(The Hill) — Four key pillars of the global climate are melting in the heat trapped by rising fossil fuel emissions, a new study has found.

The relatively stable climate that nurtured human civilization depends in large part on these structures: the ice sheets of Greenland and West Antarctica, the Amazon rainforest and the Atlantic currents that warm Europe.

Under current policies, the world faces a scenario in which those pillars have roughly even odds of either surviving or collapsing during the next three centuries, according to results published on Thursday in Nature Communications.

The scientists warned that if the pillars are fatally undermined by heat, the resulting damage could prove impossible to undo — even if temperatures are successfully brought down later in the 21st century.

Even so, the long timeline of those findings makes them, if anything, optimistic relative to other recent ones: They come on the heels of a string of disturbing studies about key global systems like the conveyor-belt Atlantic current that keeps Europe temperate, or the West Antarctic Ice Sheet that keeps global sea levels stable.

They also come as the impacts of rising heat become increasingly obvious, seen in a range of phenomena including record-breaking temperatures — such as those baking Olympic athletes in Paris — thousand-year storms and worsening harvests.

Here’s what you need to know.

What did Thursday’s study find?

The Nature study found that the four “pillars” it focused on — the Atlantic Meridional Overturning Current (AMOC), the Amazon rainforest and the vast but melting Greenland and West Antarctic Ice Sheets — are interconnected, like a row of dominoes. 

And the risk of those dominoes toppling increases with every 0.1 Celsius (about 0.2 Fahrenheit) of additional heat above the red line of 2 degrees Celsius set in the Paris climate agreement, the researchers wrote.

They found that that risk is most urgent for the Atlantic current, which could tip into collapse within the next 15 years, and the Amazon rainforest, which could begin a runaway process of conversion to fire-prone grassland by the 2070s.

“Following current policies this century would commit to a 45 percent tipping risk by 2300, even if temperatures are brought back to below 1.5 [Celsius],” they wrote.

Why is the integrity of these ‘pillars’ so important?

Because they serve as bulwarks of the modern climate.

Each of these pillars is stabilized by, and contribute to, much larger patterns in the global climate and human civilization — as well as the other pillars.

Take the AMOC: It functions as a conveyor belt that brings warm water from the tropics up into the North Atlantic, causing Europe to experience much warmer temperatures than Canada.

The current’s weakening or failure would trap more hot water in the southern ocean, generating more hurricanes and speeding the melting of the Antarctic ice sheets, and lead to something like cataclysm for European agriculture — the sort of catastrophe for which preparation is of little use.

“You cannot adapt to this,” the University of Copenhagen’s Peter Ditlevsen, who co-authored a Nature study last year on the potential midcentury collapse of the AMOC with his sister Susanne, told Inside Climate News. 

If that collapse occurs, he told Inside Climate, there are “studies of what happens to agriculture in Great Britain, and it becomes like trying to grow potatoes in Northern Norway.”

Similarly, the Amazon stabilizes global climates and regional temperatures, locking down planet-heating greenhouse gasses and generating rain that waters fields as far away as the U.S. Midwest.

And the full collapse of the cubic miles of ice in the Greenland Ice Sheet — whose melting is one of the principal sources of current sea level rise — would lead those levels to climb 23 feet, according to NASA.

How does the new study stack up against previous findings?

The Nature study builds upon prior research that suggested human civilization was brushing up against a wide array of potential tipping points. 

There was the Ditlevsens’ finding last year that the AMOC was both slowing down and beginning to wander more — both “early-warning signs” for a collapse that they estimated could come as soon as midcentury.

That was bolstered by February findings in Science that confirmed such tipping in the AMOC was a real possibility.

This was “bad news for the climate system and humanity,” the authors of that study noted, because up until recently scientists could hope that AMOC tipping was “only a theoretical concept” that would vanish once scientists took a global view of the climate system and all its circling feedback loops.

If the AMOC collapsed, the Science authors suggested, there would be “strong and rapid cooling of the European climate” of 3 degrees Celsius, or up to 5 degrees Fahrenheit per decade — a level that, echoing Ditlevsen, the scientists said “no realistic adaptation measures can deal with.”

Also in February, a study in Nature found that as much as half of the Amazon — a forest that dates back to the age of the terrestrial dinosaurs — could be the site of “compounding disturbances” by midcentury that could lead to the sudden transition from forest to savanna.

That’s a possibility one study author told Carbon Brief was “very scary.”

And a 2020 study in Nature found that at about 2 degrees Celsius of warming — the upper limit set in Paris— the Antarctic Ice Sheet would be “committed to long-term partial collapse.”

The danger to the ice sheet, and to these key systems in general, is what scientists call “hysteresis” — a dynamic that can be thought of as a door that only swings one way. Once collapse occurs, it will be impossible to reverse, even if temperatures are brought back down in the future.

How big is the risk of multisystem collapse?

Considerable research suggests that the systems examined in the Nature study are closely interwoven with one another, creating the risk of “climate domino effects,” as a 2021 study in Earth System Dynamics put it.

That risk is not clear cut: Interactions between the pillars cut both ways, and in some scenarios collapse in one could lead to greater stability for others, rather than a cascade of failure. 

For example, on the one hand, the frigid fresh water streaming down from a collapsing Greenland ice sheet might destabilize the AMOC; on the other, a similar collapse of the Antarctic ice sheet could stabilize it.

There is also some evidence suggesting that a faltering AMOC could help halt the “dieback” of the Amazon, though researchers emphasize that the salvation would be paid for with “devastating impacts globally.”

But these potential saving graces in scenarios of collapse underscore the consistent risk raised by the scientific literature in this field: Even experts don’t really know how close we are to destabilizing the systems we rely on.

These risks go beyond the four earth systems that Thursday’s study looked at. One 2022 Science study into the risk of failure of nine key Earth systems — which include the thawing of methane-dense permafrost and coral reef die-off — found that collapse was possible even at 1 Celsius of warming.

That is a level the planet has already surpassed, though the scientists noted that every fraction of a degree of heat brought the danger closer.

What are scientists proposing to stabilize the climate?

Scientists posit that the most important step for mitigating the risk of collapse is to slow global heating — which is effectively melting the diverse structures of the Earth’s atmosphere, cryosphere and biosphere toward a dangerously soupy sameness — or to blunt its effects. 

Some recent strategies they’ve proposed to do so verge on science fiction. 

Over the last several years, there has been a surge of interest in solar geoengineering, which pursues approaches like brightening clouds to reflect more of the sun’s light and heat back into space, away from an atmosphere that is ever more polluted with heat-trapping emissions from fossil fuels.

For example, the Environmental Defense Fund and the University of Chicago each recently stood up working groups on the technology.

Solar geoengineering is controversial, however. The Bulletin of the Atomic Scientists compared it to deliberately mirroring the heat-blocking impacts of volcanic eruptions or pollution from coal plants.

Recent research suggests that deflecting the sun’s light back into space would be, at best, a stopgap: A June study in Nature found that “marine cloud brightening” could cut the risk of dangerous summer temperatures by as much as 55 percent over the continental U.S. — but only over the short term.

By mid-century, the study found, the method would only slightly reduce, or even increase, “heat stress in the Western United States and across the world” — in part because of how the AMOC would respond to both ongoing planetary heating and the impacts of decreased sunlight.

Perhaps more controversial than solar geoengineering, according to Science Magazine, is the strategy discussed in a July white paper, also from the University of Chicago, in which a team of polar scientists called for research into massive dams, boreholes and barriers that could help slow the melting of the ice sheets.

Such measures could help block ice sheets from the heated ocean water that melts them or drain away the pools of meltwater that would otherwise lubricate their slide into a warming sea.

But they’re the subject of much contention among scientists. 

“I honestly feel like this is ultimately going to be a civil war in the community,” University of Michigan glaciologist Jeremy Bassis told Science. “I don’t see an awful lot of room for compromise.”

These proposals are controversial in part because of their expense, lack of proven outcomes and potential for unforeseen consequences — but also because many scientists see them as a distraction from the most obvious solution, which is drastically reducing the main force driving the heating: the burning of fossil fuels.

A 2022 study in Nature Climate Change, for example, found that only cutting emissions in half by 2030 could “minimize risks” of tipping points for the world’s ice sheets.

Echoing the upshot of most papers on the topic, the authors of Thursday’s study emphasized the need for rapid cuts in emissions.

They said to avoid the risk of tipping points, human society needed to “at least” zero out greenhouse gas emissions by the end of the century, a process that they emphasized had to begin now.

Rapid cuts in emissions by 2030 “are critical for planetary stability,” they wrote.

How are efforts to cut emissions faring?

They’re not moving fast enough.  

Last year saw record emissions from fossil fuels, according to scientists at the Global Carbon Budget, which tracks the amount of coal, oil and gas that can still be burned without pushing Earth beyond a greater than 50 percent chance of passing the critical 1.5 Celsius threshold.

As of 2024, that budget stands at 275 billion metric tons of carbon dioxide — an amount that human civilization is on track to burn through within the next seven years. 

There is some evidence that global fossil fuel emissions will peak this year, but even if they do, the decline is likely to be gradual and may be outweighed by other factors, such as deforestation — or an expansion in the production of such fuels.

A 2023 report by the Stockholm Environment Institute found that world government fossil fuel production plans, if met, would by 2030 produce more than twice the amount of fossil fuels necessary to keep planetary heating below 1.5 Celsius, and more than half again as much as would keep it below 2 Celsius.

Both those numbers potentially surpass the level at which tipping points begin to be a risk.