The most severe climate change scenarios now appear less likely, but extremes are nonetheless poised to overwhelm societies, scientists say
In the not-so-distant past, scientists predicted that global temperatures would surge dramatically throughout this century, assuming that humans would rely heavily on fossil fuels for decades. But they are revising their forecasts as they track both signs of progress and unexpected hazards. Accelerating solar and wind energy adoption means global warming probably will not reach the extremes once feared, climate scientists say. At the same time, recent heat, storms and ecological disasters prove, they say, that climate change impacts could be more severe than predicted even with less warming.
Researchers are increasingly worried about the degree to which even less-than-extreme increases in global temperatures will intensify heat and storms, irreversibly destabilize natural systems and overwhelm even highly developed societies. Extremes considered virtually impossible not long ago are already occurring.
Scientists pointed to recent signs of societies’ fragility: drought contributing to the Arab Spring uprisings; California narrowly avoiding widespread blackouts amid record-high temperatures; heat waves killing tens of thousands of people each year, including in Europe, the planet’s most developed continent.
It’s an indication that — even with successful efforts to reduce emissions and limit global warming — these dramatic swings could devastate many stable societies sooner, and more often, than previously expected.
“We see already that extremes are bringing about catastrophe,” said Claudia Tebaldi, an earth scientist at the Pacific Northwest National Laboratory in Richland, Wash. “The question is: How are we going to possibly adapt and lower the risk by turning the dial of what we can control?”
And researchers are watching closely to see if the planet is approaching — or even passing — tipping points in climate change: thresholds of ice loss or deforestation that would be so consequential, they would make cascading harms unavoidable.
“People are already dying of climate change right now,” said Sonia Seneviratne, a professor at ETH Zurich’s Institute for Atmospheric and Climate Science in Switzerland. “We have started to see events at near-zero probability of happening without human-induced climate change.”
‘Good news’: Worst-case warming appears less dire
The latest forecasts suggest Earth’s ever-thickening blanket of greenhouse gases has it on a path to warm by more than 2 degrees Celsius by 2100 — a threshold scientists and policymakers have emphasized as one that would usher in catastrophic effects.
That is despite efforts to keep warming below 2 degrees Celsius through the global treaty known as the Paris agreement, signed at a U.N. climate change conference in 2015. An October report from the United Nationsfound that if countries uphold even their most aggressive pledges to reduce output of climate change-inducing greenhouse gases, the planet would warm 2.4 degrees Celsius (4.3 degrees Fahrenheit) by the end of the century.
But the latest projections of warming nevertheless show humanity has made progress at reining in some of its planet-warming emissions, scientists said.
One scenario laid out in a 2014 Intergovernmental Panel on Climate Change report andcalled “business as usual” — predicting global emissions and warming without any policy intervention and continued adoption of coal-fired power — had suggested global temperature would rise as much as 5 degrees Celsius of warming above preindustrial levels by the end of this century. The likelihood of such sustained and rapid warming now appears remote.
“I think that’s good news,” Tebaldi said.
Climate scientists credit the rapid adoption of renewable energy — solar and wind power accounted for 1.7 percent of global electricity generation in 2010, and 8.7 percent of it in 2020. The world is set to add as much renewable energy generation in the next five years as it did in the past two decades, the International Energy Agency predicted in a reportreleased this month.
If energy transformations continue and technologies such as carbon sequestration become viable, climate models suggest global warming could eventually reverse, bringing temperatures back down close to 1.5 degrees above preindustrial levels. At the same time, many nations are failing to take the actions they’ve pledged to make that happen.
Some scientists have argued the most extreme projections of warming have long failed to account for clean-energy advances, in particular declines in coal use. Zeke Hausfather, one of those critics, said many climate scientists now agree they need to reconsider their projections.
“If we succeed really well, we can limit warming to below 2 degrees. If we do poorly, we can end up closer to 3 degrees,” said Hausfather, climate research lead at payments company Stripe and co-author of a key IPCC report. “We don’t think we’re heading toward a 4-degree world, but we can’t rule it out if we get unlucky.”
Even at lower warming, billions face ‘a challenging environment to live in’
If moderating projections of global warming are good news, the bad news is what is already unfolding: Average global temperatures have risen more than 1.1 degrees Celsius, or 1.9 degrees Fahrenheit, since the dawn of industry and combustion engines.
And that level of warming is less than half what is likely by the end of the century.
Take, for example, a heat wave that descended on the Pacific Northwest in June 2021. Portland and Seattle hit record highs of 116 degrees and 108 degrees, respectively. British Columbia broke Canadian high-temperature records three days in a row, peaking at 121 degrees — more than 40 degrees hotter than normal for that time of year.
Scientists quickly determined the heat was so extreme, it could not have occurred without the influence of global warming. Further research found that, in a world with 2 degrees of warming above preindustrial temperatures, it may be a once-in-a-decade sort of event.
Elsewhere, communities are facing the near-likelihood of sustained extreme heat. Half a century ago, about 12 million people endured average annual global temperatures greater than 29 degrees Celsius, or 84 degrees Fahrenheit; that number could grow to 3.5 billion people by 2070, one study found in 2020. Climate scientist Timothy Lenton, one of the study’s co-authors, called that “absolutely shocking.”
“I cannot believe we’d cope well in a world where billions of people are exposed to these kinds of extremes,” said Lenton, director of the Global Systems Institute at the University of Exeter in Britain.
Then there are the precipitation extremes. Many scientists have pointed to drought, and resulting surges in food prices, as a factor in anti-government uprisings in Arab countries in the early 2010s and in a civil war in Syria that has been ongoing for 11 years. Research on flooding in Pakistan that killed 1,500 people and affected 33 million people, leaving millions homeless,suggested climate change intensified rainfall by 50 to 75 percent.
The events echo U.N. reports asserting that human influence on weather extremes is strengthening and that climate change is already causing “dangerous and widespread disruption” to ecosystems and communities.
Many climate scientists said society has largely discounted weather extremes because of a bias toward what is most likely, rather than the range of what is possible.
But now, it’s becoming hard to ignore the reality of just how sweltering extreme heat can be, said Karen McKinnon, an assistant professor at the University of California at Los Angeles.
“We’re just now experiencing what that looks like and what that feels like,” she said.
Risks of catastrophe remain
The consequences of weather extremes also depend on factors beyond meteorology. Some climate scientists stressed that societies’ ability to manage disasters — and, especially in the future, multiple disasters at once — will help determine the level of hazards they face.
“Countries are not only going to be affected suddenly by one event,” Seneviratne said. “The risk is actually much higher than you would expect if you look at any one of them in isolation.”
For example, communities’ resiliency will depend on the stability of insurance markets in disaster-weary places such as Florida, or, more crucially, on the security of food and housing in places such as Pakistan.
“We model the individual impact of hazards, but we don’t model the potential ripple impacts through society,” said Luke Kemp, a research associate at the Center for the Study of Existential Risk at the University of Cambridge in Britain.
There are also risks that scientists are vastly underestimating the effects that could come with any given level of global warming, which has increased at a pace without precedent in the past 100,000 years. So there is no historical guide to analyzing how ecosystems and societies might react to the changes induced by greenhouse gas emissions.
That could mean that, even at some best-case scenarios of warming global leaders are aiming for, effects on the planet would be devastating, Seneviratne said.
And Kemp said it’s also important not to assume the latest global warming forecasts will become reality, and to keep in mind that what seems remote remains possible.
Though there are signs of progress at limiting greenhouse gas emissions, he called it a mistake to put much stock in predictions of what geopolitical and energy systems will look like decades into the future, and what that will mean both for how much greenhouse gases will be emitted and whether societies will be equipped to endure the warming those emissions bring.
“This narrative of, ‘Don’t worry, we’re on track for 2 to 3 degrees’ [of warming], I think, is seriously overconfident,” Kemp said.
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