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Why climate change models are wrong, according to bombshell study
A new analysis shows the 'worst case scenario' for Antarctica's melting glaciers is much less severe than the United Nation's current estimates.
The UN's prediction that the melting of Antarctica's so-called 'Doomsday' glaciers could alone raise global sea levels two feet before the year 2100 has shaped global climate policy since at least 2016, when the estimate was first introduced.
The model — which the UN Intergovernmental Panel on Climate Change (IPCC) does admit is 'low likelihood' — projects this melt could raise sea levels up 50-ft by 2300.
But three new, more sophisticated climate models, produced with the backing of the National Science Foundation, now call this UN glacier model 'extreme' and 'unlikely.'
More realistic new scenarios, revealed by these new 'ice melt' simulations, predict the glaciers are not likely to break apart in the feared, cascading chain-reaction.
Researchers (boat, bottom left) map geothermal heat flows off West Antarctica in August 2021. Ice losses from Thwaites Glacier in that region has been responsible for roughly four percent of the global sea-level rise - but new models suggest a worse case scenario is unlikely
Above, Thwaites Glacier (mapped, in red) is defined as the region between Ellsworth Land and Marie Byrd Land. It's one key vulnerable part of the West Antarctic Ice Sheet
'We're not reporting that the Antarctic is safe and that sea-level rise isn't going to continue,' study co-author and earth sciences professor Mathieu Morlighem said.
'All of our projections show a rapid retreat of the ice sheet,' he emphasized.
What Morlighem and his co-authors did do was focus their modeling on the polar continent's 'Doomsday Glacier,' the Thwaites Glacier: a 75-mile-wide, heavily monitored plateau of ice whose collapse could swell oceans catastrophically.
What they hoped to test is whether or not the disappearance of massive portions of this glacier's floating outermost edge, its ice shelf, could trigger a the sliding of Antarctica's land-locked ice into the ocean — where it would raise sea levels rapidly.
'High-end projections,' like IPCC's worst case scenario, Morlighem said, 'are important for coastal planning and we want them to be accurate in terms of physics.'
A dramatically high and unlikely scenario, in other words, could lead a city council in Miami to waste taxpayer money on sea walls that are much higher than needed.
'These projections are actually changing people's lives,' Morlighem noted.
Above a model of the processes impacting how this 'Doomsday Glacier' may behave as it melts
Above, an aerial photo of the Thwaites Glacier's ice shelf. Climate scientists have long worried that removal of this ice shelf, under certain conditions, could lead to massive amounts of ice from the polar continent spilling into the ocean - with drastic implications for global sea levels
This worst case scenario from UN's IPCC report is based on a scenario where humanity's population and its burning of coal both continue to dramatically increase alongside 'business as usual' for the rest of the globe's fossil fuel use.
Scientists have named this 'high emissions' future scenario RCP8.5.
Dr Detlef van Vuuren, a Dutch chemist and IPCC environmental scientist, has described RCP8.5 as 'a possible no-climate policy world.'
It presumes about 8.5 watts-per-meter-squared (W/m2) of radiated heat from greenhouses gases above pre-industrial levels.
'It is important to have a high-end baseline scenario to explore what "could" happen,' as Dr va Vurren told Carbon Brief.
'And really, forcing levels of around 8.5 W/m2 are not implausible,' the scientist said.
But in RCP8.5, the IPCC's most dramatic, eye-popping worst case outlook, nearly all of Florida would be submerged in a global deluge of rising ocean tides by 2300.
The entire peninsula of the Sunshine State, save for a strip of inland high ground from Gainesville to Lake Okeechobee, would be undersea sinking coastal cities. It is, by design, in other words, the most extreme scenario possible.
'Policymakers and planners rely on these models and they're frequently looking at the high-end risk,' according to Morlighem, who researches the physics of glacier ice at Dartmouth University.
Policy-makers often want to prepare for the absolute worst: 'They don't want to design solutions and then the threat turns out to be even worse than they thought.'
The new study simulated the rate at which the Doomsday Glacier thinned (top row) and the speed at which is would slide (bottom row), in response to losing a portion of its ice shelf 'calving' into the sea. It found a lost ice shelf would not lead to the feared worst case reaction
glacier melt (above) drips into icicles off floating winter sea ice, grounded on rocks in low tide
His team developed three ice melt models capable of simulating the Thwaites Glacier's retreat at a higher resolution than the IPCC's latest low resolution model.
The new study, published Wednesday in the journal Science Advances, employed a computer model created by Dartmouth in collaboration with NASA's Jet Propulsion Laboratory and the University of California at Irvine.
The model, known as Ice-sheet and Sea-level System Model (ISSM), was capable of handling 75,000 individual elements within its simulation at a resolution of about one mile (1.5 kilometers).
Their two other simulations, were similarly complex.
One, named Úa started with initial conditions consisting of 90,000 elements, and a resolution of 0.62 miles (1 km) near the key points in need of modelling, including where the large pieces of the glacier shelf could 'calve' or break off into the sea.
The last model, called STREAMICE, also had a resolution of 0.62 miles (1 km).
All of these models predicted an instantaneous increase in flow speed of up to 3 km/year right after the initial ice shelf collapse, or a doubling of today’s ice flow speed.
The new study also simulated the rate at which the Doomsday Glacier thinned and the speed at which is would 'calve' portions of the glacier and slide those new icebergs into the sea.
But, ultimately, it found that a lost ice shelf would not lead the remaining glacier to retreat inland, nor trigger a runaway breakdown.
'Ice front retreat requires that the calving rate due to cliff failure exceeds this ice speed,' the team wrote, 'which is rarely the case in our simulations.'
But while these findings undermined the projections of the UN IPCC's models, it did not paint a completely rosy picture of planet Earth's southern-most continent.
Glaciologist Dr Dan Goldberg at the University of Edinburgh, a co-author on the new paper who was once a visiting professor at Dartmouth, noted that the Doomsday Glacier is likely to keep retreating inland in unpredictable ways past this century.
Researchers published the results of a three-year study in 2023 that deployed a yellow, pencil-shaped robot 'Icefin' (above) that looked at the forces eating away under the Thwaites glacier
'Thwaites is likely to retreat unstably in the coming centuries, which underscores the need to better understand how the glacier will respond to ocean warming and ice-shelf collapse through ongoing modeling and observation,' Dr Goldberg said.
Goldberg and Morlighem worked with Dr Hélène Seroussi, an associate professor of engineering at Dartmouth, as well as researchers from the University of Michigan, the University of Edinburgh, Northumbria University and more on this modelling.
Dr Seroussi took pains to emphasize that only one key component of the IPCC's modelling was off: how it predicted the behavior of the ice shelf of the glacier out over the open ocean, called the Marine Ice Cliff Instability (MICI) mechanism.
'We're not calling into question the standard, well-established projections that the IPCC's report is primarily based on,' Dr Seroussi said.
'We're only calling into question this high-impact, low-likelihood projection that includes this new MICI process that is poorly understood,' she emphasized.
'Other known instabilities in the polar ice sheets are still going to play a role in their loss in the coming decades and centuries,' she said.