We live in times of extraordinary and abrupt change, not just in the climate.
On January 17, US President Barack Obama gave $500 million to the UN's Green Climate Fund, part of the architecture of the Paris accord designed to help the poorest and hardest hit areas. Three days later he was replaced by Donald Trump, who had declared in a stunt tweet that global warming was a Chinese hoax. There was, and remains, no evidence Trump had spent even five minutes considering the science he rejected.
Trump's recent confirmation that he will act on his pledge to pull the US out of the global climate deal – a pledge that, like most people, he almost certainly never believed he would have the chance to act on – is likely to have unpredictable consequences. But there will be a couple of obvious upshots.
There will be calls from hard-right politicians and media cheerleaders to follow his retreat, either through complete withdrawal or a weakened response. They may have some success, here and there.
Secondly, as the US is responsible for nearly a fifth of global carbon dioxide emissions, Trump's reversal of Obama's clean energy plan will have a real-world impact that increases warming, and changes the planet in ways that affect lives and challenge species' ability to survive. Part of it will be offset by what's happening at state level - California, bigger than most countries, is cutting emissions by 40 per cent by 2030 - but it will do damage.
This was happening even if he stayed in the accord. To some extent, the Paris deal was a global show of good faith. There is nothing in it forcing countries to meet their (to date, mostly inadequate) targets.
But here's the other side of the coin. Action is happening, direct or not, and regardless of Trump. Three-quarters of the 195 governments that signed the Paris accord moved quickly to explain it to their citizens and formally ratified it.
Talk to business leaders and you will hear that Paris has changed things. The accord was never going to be a solution on its own. For starters, its numbers don't add up to solving the problem. But investors recognised it put the world on an inevitable path to cutting emissions.
Politics alone suggests the Australian government will hold its line on the accord. Poll after poll has found a majority of Australians want action on climate change. After abolishing a functioning carbon price, the Coalition has spent years trying to rebuff the idea it isn't serious about the problem, including designing a $2.5 billion direct action policy to appear to be doing something. It's unlikely to suddenly tell the electorate it doesn't care by just walking away.
Adam Morton is on Facebook and Twitter