The world must defeat climate denialism and fight fake news, Brazil's President Luiz Inácio Lula da Silva has told the opening meeting of the UN climate talks.
In a rallying cry to COP30, President Lula again made thinly veiled references to President Donald Trump who branded climate change a con job in September.
The two weeks of talks kicked off on Monday in the lush Brazilian city of Belém on the edge of the Amazon rainforest.
They take place against a fraught political backdrop and the US has sent no senior officials.
On Monday thousands of delegates poured into the COP venue in a heavily air-conditioned former aerodrome, some coming from accommodation in shipping containers and cruise ships moored on the riverside.
Members of the Guajajara indigenous group, in traditional dress, performed a welcome song and dance for assembled diplomats.
Addressing the conference, President Lula said COP30 will be the COP of truth in an era of fake news and misrepresentation and rejection of scientific evidence.
Without naming President Trump, President Lula continued, they control the algorithms, sow hatred and spread fear.
It's time to inflict a new defeat on the deniers, he said.
Since President Trump took office in January, he has promised to invest heavily in fossil fuels, saying that this will secure greater economic prosperity for the US.
His administration has cancelled more than $13bn of funding for renewable energy and is taking steps to open up more areas of the US to oil and gas exploration.
That puts the country at odds with the majority of nations still committed to reducing greenhouse gas emissions and investing in green energy.
This backdrop has put the COP talks in a difficult position as nations aim to make progress on tackling climate change without the participation of the world's biggest economy.
Some delegates fear that the US could still decide to send officials to undermine the talks. Other environmental talks collapsed this year following US pressure, labelled bully-boy tactics by some participants.
Addressing officials in Belém, UN climate chief Simon Stiell initially struck an optimistic tone. He said significant progress had been made in the last decade to reduce emissions of planet-warming gases.
But then he took aim at squabbling between countries.
Not one single nation among you can afford this, as climate disasters rip double-digits off GDP, he said.
Brazil wants to use its presidency of the talks to secure progress on key promises made in previous years.
That includes moving away from the use of planet-warming fossil fuels, finance for developing countries on the frontline of climate change, and protecting nature.
President Lula's centrepiece is a fund called the Tropical Forest Forever Facility (TFFF) that Brazil hopes will raise $125bn to protect tropical forests globally.
Fund-raising got off to a slow start. Last week UK Prime Minister Keir Starmer said, at the last minute, that the UK would not contribute public money.
But on Monday, UK climate envoy Rachel Kyte told BBC News that the fund was a brilliant idea and that the UK will make the investment at some point.
After a fight, nations finally agreed a conference agenda on Monday.
It promises to consider the question of whether countries can still work towards keeping global temperature rise to 1.5C above pre-industrial levels.
Groups on the frontline of climate change, including coalition called Alliance of Small Island States (AOSIS) that mostly represents Caribbean and Pacific countries, had insisted the talks address the long-held goal.
In recent weeks even the UN has said it accepts that overshooting this temperature is inevitable.
Last week UN General Secretary General António Guterres told leaders in Belém that the failure to limit global temperature rise to 1.5C was a moral failure and deadly negligence.
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