Every September, at Climate Week in New York, there’s a big scientific and diplomatic reckoning with the global state of play. This year, the mood is pretty confused.
To begin with, it was a brutal summer: wildfires tearing through neighborhoods and clouding cities with toxic smoke; heat waves killing tens of thousands across Europe; a glacial collapse and landslide in Nepal so huge it registered as a 5.2 magnitude earthquake, flattening thousands of homes and killing over 1,300 people. And now comes an absolutely staggering, off-the-charts “Godzilla” El Niño that is already a record for this time of year and forecast to become the strongest in modern history and push the planet into uncharted climate territory.
But compared to years past, when conferences like these sometimes commandeered the world’s attention for a moment, the climate alarm this year is a bit less loud. Politicians have mostly moved on, in the United States and around the world. Over the past year, you might have read that the clean energy transition has pulled the planet back from the brink, and that scientists are growing less concerned about the truly alarming climate futures that once inspired a global political awakening. Global warming is real, that story goes, but it is turning out to be less frightening than we were told.
There is some truth here. The world has made real climate progress over the past decade, projected future warming has fallen quite a bit, and a worst-case emissions scenario known as “RCP8.5” — in which coal use would roughly quintuple by 2100 — is being phased out as implausible.
But a new round of forecasts from the climate science community is pretty alarming. Scientists used to worry about the possibility of the earth warming by a global average of two degrees Celsius (3.6 degrees Fahrenheit). That is now almost a certainty on the path we are on today. Scarier futures loom at three degrees and four. Thanks to the rapid rollout of green energy, those futures appear a bit less likely.
But because we’re still burning an awful lot of fossil fuel — and because the climate itself may have some surprises in store — harrowing temperature increases remain unnervingly possible. It’s not just that by moving too slowly we’ve lost the opportunity to avoid disruptive climate change. The high-end warming sometimes described as a “worst-case scenario” remains very much on the table, too. The world is busy with crises, and some policy leaders have tried to downplay or ignore climate change. But this is not the time for complacency.
Ten years ago, in Paris, the world’s governments agreed to limit global warming to well below two degrees Celsius of warming, which would protect at least some of the world’s coral reefs, prevent a doubling of the global population living with extreme heat, avoid projected crop losses across much of the world and save low-lying island nations from disappearing. On current pathways, we are virtually certain to exceed two degrees of warming by the end of the century — with about a 50 percent chance of doing so in the next 25 years.
And it could get hotter still. In fact, it probably will. At three degrees higher, the world’s ice sheets would be committed to millenniums of retreat. The share of species on land facing a high risk of extinction could double.
How likely is this future? According to conventional modeling of today’s policies and pathways, the odds are about even by 2100 — and three in four by 2150. Those dates are a long way off, but this would mean packing millions of years of climate transformation into a single century.
There is also a voluminous scientific literature about an even more hair-raising level of temperature rise — between four and five degrees Celsius of warming this century. This is the true climate doomsday stuff, with most effects growing exponentially worse and damages compounding, likely arriving faster than farms, cities, coastlines and ecosystems can properly adapt. Recent models tell us that current policies give us about a 25 percent shot at exceeding four degrees by 2150.
Those odds look a bit better than they used to. But we shouldn’t overstate our scientific confidence about an experiment we get to run only once, in a climate system whose intricacies remain mysterious and in which all of us and all of our descendants are going to have to live.
Uncertainty is decidedly not our friend when it comes to climate change, though conventional climate forecasts tend to sound reassuringly precise. Hold today’s climate policies constant, for instance, and our best models tell us to expect a long emissions plateau producing about 2.9 degrees of warming by 2100. But that is just a central estimate. Perhaps we’d get lucky, and warming would hit only 2.2 degrees, which would still be very harmful. Or perhaps we’d get unlucky, in which case it might hit 3.9 degrees, which would be truly catastrophic.
The real risks — and the potential surprises in store — now dwell in a tangle of feedback loops: clouds and water vapor, the retreat of reflective snow and ice, wildfires that release carbon, and an ocean that soaks up less of it as the seas warm and turn more acidic. The result is a system that is quite hard to model with true precision even if we know exactly how much carbon we will be producing over the next century. As the climate scientist Wally Broecker memorably put it, “The climate system is an angry beast and we are poking it with sticks.” Poke it with one or two fewer sticks, and it’s still likely to get pretty angry. It might also get very angry. We actually don’t know for sure.
Among the unwieldy variables is the planet’s rate of heat accumulation. Globally, warming has accelerated over the past 15 years, though the speedup is mostly as scientists expected given the decline of air pollution, which tends to cool the planet. But the earth’s energy imbalance measures how much sunlight is being absorbed by the planet, and how much heat is sent back out. The imbalance is the closest thing the planet has to a straightforward thermostat. It has roughly doubled in the past two decades. And scientists did not expect that.
There have also been worrisome signals from certain feedback loops. The earth’s ability to reflect heat back into space is declining, in large part because cloud cover is. Concentrations of some greenhouse gases have grown faster than predicted, which may be a sign that they are being released by natural processes we haven’t well captured in our models. One recent paper suggested that, for any given level of emissions, we should expect about 25 percent more warming — enough to bring a three-degree forecast above 3.5 degrees and a four-degree forecast to five degrees.
And these are all just questions about how the climate system might respond to all the ways we’ve already provoked it. Emissions, of course, are not fixed in stone but determined by human action. It may seem unlikely that humans will become less motivated to reduce climate change in the years to come. But anyone who believes policy can move only forward has not been watching American politics in recent years. Of course, better futures are possible, too, and the faster we can replace fossil fuels with clean energy alternatives and cut emissions, the more we reduce the risks of truly catastrophic warming.
In the meantime, don’t be fooled: Those risks are far too high and growing still with each molecule of carbon. The world still isn’t nearly concerned enough.
David Wallace-Wells (@dwallacewells), a writer for Opinion and a columnist for The New York Times Magazine, is the author of “The Uninhabitable Earth.” Zeke Hausfather is the climate research lead at Stripe and a research scientist with Berkeley Earth.
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