Apparently I should be glad of the cool spell Phoenix is enjoying this weekend.

We are forecast to hit a mere 40C, actually only a tad below the average high temperature for the time of year. A few weeks ago it touched 49 degrees in the shade. Nature’s oven.

It was so hot some flights out of Sky Harbor, the city’s airport, had to be cancelled. Simplistically put, that kind of heat made the air too thin for aircraft to attain the lift needed for take-off. Other variables are involved, like altitude, runway length and the kinds of planes in question, but on one day in late June the complex equations for safe flying got too dodgy for normal operations.

This had happened once before, in 1990 when temperatures rose even slightly higher. Even so, the trouble at the airport attracted national headlines, not least because of something else that had happened weeks before: Donald Trump’s decision to pull the United States out of the Paris Accord on climate change. To his critics it was just one more vivid and simmering example of why, when it comes to warming, burying your head in the desert sand just isn’t an option.

The rest of the world could be forgiven for concluding that America, under President Trump, is nonetheless doing precisely that. You know, climate change is a hoax and even if it is real the sacrifices asked for in the Paris agreements weren’t fair on Uncle Sam. It’s America First baby, so feel free to wreck your economies, if this issue is so important to you. We’ll be fine.

Happily, though, that would be wrong. That Trump has done this thing is unforgivable, of course. But the federal government is not the only game in town when it comes to climate change. States and cities can take their own measures whether Washington likes it or not and many are doing so. Arguably, in fact, Trump’s F-U to the world has had a galvanising effect.

Take Phoenix. A Democrat-led city in an otherwise mostly Republican state – and the fifth largest in the US – it is not turning a blind eye to its special predicament as a natural cauldron. Last year a study by Climate Central and the Weather Channel found that the average temperature here had increased 1.12F over just a half century. No other big US metropolis saw such a large jump. In the days after Trump’s announcement, Mayor Greg Stanton said the city would take its own measures to adhere to the emissions-reduction targets set by the Paris Accord.

“If the president is going to abdicate leadership on this issue,” he declared, “mayors like myself and throughout the country, we’re going to step in and fill the void. Here in Arizona, extreme heat as a result of climate change is a huge issue.” Residents here may want to take particular note after monsoon rains caused the deaths of nine people, all members of one extended family from Phoenix, in a flash flood at a popular swimming hole north of the city last weekend. Phoenix has vowed to reduce its greenhouse gas emissions by 40 per cent by 2030 from 2005 levels.

As Mayor Stanton indicated, he is not alone in snubbing Trump and hitching his city to the Paris standards. Over 200 mayors have now joined the National Climate Action Agenda also committing them to the Paris process. “As 211 mayors representing 54 million Americans, we will adopt, honor, and uphold the commitments to the goals enshrined in the Paris Agreement,” they said in a statement. Among them was Eric Garcetti of Los Angeles who has pledged to lower the city’s average temperature by 3F over three decades. That includes doing things like developing “cool roofs” for buildings (not black) and planting more trees.

Governor Jerry Brown fought for and won an extension of the California cap and trade programme (Getty)

States are at it too. Thirteen have formed the US Climate Alliance that similarly commits them to Paris. But none have gone as far as California which last week, after arm-twisting by Governor Jerry Brown, passed a law extending the state’s current five-year cap-and-trade programme, that forces polluters to buy permits if they exceed strict emission standards, until 2030. It’s an ambitious initiative which should slash emissions. Meanwhile funds raised by cap-and-trade are earmarked for the completion of a high-speed train between San Fransisco and Los Angeles.

And it’s politically brave. The official cost to the state’s economy is put between $13bn and $22.5bn a year, but that might be optimistic. More than that, in order to get the two-thirds majority that Brown needed to immunise the cap-and-trade law from legal challenges, he had to convince at least eight Republicans to vote with the Democrats. And he managed, partly with the power of his rhetoric on the the threat that global warming represents. “A lot of you people are going to be alive, and you’re going to be alive in a horrible situation,” Brown, who is 79, told a hearing before the vote. “This isn’t for me, I’m going to be dead. This is for you, and it’s real!”

So, yes, it’s true, the Golden State produces only 7 per cent of America’s emissions – and a mere 1 per cent of them globally. And there are flaws in the California model, including the likelihood some of its worst polluters will just up-sticks to another state with fewer regulations.