Governor of California Gavin Newsom has launched a series of attacks on the fossil fuel agenda of US President Donald Trump.
Mr Newsom hit out at Mr Trump for twice leaving the Paris climate agreement and "doubling down on stupid" through his support of major oil and gas companies.
The governor - seen as a potential US presidential candidate in 2028 - said that a Democratic administration would rejoin the Paris Agreement "without hesitation".
"It's a moral commitment, it's an economic imperative," Mr Newsom said.
He was speaking to reporters at the United Nations climate conference in the Brazilian city of Belém.
President Trump is not attending the event - known as COP30.
After returning to office in January, he withdrew the United States from the landmark Paris deal for a second time - the first was during his first term - and sneered at the idea of human-caused planetary warming, calling it a "con job".
It is "an abomination that he has twice, not once, pulled away from the accords," Mr Newsom said.
The governor's first appearance of the day came alongside Helder Barbalho, Governor of Para in Brazil, where he touted California's green credentials, noting that the state, the world's fourth-largest economy, is two-thirds powered by renewables.
Mr Newsom then held meetings and press events with officials from Germany's Baden-Wurttemberg state, Brazil's Minister for Indigenous Peoples Sônia Guajajara and Brazilian President of COP30, Ambassador André Corrêa do Lago.
Regional leaders have no part in official negotiations at the conference, which opened yesterday with urgent calls to stay the course on climate action.
New Mexico Governor Michelle Lujan Grisham, who also attended events today, acknowledged these constraints.
"Certainly our meetings with leaders at the UN and others was to demonstrate that we're interested in any possibility that does more about that direct negotiation and representation."
Her aim in coming, she added, was to show that "when the federal government leans in, we do more, and when they lean out, we do more. It's both".
But Christiana Figueres, an architect of the Paris agreement, said the summit was better off without members of President Trump's government showing up.
"I actually think it is a good thing," she said, suggesting that while the US may work behind the scenes with petrostates, including Saudi Arabia, it "cannot take the floor" and directly bully other nations.
Even without a seat at the table, US states and cities have concrete power.
Recent analysis by the University of Maryland found that if these governments ramp up their efforts - and a climate-friendly president is elected in 2028 - US emissions could fall by well over 50% by 2035, approaching the 61-66% reduction targeted by former presdient Joe Biden's administration.
"The president can't throw a switch and turn everything off - that's not how our system works," Nate Hultman, who led the report, said.
Mr Hultman previously worked for Democratic presidents.
He said the market-driven green shift remains a strong factor, including in US states with climate-hostile leadership, such as Texas, the country's renewable energy generation leader last year.
However, there are questions over how far state-level action can go without support from Washington.
President Trump's Republican Party recently passed a law bringing an early end to clean energy tax credits, seen as a potentially crippling blow to the renewable sector.
Beyond pushing for more drilling at home and declaring war on green energy, the administration recently torpedoed international efforts to impose a carbon tax on shipping by vowing reprisals against countries that backed the plan.
Mr Newsom urged nations to hold firm against further intimidation efforts, saying it was vital to remember "Trump is temporary" and that "you stand up to a bully".
Ethiopia set to host UN's COP32 summit - Africa Group
Ethiopia is set to host the UN's COP32 climate summit in 2027 after the Africa Group of Negotiators backed the move.
"The AGN has endorsed Ethiopia," the group's chair, Richard Muyungi, said.
The Brazilian presidency of COP30 confirmed the African countries' choice.
This informal decision still needs to be officially adopted by all nations during the conference, which concludes on 21 November, but this is expected to be a formality.
"We welcome the announcement of COP32 in Ethiopia and look forward to elevating Africa's climate priorities and leadership," said Rukiya Khamis, Africa senior organiser at the nonprofit organisation 350.org.
UN climate conferences are organised in rotation among five regional blocs, which must select the host country by consensus within their group. The process can lead to power struggles.
This year, Brazil was chosen as host on behalf of Latin American and Caribbean states.
Africa's turn is scheduled for 2027, and Ethiopia was selected over Nigeria as the preferred host country.
However, obstacles remain for COP31 next year: Australia wants to host it in Adelaide, but Turkey refuses to back down and abandon its bid for Antalya.
Both countries belong to the "Western Europe and Other States".
Negotiations are ongoing, as the decision must be made in Belém.
Otherwise, COP31 will be held by default at the UN Climate Change headquarters in Bonn, Germany.
Such a deadlock would be unprecedented in the history of such conferences.
