On Monday night, the Mendocino Complex wildfire became the biggest in California history — and, having burned through 283,000 acres, was just 30 percent contained. “Complex” is because the fire started as two distinct blazes, the “Ranch” and “River” fires, later married in one hellish flame. “It is extremely fast, extremely aggressive, extremely dangerous,” Scott McLean of Cal Fire told the Los Angeles Times. “Look how big it got, just in a matter of days … Look how fast this Mendocino Complex went up in ranking. That doesn’t happen. That just doesn’t happen.”
The Mendocino Complex is only one of a dozen wildfires roiling California right now. But the second record-breaking wildfire season in California within the last 12 months was hardly the day’s worst climate news.
In an alarming report published in the prestigious Proceedings of the National Academy of Sciences, 16 scientists warned that — thanks to a series of dramatic positive-feedback loops they suggest might be significantly underestimated by the U.N.’s Intergovernmental Panel on Climate Change, which effectively establishes the boundaries of acceptable discourse on global warming — the planet may already be heading down a far more harrowing warming path than most scientists, and certainly most nonscientists, understand.
In particular, the team of 16 scientists suggested that, while the Paris climate accords committed the world to the goal of stabilizing global warming below two degrees Celsius, in fact there may not be a natural planetary equilibrium there — and so even if we managed to hit the emissions targets consistent with only two degrees of warming, a series of accelerating climate-system feedback loops would be triggered anyway, bringing us quickly past three and even four degrees Celsius. They called this possibility the “Hothouse Earth” pathway, and they outlined an even darker, worst-case scenario in which feedback loops brought us up to six or even seven degrees.
How bad would this be? At four degrees of warming, according to some estimates, nearly all of Africa and Australia, most of the United States, South America north of Patagonia and Asia south of Siberia would be rendered uninhabitable by combinations of desertification and flooding. At six degrees, we would see relatively rapid sea-level rise of up to 200 feet. At seven degrees, much of the planet’s equatorial band would be so hot that humans could not move around outside without quickly dying. And, keep in mind: while the Paris accords articulated a goal of two degrees, the emissions commitments contained within it were far from sufficient to meet that goal; most previous estimates, which do not account for any dramatic feedback loops, suggest those commitments would only get us to 3.2 or 3.4 degrees. And no major industrialized nation is on track to meet even those commitments.
The feedback loops outlined in the PNAS article are not news, per se, and will be familiar to readers who have ever scanned the internet’s climate-doomsday fringes: melting arctic permafrost releases large amounts of frozen methane, more than 30 times more powerful a greenhouse gas than carbon dioxide; rapid disappearance of arctic sea ice means much less sunlight is reflected back by the planet and much more of it absorbed; a collection of climate conditions transform the Amazon rain forest from a “carbon sink,” which eats carbon dioxide and produces oxygen, into an additional carbon producer. All three of these effects, it is worth pointing out, are already under way — the Amazon is today absorbing a third less carbon than it did just a decade ago, for instance. The open question concerning scientists is whether these effects will accelerate, and, if so, just how quickly.
The authors of the new paper do not suggest a “hothouse earth” is an inevitability — only that it is significantly more likely than most scientists would publicly acknowledge. A similar argument is often made casually by climate scientists, many of whom regard the IPCC as overly cautious and mindful of political realities even in its cold-seeming description of the state of the science (barely mentioning feedback loops in its reports, for instance). More dramatic versions of this charge are contained in Deep Adaptation, a new work of holistic climate alarm by Jem Bendell of the U.K.’s University of Cumbria, and in a terrifying update to Australia’s National Center for Climate Restoration 2017 “What Lies Beneath” report, scheduled for release later this month.
These sorts of warnings are published with some frequency on the fringe. But the scientists behind the PNAS paper are probably the most distinguished yet to be raising this particular alarm — that the scientific community has dramatically understated the existential risk posed by climate change, and that the scientists who had previously been disregarded as alarmists may be, in fact, the more reliable guides to our near future. “These tipping elements can potentially act like a row of dominoes,” Johan Rockström, executive director of the Stockholm Resilience Centre and one of the authors of the paper, told the Independent. “Once one is pushed over, it pushes Earth towards another. It may be very difficult or impossible to stop the whole row of dominoes from tumbling over.”
The authors of the new paper also worry that the unprecedented months of climate disaster we’ve seen this summer may not be an outlier or just bad luck but a sign that the planet is already on its much more dramatic climate-change course. “The heatwave we now have in Europe is not something that was expected with just 1C of warming,” Rockström told the Guardian. (One degree is where the planet sits right now.) “Several positive feedback loops are already in operation, but they are still weak,” he continued. “We need studies to show when they might cause a runaway effect.”
“Runaway” is a terrifying term for those who work in climate change, and not one that gets tossed around very casually. It is typically used to refer to the kind of rapid climate devastation scientists believe once hit Venus — transforming what was once an ocean-rich planet, theoretically capable of supporting life, by literally boiling its water into the atmosphere, leaving an entirely inhospitable desert planet behind. Rockström and his colleagues are not predicting that, for Earth, but is very telling that they are using the word at all — it suggests they think we should at least be worrying about the possibility. By which I mean: doing much, much more to halt warming in its tracks.