student in Earth and space sciences. “Thus, our comparisons of the ice sheet mass change through these time periods are internally consistent, which makes for a robust comparison between past and projected ice sheet changes.”
Steig, Badgeley and co-author Gregory Hakim, a UW professor of atmospheric sciences, combined models and records from Greenland ice cores to determine how snow accumulation and temperature have changed in the region from 12,000 years ago to the year 1850.
Those data were used to drive the ice sheet modelling, led by researchers at the University of California, Irvine and NASA’s Jet Propulsion Laboratory. Previously published climate data was used to drive the more recent simulations.
Working with scientists from the University at Buffalo and Columbia University, Badgeley helped collect lake sediment and rock samples from three locations between Nuuk, the capital of Greenland on the southwestern coast, up to the current edge of the Greenland Ice Sheet.
“We built an extremely detailed geologic history of how the margin of the southwestern Greenland Ice Sheet moved through time by measuring beryllium-10 in boulders that sit on moraines,” says co-author Nicolás Young, an associate research professor at Columbia University’s Lamont-Doherty Earth Observatory. “Moraines are large piles of debris that you can find on the landscape that marks the former edge of an ice sheet or glacier. A beryllium-10 measurement tells you how long that boulder and moraine have been sitting there, and therefore tells you when the ice sheet was at that exact spot and deposited that boulder.
“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,” Young said.
Despite the alarming results, one vital takeaway from the model’s future projections is that it’s still possible for people and countries around the world to make an important difference by cutting emissions, Briner said. Models of various scenarios yield very different results, with high-emission scenarios producing massive declines in the ice sheet’s health, and significant sea-level rise.
“This study shows that future ice loss is likely to be larger than anything that the ice sheet experienced in the Holocene — unless we follow a low-carbon emission scenario in the future,” Badgeley said.
Source: University of Washington