This is happening. Donald Trump is going to be president of the United States.

And there’s no way around it: What he’s planning to do looks like a disaster for the planet (and the people on it). Specifically, all the fragile progress the world has made on global warming over the past eight years is now in real danger of being blown up.

Trump has been crystal clear about his environmental plans. Much of the media never wanted to bring it up, never wanted to ask about it in debates, never wanted to turn their addled attention away from Hillary Clinton’s email servers to discuss what a Trump presidency might mean for climate change. But the warning signs were there:

Trump called global warming a Chinese hoax. He couldn’t have been blunter about this. He also tapped Myron Ebell, an avowed climate denier, to head his EPA transition team.

Trump has said, straight up, he wants to scrap many of the major regulations that President Obama painstakingly put in place to reduce US carbon dioxide emissions, including the Clean Power Plan. If Trump wants to weaken or delay these rules through executive action, he can. Even more drastically, Republicans in Congress could try to pass a law forbidding the EPA from ever regulating CO2 again.

Trump has said he wants to scale back federal spending on clean energy, including R&D for wind, solar, nuclear power, and electric vehicles. This would require Congress, but it’s hardly impossible.

Finally, Trump has said he wants to pull the United States out of the Paris climate deal. There’s nothing stopping him here. Technically, the US can’t officially withdraw for four years, but for all practical purposes, the Trump administration could ignore it.

So what happens if Trump gets his way? More air pollution, more carbon emissions. Exactly how much more remains to be seen. There are, after all, plenty of other factors pushing down US emissions that Trump has no control over. Natural gas from fracking would continue to kill coal power. Wind and solar would continue to grow. But it’s nearly impossible to imagine emissions under Trump dropping at the sharp pace necessary to slow global warming. And emissions could even rise.

Even more important, though, is the potential impact of Trump’s moves on the rest of the world.

The world was making fragile progress on global warming. Trump could blow that up.

For the last eight years, the Obama administration has been using every regulatory lever at its disposal to push down US greenhouse gases — aiming for a 28 percent cut below 2005 levels by 2025. Obama has also been trying to coax countries like China to participate in a global climate deal, in which every country would voluntarily pledge to restrain its emissions and meet regularly at the UN to ratchet up ambitions over time.

That plan finally came to fruition last December, when the world agreed to a sweeping climate agreement in Paris. The Paris deal was always delicate, and the current pledges weren’t nearly enough to avoid dangerous global warming, defined as 2°C or more. But the deal was a start. And the hope was that by cooperating and exerting diplomatic pressure on each other, all countries would steadily ratchet up action over time.

This plan, which Clinton wanted to build upon, was far from a sure bet to succeed. But it was arguably the most plausible and promising accord yet proposed in the history of international climate talks.

Now it’s in peril. If Trump yanks the United States out of the Paris agreement, the deal won’t die, but momentum could wane. One can easily imagine India deciding it doesn’t need to push nearly as hard on clean energy if the world’s richest and most powerful country doesn’t care. At best, progress would slow. At worst, the entire arrangement could falter, and we set out on a path for 3°C warming or more.

These are decisions that will reverberate for thousands of years and affect hundreds of millions of people. We can’t easily undo the effects of all that extra carbon dioxide we keep putting into the air. Without drastic reductions in emissions (or possibly risky geoengineering), global temperatures will keep rising. The ice caps in Greenland and Antarctica will keep melting. Once that process gets underway, we can’t reverse it. The seas will rise. South Florida will eventually vanish beneath the oceans. Megadroughts will become more likely in the Southwest. For generations and generations.

This is the future of humanity at stake. We’re at risk of departing from the stable climatic conditions that sustained civilization for thousands of years and lurching into the unknown. The world’s poorest countries, in particular, are ill-equipped to handle this disruption.

So is there any hope things won’t actually be this bad?

Okay, now it’s time for a deep breath.

Even under Trump, there will still be reason for hope. Political change unfolds in unexpected ways, and not everything on Earth revolves around the machinations of the US federal government. So here are a few reasons to think the fight against climate change is not yet lost:

The Trump administration could find it more difficult to roll back Obama-era climate regulations than they expected — as their efforts to rewrite EPA rules get bogged down by the courts and environmental groups skilled at litigation. As George W. Bush found in the 2000s, it’s not always easy to scrap existing environmental protections.

States like California and New York are still pursuing their own ambitious climate policies, and it’s possible those efforts could prove so successful that other states decide to follow suit.

Likewise, wind power, solar power, and electric cars will keep getting cheaper — it’s possible they’ll acquire a self-sustaining momentum, even without support from the US government. Or maybe some other new low-carbon technologies will emerge to shake up climate politics. (Small modular reactors, anyone?)

Climate activists will continue to push for action at local levels — much as they did during the George W. Bush years, when the Sierra Club began blocking a major planned expansion of coal power. It’s possible that opposition to Trump will galvanize a new generation of climate activists who find creative ways to address global warming.

Other countries still have their own reasons for tackling climate change, even China and India (which, note, is choking on deadly levels of air pollution in Delhi right now). It’s possible that Trump’s recalcitrance on climate change could motivate the rest of the world to redouble their efforts at curtailing emissions without us.

Heck, it’s even possible that Trump and the GOP could have a change of heart and decide that global warming is a real issue that needs to be taken seriously. It’s possible that Republicans could balk at repealing all these pollution regulations, realizing that they’re actually quite popular. Stranger things have happened.

So lots of stuff is possible. Climate change will continue to be a defining issue for generations, long after Donald Trump is gone — and there’s never reason to give up. But the landscape looks very different than it did a few days ago. The prospect of staying below 2°C looks increasingly remote. Right now Trump has given every indication that he wants to gamble with the future of the only planet around that’s known to support life. And it’s an irresponsible bet.

Further reading

— The 6 most important parts of Donald Trump’s energy policy

— From my colleague Ezra Klein: It’s now on America’s institutions — and the Republican Party — to check Donald Trump

— Andy Revkin offers a somewhat more optimistic take on environmentalism under Trump here. I disagree with his assessment of global politics, but obviously I could be wrong! His take is worth reading.