The Antarctic ice sheet is of vital importance to the climate. Ice reflects sunlight, keeping the planet cool. The sheet contains 70 percent of all the freshwater on the planet, which, if it were to melt entirely, would absorb heat and cause global sea levels to rise by around 200 feet.

A new modeling study of the Antarctic ice sheet by scientists from the Scripps Institution of Oceanography at University of California, San Diego (UCSD), suggests that, as water beneath the glaciers melts and flows out to sea, it causes ice to melt faster, a press release from UCSD said. The process is known as subglacial discharge.

The simulation by the model suggests this meltwater effect is enough to cause significant global sea-level rise in scenarios of high greenhouse gas emissions.

Current models being used to generate major projections of sea-level rise, like those by the Intergovernmental Panel on Climate Change, are not taking the extra ice loss from the meltwater into account.

If the meltwater process is determined to be a key driver of Antarctic ice sheet loss, current projections could be underestimating the rate of sea-level rise all over the world.

“Knowing when and how much global sea-level will rise is critical to the welfare of coastal communities. Millions of people live in low-lying coastal zones and we can’t adequately prepare our communities without accurate sea-level rise projections,” said Tyler Pelle, lead author of the study and a postdoctoral researcher at Scripps, in the press release.

The study, “Subglacial discharge accelerates future retreat of Denman and Scott Glaciers, East Antarctica,” was published in the journal Science Advances.

For the study, researchers simulated the glacial retreat of two East Antarctic glaciers — Denman and Scott — through 2300 using various emissions scenarios, then applied the contributions to sea-level rise, the press release said.

The Denman and Scott glaciers combined have enough ice to cause sea levels to rise nearly five feet. In a scenario with high emissions stemming from no new climate policy that results in 20 percent higher carbon emissions by 2100, sea-level rise from subglacial discharge increased by 15.7 percent, from 0.74 inches to 0.86 inches by 2300.

The two glaciers sit next to each other on top of a continental trench with a depth of more than two miles. Once the glaciers’ retreat reaches the top of the trench’s slope, their sea-level rise contribution is predicted to accelerate considerably.

When subglacial discharge was taken into account, the model calculated that the two glaciers retreated past the slope approximately 25 years earlier.

“I think this paper is a wake up call for the modeling community,” said Jamin Greenbaum, study co-author and researcher at the Scripps Institute of Geophysics and Planetary Physics, in the press release. “It shows you can’t accurately model these systems without taking this process into account.”

Greenbaum said one of the main things to take away from the study, other than the importance of subglacial discharge in the speeding up of sea-level rise, is how important what humans do to curb greenhouse gas emissions is for the future. When the model was given a low emissions scenario the glaciers did not retreat all the way into the trench, thus avoiding breakaway contributions to rising sea levels.

“If there is a doomsday story here it isn’t subglacial discharge,” Greenbaum said in the press release. “The real doomsday story is still emissions and humanity is still the one with its finger on the button.”

And meltwater isn’t only occurring with the Denman and Scott glaciers.

“Subglacial meltwater has been inferred beneath most if not all Antarctic glaciers, including Thwaites, Pine Island, and Totten glaciers,” Pelle said in the press release. “All these glaciers are retreating and contributing to sea-level rise and we are showing that subglacial discharge could be accelerating their retreat. It’s urgent that we model these other glaciers so we can get a handle on the magnitude of the effect subglacial discharge is having.”

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