Thousands of climate experts, investors, campaigners and policy makers gathered in New York for Climate Week, which runs annually alongside the UN’s General Assembly meeting.

But this year’s gathering started with an unusual twist, after US President Donald Trump unleashed a tirade against climate change science, calling it the “biggest con job ever perpetrated on the world”.

Global warming was a hoax, European leaders were crippling their nations with climate policies made up by people with “evil intentions”, and radicalised environmentalists wanted to “kill all the cows,” he told delegates. There were audible gasps in the hall.

But as excoriating as it was, the American president’s speech did not appear to dampen the spirits of Climate Week-goers.

In fact, once they had picked their jaws up off the floor, delegates proceeded to press ahead with the task at hand.

Ahead of time, there had been concern that the new US administration’s climate denial policies would overshadow much of the discussion and the events, said Katharine Hayhoe, climate expert at Texas Tech University, who spoke at the opening of the UN Climate Summit on Wednesday.

“Not only has there been rhetoric and tangible actions from the US government to slow or even stop everything from research to communicating climate information to developing clean energy,” she told RTÉ News, “but many organisations that were previously more vocal on their own participation in climate action had gone quiet too”.

But as the week went on, she said: “I actually saw no loss in energy, no loss in enthusiasm, and I saw an increase in determination.”

Minister for Climate, Energy and Environment Darragh O’Brien, who was representing Ireland at UN Climate Week, agreed.

“If anything, it has reinforced the belief that we need to do better and that we need to work more closely together,” he said.

“Those of us, who believe in science, understand that we have a major issue here, and that we need to accelerate the measures that we’re taking to combat climate change and to continue to decarbonise.”

But while there was determination, Mr O’Brien acknowledged the US position could stoke opposition to climate policies elsewhere, especially as the cost of living rises.

Even though 40% of Ireland’s electricity last year was generated through renewables, up from 7% 20 years ago he said, people do not feel the benefits of more renewables coming onto the system.

“Climate and energy are more interlinked now than they’ve ever been.”

“Pressure on cost to households and normal working families and middle-income earners in particular in relation to energy is a risk, frankly, because it is turning people away,” he said.

“They’re looking at this and saying … is this because of climate change measures?

“It’s a battle for the truth and we’ve got to do a better job … to actually bring it back down to the citizens,” he added.

But while delegates at the Climate Summit weren’t swayed by Mr Trump’s climate denialism, there was a distinct shift in the conversation this year, observers said – away from decarbonisation and towards energy security.

That’s in no small part because of the rise of global tensions that have exposed the vulnerability of energy supplies.

Europe’s reliance on Russian oil and gas when Russia rolled tanks across the Ukrainian border in February 2022, was a case in point.

“Climate and energy are more interlinked now than they’ve ever been,” said Mr O’Brien.

Under Mr Trump, America has gone all in on national energy security but has axed Biden-era green energy incentives.

Addressing the General Assembly, he called renewables “a joke” and “too expensive”.

“I’ve always said I’m for affordable, reliable, secure energy that betters human lives.”

His Energy Secretary Chris Wright doubled down on that message as he did the rounds in New York.

The former fracking executive defended the administration’s scrapping of incentives for clean energy projects while pushing oil and gas production.

“I’ve always said I’m for affordable, reliable, secure energy that betters human lives,” he told a New York Times climate forum, “so if you do things to your energy system that make it more expensive and less reliable, I’m not for that”.

The United States was looking to “re-industrialise our nation”, Mr Wright said, and it needs cheap, available energy to do so.

Read more: Packed hall as Trump goes off script on world’s biggest stage

In his UN address, President Trump really had it in for wind turbines, calling them “so pathetic and so bad”.

He claimed China built all the windmills but barely used them at home – which isn’t actually true.

China is indeed the biggest emitter of greenhouse gases, largely from coal plants.

But in recent years, China’s domestic wind and solar power capacity has surged with renewables now accounting for nearly 23% of China’s total electricity consumption – surpassing oil and gas capacity for the first time this year.

Now as America relinquishes its climate leadership, China is stepping into the breach.

China’s leader Xi Jinping put in a surprise appearance at the UN Climate Summit and had a very different message to his American counterpart.

Appearing via videolink, Mr Xi said renewable capacity will reach 30% in the next decade and for the first time pledged to cut China’s greenhouse gas emissions by 7% to 10% by 2035.

Not enough, environmentalists said, but better than nothing.

In what appeared to be a thinly veiled rebuke of Mr Trump, who immediately pulled the US out of the international agreement on carbon emission caps on his return to office, the Chinese president said the green and low carbon transition was the “trend of our time”.

“While some country is acting against it, the international community should stay focused on the right direction,” he said.

It certainly sounded like a pitch to seize the global lead on climate.

The US, meanwhile, didn’t even have a representative in the room.

The European Commission President Ursula von der Leyen was also keen to burnish Europe’s credentials.

“The world can count on Europe’s climate leadership,” she told the UN meeting.

But as America diverges from the rest of the world on climate, experts said there’s a new challenge coming down the line – a massive upsurge in global energy demand to power AI data centres.

US data centres could double their use of electricity by 2030.

Experts call this the “load growth”.

The Trump administration’s solution is to keep coal plants burning to meet that demand.

Speaking at a Reuters event, Mr Wright said he expected the majority of US coal capacity, that had been due to be phased out, will stay online.

Europe, by contrast, wants to boost its green energy capacity – although the EU has committed to buying €750 billion worth of American oil, gas and nuclear products over the next three years.

If New York Climate Week is a dry run for the annual COP Summit, which will take place in Brazil in November, we can expect energy security and AI to top the agenda there too.

The United States, though, will not be participating.