If greenhouse gas emissions continue apace, Greenland and Antarctica’s shrinking ice sheets could together contribute more than 15 inches (38 centimeters) of global sea level rise by 2100, a new study warns.
That’s beyond the amount Earth’s warming climate has already set in motion.
The findings are in line with projections in the Intergovernmental Panel on Climate Change’s (IPCC) 2019 Special Report on oceans and the cryosphere. Meltwater from ice sheets contribute about a third of the total global sea level rise. The IPCC report projected that Greenland would contribute 3.1 to 10.6 inches (8 to 27 cm) to global sea level rise between 2000-2100 and Antarctica could contribute 1.2 to 11 inches (3 to 28 cm).
The new results in the journal The Cryosphere come from the Ice Sheet Model Intercomparison Project (ISMIP6) led by NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The study is one of many efforts to project the impact of a warming climate on melting ice sheets, understand its causes, and track sea level rise.
“One of the biggest uncertainties when it comes to how much sea level will rise in the future is how much the ice sheets will contribute,” says Sophie Nowicki, professor in the geology department at the University at Buffalo. “And how much the ice sheets contribute is really dependent on what the climate will do.”
“The strength of ISMIP6 was to bring together most of the ice sheet modeling groups around the world, and then connect with other communities of ocean and atmospheric modelers as well, to better understand what could happen to the ice sheets,” says Heiko Goelzer, a scientist at Utrecht University in the Netherlands, now at NORCE Norwegian Research Centre in Norway. Goelzer led the Greenland ice sheet ISMIP6 effort.
Two shrinking ice sheet scenarios
With warming air temperatures melting the surface of the ice sheet, and warming ocean temperatures causing ocean-terminating glaciers to retreat, Greenland’s shrinking ice sheet is a significant contributor to sea level rise. Researchers investigated two different scenarios the IPCC has set for future climate to predict sea level rise between 2015 and 2100: one with carbon emissions increasing rapidly and another with lower emissions.
In the high emissions scenario, they found that the Greenland ice sheet would lead to an additional global sea level rise of about 3.5 inches (9 cm) by 2100. In the lower emissions scenario, the loss from the ice sheet would raise global sea level by about 1.3 inches (3 cm).
This is beyond what is already destined to be lost from the ice sheet due to warming temperatures between pre-industrial times and now; previous studies have estimated that contribution to global sea level rise by 2100 to be about a quarter-inch (6 millimeters) for the Greenland ice sheet.
Large loss of sea ice
The team also analyzed the Antarctic ice sheet to understand how much ice melt from future climate change would add to sea level rise, beyond what recent warming temperatures have already put in motion.
Ice loss from the Antarctic ice sheet is more difficult to predict: In the west, warm ocean currents erode the bottom of large floating ice shelves, causing loss; while the vast East Antarctic ice sheet can gain mass, as warmer temperatures cause increased snowfall.
The results point to a greater range of possibilities, from ice sheet change that decreases sea level by 3.1 inches (7.8 cm), to increasing it by 12 inches (30 cm) by 2100, with different climate scenarios and climate model inputs. The regional projections show the greatest loss in West Antarctica, responsible for up to 7.1 inches (18 cm) of sea level rise by 2100 in the warmest conditions, according to the research.
“The Amundsen Sea region in West Antarctica and Wilkes Land in East Antarctica are the two regions most sensitive to warming ocean temperatures and changing currents, and will continue to lose large amounts of ice,” says Hélène Seroussi, an ice scientist at NASA’s Jet Propulsion Laboratory in Southern California who led the Antarctic ice sheet modeling in the ISMIP6 effort.
“With these new results, we can focus our efforts in the correct direction and know what needs to be worked on to continue improving the projections.”
Different groups within the ISMIP6 community are working on various aspects of the ice sheet modeling effort. All are designed to better understand why the ice sheets are changing and to improve estimates of how much ice sheets will contribute to sea level rise.
“It took over six years of workshops and teleconferences with scientists from around the world working on ice sheet, atmosphere, and ocean modeling to build a community that was able to ultimately improve our sea level rise projections,” Nowicki says. “The reason it worked is because the polar community is small, and we’re all very keen on getting this problem of future sea level right. We need to know these numbers.”
The new results will help inform the sixth IPCC report scheduled for release in 2022.
Source: University at Buffalo
“One of the biggest uncertainties when it comes to how much sea level will rise in the future is how much the ice sheets will contribute,” says Sophie Nowickilo. “And how much the ice sheets contribute is really dependent on what the climate will do.”