Sea level rise ‘projections’ can serve as a way to stir up anxiety in populated coastal areas, but don’t seem to deter wealthy IPCC-supporting advocates of human-caused climate problems from spending large sums on beachfront property, or governments of supposedly endangered tropical islands from going ahead with new airports to boost tourism. A researcher commented on a specific IPCC ‘projection’: “When we use a rate that is better constrained by physics, we see that ice cliff instability never kicks in.”
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A new Dartmouth-led study…reports that one of the very worst projections of how high the world’s oceans might rise as the planet’s polar ice sheets melt is highly unlikely—though it stresses that the accelerating [Talkshop comment – evidence?] loss of ice from Greenland and Antarctica is nonetheless dire, says Phys.org.
The study challenges a new and alarming prediction in the latest high-profile report from the United Nations’ Intergovernmental Panel on Climate Change (IPCC) to evaluate the latest climate research and project the long- and near-term effects of the climate crisis.
Released in full last year, the IPCC’s sixth assessment report introduced a possible scenario in which the collapse of the southern continent’s ice sheets would make Antarctica’s contribution to average global sea level twice as high by 2100 than other models project—and three times as high by 2300.
Though the IPCC designated this specific prediction as “low likelihood,” the potential of the world’s oceans rising by as much as 50 feet as the model projects earned it a spot in the report.
At that magnitude, the Florida Peninsula would be submerged, save for a strip of interior high ground spanning from Gainesville to north of Lake Okeechobee, with the state’s coastal cities underwater.
But that prediction is based on a new hypothetical mechanism of how ice sheets—the thick, land-based glaciers covering polar regions—retreat and break apart. The mechanism, known as the Marine Ice Cliff Instability (MICI), has not been observed and has so far only been tested with a single low-resolution model, the researchers report in the journal Science Advances.
The researchers instead test MICI with three high-resolution models that more accurately capture the complex dynamics of ice sheets. They simulated the retreat of Antarctica’s Thwaites Glacier, the 75-mile-wide ice sheet popularly nicknamed the “Doomsday Glacier” for the accelerating rate at which it is melting and its potential to raise global sea levels by more than two feet.
Their models showed that even the imperiled Thwaites is unlikely to rapidly collapse during the 21st century as MICI would predict.
Mathieu Morlighem, a Dartmouth professor of Earth sciences and the paper’s corresponding author, said that the findings suggest that the physics underlying the extreme projection included in the IPCC report are inaccurate, which can have real-world effects.
Policymakers sometimes use these high-estimation models when considering the construction of physical barriers such as sea walls or even relocating people who live in low-lying areas, Morlighem said.
“These projections are actually changing people’s lives. Policymakers and planners rely on these models and they’re frequently looking at the high-end risk. They don’t want to design solutions and then the threat turns out to be even worse than they thought,” Morlighem said.
“We’re not reporting that the Antarctic is safe and that sea-level rise isn’t going to continue—all of our projections show a rapid retreat of the ice sheet,” he continues.
“But high-end projections are important for coastal planning and we want them to be accurate in terms of physics. In this case, we know this extreme projection is unlikely over the course of the 21st century.”
Full article here.
via Tallbloke’s Talkshop
August 22, 2024 at 05:52AM
Iowa Climate Science Education 