Until now, at least for those watching from afar, the Trump show has been a spectacle. It has shocked and appalled, but with the compulsive appeal of something like entertainment. The accelerating investigation of collusion between the Trump campaign and Russia has followed the story arc of a gripping political thriller, a real-life rival to House of Cards. Indeed, the latest episode of the Trump-Russia drama promises a cameo role for our own Nigel Farage, now named as a “person of interest” to the FBI’s inquiry (even if voters in seven UK parliamentary contests deemed him anything but).

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Meanwhile, Trump’s tweets have provided a daily source of jaw-dropping amusement for a global audience, a phenomenon that reached a peak with the kerfuffle over “covfefe”, the apparently mistyped word in an incomplete tweet that the president posted after midnight on Wednesday.

The meme artists got to work on that one, imagining covfefe might be Trump’s safe word, or else an incantation that could summon an ancient spirit wizard from the deep. Unable to admit that his boss had been guilty of a simple typo, spokesman Sean Spicer – who back in January had pretended a small crowd was bigger than a big crowd – declared that “The president and a small group of people know exactly what he meant”. Oh, how we laughed.

But then, in the White House rose garden yesterday, came the announcement – trailed by Trump as if it were a season finale of the Apprentice – that the US would pull out of the Paris agreement on climate change. And suddenly Trump wasn’t so funny any more.

The consequences seem obvious. An accord that took years to broker, painstakingly put together in 2015 after failure at Copenhagen in 2009: a deal that brought together the powerhouses of India and China as well as the old world polluters of Europe and sought, at one minute to midnight, to do something to save our precious planet – that deal will now have to proceed without the world’s biggest economy and dominant superpower. It is an act of the most wanton vandalism, taking a delicate structure assembled piece by piece by all humanity – and kicking it with a steel-toecapped boot. The environmentalist Bill McKibben put it succinctly: “It amounts to a thorough repudiation of two of the civilising forces on our planet: diplomacy and science.”

Why would anyone do such a thing? The evidence of climate change and its destructive effects are as visible in the US as anywhere: on current projections, Trump’s own Florida resort of Mar-a-Lago will be under water by 2060. It can’t be that the president felt bound by the campaign promises he had made: he breaks those casually, whether it’s a commitment to deprive no Americans of existing healthcare coverage, or a pledge to shift the US embassy in Israel from Tel Aviv to Jerusalem (an incendiary promise Trump thankfully reneged upon this week).

The speech announcing his decision gave it a philosophical patina, as Trump returned to the “America first” theme of his inaugural address, describing the world as a site of Hobbesian, dog-eat-dog competition in which global cooperation is for wimps and suckers.

Any deal that delighted humanity as much as the Paris accord had done – “They went wild, they were so happy,” Trump recalled with lip-curled distaste – could only mean the United States was getting screwed. Or as he put it, the world was glad, “for the simple reason that [the Paris accord] put our country, the United States of America, which we all love, at a very, very big economic disadvantage”.

Naturally, insider accounts suggest electoral calculation: Trump reckoned that the people who put him in the White House, especially blue collar workers in the rust-belt states, have long seen global warming as a con. And they’re the ones he needs to keep sweet in time for next year’s midterm elections, and his own bid for a second term in 2020.

I’d suggest that even that level of calculation gives Trump too much credit. Sure, he declared his love for coalminers, as if withdrawing from Paris is going to save their industry when US coal jobs have been declining for a century, and fewer Americans mine coal than work in Disney World. But this being Trump, you need to look for even baser motives.

Facebook Twitter Pinterest Emmanuel Macron ‘out-alphas Trump with a knuckle-crushing handshake’. Photograph: Evan Vucci/AP

A desire to upend one of his predecessor’s big achievements will be one of them. But just as likely, surely, is that Trump was irritated by his treatment during last week’s Nato and G7 summits, and wanted to hit back. The Europeans barely hid their disdain for him, and so he seized the chance to deprive them of something they cherished.

If we were discussing a normal president, it would be absurd to bring up such things, but Emmanuel Macron might have erred when he made public his deliberate attempt to out-alpha Trump with a knuckle-crushing handshake. Trump would think nothing of getting his own back by burning the entire planet. Witness the White House aide who confessed that European leaders’ “snarky comments” had not helped, while another said Trump saw the disappointment of European allies as a “secondary benefit” of breaking the accord.

Fewer Americans mine coal than work in Disney World

This, then, is the measure of the man in charge of the world’s most powerful nation. Consolation comes from the fact that others have stepped in to fill the void he has created. Inside the US, states and cities have said they will continue to honour their commitments, regardless of Trump’s tantrum. “I was elected to represent the citizens of Pittsburgh, not Paris,” Trump said, whereupon the mayor of Pittsburgh sided with his fellow mayors around the world and promised to abide by the agreement. Trump was perhaps unaware that in Pennsylvania renewable energy employs 65,000 – more than oil, gas and mining combined.

Globally, it was a similar story, with Angela Merkel and Macron (but not, take note, Theresa May) apparently vying for the title to which Trump has lost all claim: leader of the free world. “Make the planet great again,” said Macron in an English-language video rebuttal of Trump. More quietly, China has signalled its own readiness to take up the role vacated by the US and, starting with climate change, to act as the dominant global power.

That’s good for the planet, but not so great for the world. Of course, when it comes to climate change, some leadership is better than none; but the notion of an international order underpinned by China, a dictatorship, is hardly a cheering prospect.

Yet this is the future that Trump, who last week refused to reaffirm the Nato principle of collective self-defence, is inviting. The New York Times columnist David Brooks greeted the Paris decision with a declaration that Trump is making “our country seem disgusting in the eyes of the world”. That is strong, but not far off the truth. Until now the world has been riveted, even amused, by the Trump show. As of this moment, it is sickened.