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.
Introducing the talks, UN climate chief Simon Stiell initially struck an optimistic tone, highlighting advancements in reducing emissions over the past decade but warned against the squabbling among countries.
With Brazil leading the charge, the hope is to secure progress on key promises made in previous years, including the fund called the Tropical Forest Forever Facility (TFFF) aiming to raise $125bn to protect tropical forests globally, although fundraising efforts have faced challenges.
After significant discussions, nations finally agreed on a conference agenda, promising to consider addressing global temperature rise levels.
