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Ice loss from the Greenland ice sheet will contribute at least 10 inches to sea level rise, regardless of human efforts to limit global warming, according to a new study that challenges the Intergovernmental Panel on Climate Change’s (IPCC) approach to measuring the phenomenon.
“Our study takes a completely new approach—it is based on observations and glaciological theory rather than sophisticated numerical models,” writes field glaciologist and co-author Alun Hubbard for The Conversation, adding that the other models “fail to capture the emerging processes that we see amplifying Greenland’s ice loss.”
Greenland’s ice sheet is a one- to two-mile-thick frozen reservoir of freshwater that, if fully melted into the world’s oceans, would raise the global sea level by roughly 24 feet (seven metres). Though the ice sheet is not a static geologic feature—its size and volume has ebbed and flowed with climatic changes during its 2.6-million-year existence—human-induced global warming is hastening its melting rate, prompting ice loss that has contributed to 0.04 inches (0.1 centimetres) of sea level rise each year over the past decade.
Previous studies—like those reported by the IPCC—rely on complex models to project that the melting ice sheet will raise sea levels by around four inches (10 centimetres) by 2100 in a low-emissions scenario, or up to six inches (15 centimetres) in a worst-case scenario. But scientists working on the ground say those projections don’t represent what they’re witnessing first-hand, possibly because the models can’t account for nuanced variables, like how the ice sheet is affected by meltwater travelling unseen below the surface through crevasses called moulins, reports the Washington Post.
“There are also ‘unknown unknowns’—those processes and feedbacks that we don’t yet realize and that models can never anticipate,” says Hubbard. “They can be understood only by direct observations and literally drilling into the ice.”
Published in the journal Nature Climate Change, the new study takes a different approach, basing its projections on “proven glaciological theory constrained by two decades of actual measurements from weather stations, satellites, and ice geophysics,” Hubbard writes. This alternative predicts ice melt rates significantly more dramatic than those previously described, forecasting that at least 3.3% of the ice sheet will melt, raising global sea levels by at least 10 inches (25 centimetres) regardless of emissions reductions. Though it may take much longer than 80 years for this to occur, researchers say most of the change can happen before 2100.
“This ice has been consigned to the ocean, regardless of what climate [emissions] scenario we take now,” said study co-author William Colgan, a glaciologist at the Geological Survey of Denmark and Greenland.
Some experts temper this concern by noting that scientists remain uncertain about how the ice sheets will change—indicating the need for more research.
“The problems are deeply challenging, will not be solved by wishful thinking, and have not yet been solved by business-as-usual,” said Pennsylvania State University ice sheet expert Richard Alley.
But what is clear is that, the more the planet warms, the more the seas will rise, he added.
“[The] rise can be a little less than usual projections, or a little more, or a lot more, but not a lot less,” Alley said.