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Imagine in the coming years a global politics shaped by resurgent nationalism. Governments prioritize their own energy and food needs, invest more in national security than in global development, and undercut international efforts to curb the emissions of greenhouse gases. In this future, carbon emissions will roughly double by the end of the century, hastening along with them the drastic array of catastrophic environmental effects linked to global warming, from the melting of the Arctic to heat waves that make whole regions uninhabitable to an intensification of the extreme droughts, wildfires and floods that have already blighted parts of the world this summer.

When some climate scientists speak casually, they categorize this imagined future as “Trump world,” a reference to former president Donald Trump’s rejection of climate science in favor of an aggressive nationalism that championed short-term economic growth no matter the looming calamities posed by a human-influenced climate change. But things don’t have to go that way.

That’s the underlying and somewhat hopeful message buried within the assessment report released Monday by the United Nations-convened Intergovernmental Panel on Climate Change. The report, the first of its kind since 2013, was compiled by 234 authors who drew on more than 14,000 scientific studies and carries the imprimatur of virtually every government in the world.

To be sure, its findings are bleak and shouldn’t be particularly surprising for anyone paying attention to the research published in the intervening years, including by the IPCC: The planet is warming at a rate not seen in 2,000 years; atmospheric levels of carbon dioxide are at their highest in 2 million years; the shift in the climate is leading to increasingly erratic and extreme weather events; and human activity is without a doubt responsible for (almost) all of it. It delivers “a code red for humanity,” said U.N. Secretary General António Guterres, who has spent much of his tenure in Turtle Bay urging greater political action in the face of global warming. “This report must sound a death knell for coal and fossil fuels, before they destroy our planet,” he added.

Whether that dramatic — and, as the scientific community insists, necessary — transition comes to pass is another matter. On some fronts, humanity is already too late. Limiting warming to an increase of 1.5 degrees Celsius (2.8 degrees Fahrenheit) above preindustrial levels looks to be a lost cause, with some models projecting the planet could reach that stage as early as the next decade. Temperatures are bound to get hotter in coming decades, the result, in part, of the failures of governments to heed years of warnings from climate scientists.

If warming increases beyond an average of 2 degrees Celsius — a trajectory that is possible absent significant curbs in global emissions — humanity veers into further uncharted territory. It would see the inexorable collapse of the Greenland ice sheet and a sea-level rise of more than six feet. That would inundate coastal communities and lead to a cascade of other societal and environmental effects, from surges in climate refugees to the vanishing of coral reefs.

Using a complicated modeling system, the IPCC laid out five socio-economic “pathways” for the decades ahead. “Trump world” — known in the IPCC’s taxonomy as SSP3 — is one of these pathways. If governments opt for a narrow-minded nationalism and collective initiatives like the Paris climate agreement fail, temperatures could rise by 3.6 degrees Celsius by the end of the century.

That looks like an increasingly unlikely scenario. Trump is out of office, and other hard-bitten nationalists on the world stage — especially Brazilian President Jair Bolsonaro — are seen more as climate pariahs than as heralds of a broader global trend.

But humanity is not close either to the IPCC’s most optimistic scenario, which calls for global carbon emissions to be cut to “net zero” around the midway point of this century. Attention is shifting to a November summit in Glasgow, Scotland, where world leaders are facing mounting pressure to act. “It’s more serious than it’s ever been, at a time that it seems as if some key nations are just unwilling to do their part, to bite the bullet and step up,” John F. Kerry, the Biden administration’s chief climate official, said last week. “I view this as the last, best hope for the world to get serious.”

Critics, though, contend that the Biden administration is not serious enough. Since taking office, it has issued more than 2,000 approvals for companies to drill for oil and gas on public lands, while still couching its climate agenda in terms friendly to fossil fuel companies. Democrats have to deal with a Trump-dominated Republican Party that is an outlier among mainstream Western right-wing factions on climate. Republican lawmakers, even some who are more willing to confront climate change than Trump, are whittling away at Democratic efforts to pass legislation that could help transition the United States toward a greener future.

“These politicians don’t dispute that the climate is changing, but they are absolutely in denial about what curbing it would entail,” wrote Kate Aronoff of the New Republic. “The report has made clear that the climate in which this country became a superpower no longer exists. So why are politicians stuck on twentieth-century answers to the twenty-first century’s problems?”

In coming years, they may be presented with less of a choice. “It’s now become actually quite obvious to people what is happening, because we see it with our own eyes,” Corinne Le Quéré, a professor of climate science at the University of East Anglia and a contributor to the IPCC assessment, told my colleagues. “You don’t have to have a PhD. You don’t need to be a climate scientist. You just need to be a person who looks out the window.”

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