The 1.5-Degree Paris Goal Is Effectively Dead. Leaders at COP31 Face the Question of What Comes Next

At COP31 in Antalya, Turkey, the diplomats who spent a decade chanting "Keep 1.5 Alive" are now saying out loud that it can't be done. Chris Bowen, Australia's minister for climate change and energy, who is leading the negotiations, put it without cushioning: the world has no chance of holding to 1.5 degrees.

The slogan referred to the central ambition of the 2015 Paris climate agreement, in which almost every country pledged to try to limit global warming to 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, above preindustrial levels. Eleven years on, scientists say that without drastic cuts in greenhouse gases, the planet will very likely warm at least 2.6 degrees Celsius, or 4.7 degrees Fahrenheit, by the end of the century.

Scientists have long warned what the extra warming means: more frequent and intense extreme heat, more powerful and destructive storms, rising seas, and the heaviest damage falling on poor countries. In recent months, that picture has been arriving in real time. Wildfires have burned from Canada to Indonesia. A glacier collapse in Nepal killed thousands and wiped away towns. Floods and mudslides devastated Brazil. A European heat wave killed an estimated 50,000 people.

With 1.5 slipping away, the open question in Antalya was what goal, if any, should take its place. Many leaders answered: none. Ilana Seid, Palau's ambassador to the United Nations, said she doesn't think there is a new target; the Paris target of 1.5 still stands, and her delegation will keep saying so. Rachel Cleetus, who directs the climate program at the Union of Concerned Scientists, argued the debate over a replacement number misses the point. There is no new number, she said. The world is now in the unsafe zone.

Leaders also turned down the idea of resetting the goal to 2 degrees or even 2.5. Their worry was that endless revisions create a slippery slope that would make progress harder to achieve.

At the same time, they said that having missed the target does not mean the target is gone for good. It might still be possible to get back to 1.5. António Guterres, the United Nations secretary general, urged countries to redouble emission cuts to limit further warming and eventually turn down the Earth's thermostat. We have the power, he said, to determine how high, how long and how devastating the overshoot will be, and to make it a temporary breach rather than a permanent sentence.

Making the breach temporary would require humans to find a way to lower greenhouse gas concentrations in the atmosphere, and that will not be easy. Emissions remain near record levels. A path back to 1.5 would demand a drastic reduction in burning coal, oil and gas, yet the world is expected to keep using fossil fuels for decades even as clean energy grows rapidly.

Because cutting emissions is proving so hard, some environmentalists and scientists are proposing geoengineering: large-scale carbon capture and storage, or injecting particulate matter into the stratosphere to reflect the sun's energy away from the planet.

Hilda Heine, president of the Marshall Islands, a nation threatened by sea level rise, framed the stakes for those on the front line. Overshoot, she said, must be kept as small and short as possible and rapidly reversed. The emissions reductions needed to stay under 1.5 were not achieved, and she said the world must rewrite the future. What to watch now is whether emissions fall fast enough to bring temperatures back down, and whether geoengineering gains ground as a stopgap.