The biggest climate meeting of the year opened in Brazil on Monday aiming to bring countries together, amid a difficult global backdrop of backlash to climate policies in Europe and an absent United States.
Brazilian president Luiz Inacio Lula da Silva warned of those who "sow hatred, spread fear, and attack institutions, science, and universities".
"It is time to impose a new defeat on denialists," he told countries gathered for COP30 in the Amazonian city of Belem.
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It was a veiled attack on the likes of US President Donald Trump, who calls climate change a "hoax", and emboldened populist parties in Europe and the UK that are attacking climate policies and questioning science.
UN climate chief Simon Stiell told negotiators on Monday: "Your job is to fight this climate crisis together."
Outwardly, countries were unphased that the US president is skipping the talks on climate change - despite being the largest historical emitter.
After all, the other 194 countries are still signed up, Brazil pointed out yesterday.
But Mr Trump's shadow still hangs over the summit, and some diplomats who want more action on fossil fuels privately expressed nervousness that his team could still stand in the way.
Last month, he successfully sank a proposed shipping levy after threatening sanctions and visa restrictions on those who backed it.
Germany's environment state secretary Jochen Flasbarth was asked whether Mr Trump might try the same tactics at COP30.
"I don't think so. But we'll have to wait and see," he replied.
He said a broader conference like this was less likely to worry the US president than the shipping levy, which would have been legally binding.
Fossil fuels versus clean energy
COP30 host nation Brazil, itself a major oil producer, says it wants to use the summit to map out how to end dependence on oil, coal and gas.
Two years ago, at COP28 in Dubai, countries set a vague target to "transition away" from fossil fuels - but there's been little progress since.
As the US seeks to lock countries into using its oil and gas for longer, China is forging ahead, building most of the solar panels, wind turbines and electric vehicles of the future, while still chugging coal itself.
The president of this year's conference, Andre Correa do Lago, said: "Emerging countries are appearing in this COP with a different role. China is coming with solutions for everyone."
UN climate chief Mr Stiell also talked up China's renewable power push. "Clean energy is the trend of our time, President Xi of China said."
German minister Mr Flasbarth said he had been to China, which is currently the world's largest polluter, three times in the last few months.
Although China's leader Xi Jinping also stayed at home, officials sent in his place talked up climate policies.
But 19 US states still have net zero targets, and Democratic politicians are arriving in Belem this week to nail their colours to the climate mast.
California senator Josh Becker said in a briefing: "Donald Trump does not speak for all Americans."
He added: "Yes, I think he will try to influence the talks. But we're going to continue to move forward."
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'Symbol of devastation'
Unamay Gordon, principal director of climate change for the Jamaican government, said: "I know that the subnational governments from the US will be here on the ground as well, and accountability has to come at all levels."
Jamaica is still picking up the pieces from the deadly Hurricane Melissa that slammed into its coastlines two weeks ago, which was intensified by climate change.
Ms Gordon said the country has become "the world's symbol of climate devastation".
An alliance of island countries, including Jamaica, will use COP30 to try to force countries to respond to a recent warning that the world is due to warm by levels that could push their lands underwater.
The summit is also hoped to launch various initiatives to protect and fund indigenous peoples, who are finally being recognised and rewarded for being the best guardians of their land.
(c) Sky News 2025: COP30: Climate summit kicks off with plea to work together - despite Trump-shaped hole
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