In December 2015, negotiators struck a deal in the French capital that had eluded the world for more than two decades. The Paris Agreement became the first global pact with the United States and China the worlds two great carbon superpowers to recognize the threat emissions pose to life on Earth and pledge to stop the damage.

Then chaos broke out. Exactly a year later, the United States, the worlds biggest cumulative source of emissions, elected a fossil fuel diehard in Donald Trump who quickly made his country the only one to withdraw from the accord. Jair Bolsonaro forged a similar path upon his election in Brazil, steward of the worlds largest rainforest, ramping up deforestation at a clip that tilted the scales for the first time toward more carbon-spewing in the Amazon than its canopy of leaves could absorb. China, the worlds largest annual emitter, initially canceled coal plants in droves, only to resume construction after a few years.

The latest review of the most up-to-date and trusted research available by the U.N.s Intergovernmental Panel on Climate Change, the worlds premier climate science body, led the U.N. secretary-general to warn that we have reached code red for humanity as carbon, methane and other heat-trapping gases so thicken in the atmosphere that the changes to our planets ecosystems are on the brink of becoming irreversible.

And now the world will convene again, in Glasgow, Scotland, to confront this existential emergency.

The U.S. has rejoined the Paris Agreement and, with the potential passage of the Build Back Better legislation as soon as next week, could set the stage for a clean-energy spending blitz. But Americas powerful fossil fuel industry has successfully torpedoed even modest policies put forward to wean the country off gas and oil, and just last week, the conservative majority on the Supreme Court agreed to consider limiting the federal governments power to regulate greenhouse gases.

India, now No. 3 in global emissions, has made huge investments in renewable energy but has balked at demands to do more to eliminate pollution. China, meanwhile, has closed its purse to overseas coal projects, only to ramp up production at home amid a global energy crunch.

This was always set to be the most important climate summit since that fateful meeting in 2015. Anticipating the pact as a turning point in national energy policies, the Paris Agreement stipulated that, after five years, the negotiators would gather at the annual United Nations-run conference to reassess and strengthen the carbon-cutting targets. (In a sign of how interconnected and fragile the global system has become, the worst pandemic in over a century delayed the confab by a year.)