The COP30 climate summit opened on Monday with the UN climate chief urging countries to cooperate rather than battle over priorities, as efforts to limit global warming are threatened by a fracturing international consensus.

Host country Brazil brokered a deal on the agenda for the two-week summit in the Amazon city of Belem, deflecting attempts by developing-country negotiating blocs to shoehorn contentious issues like climate finance and carbon taxes into the talks.

It was unclear whether countries would aim to negotiate a final agreement for the end of the event – a hard sell in a year of fractious global politics and US efforts to obstruct a transition away from fossil fuels.

Some including Brazil have suggested that countries focus on smaller efforts that do not need consensus, such as deforestation, after years of COP summits making lofty promises only to leave many unfulfilled.

"In this arena of COP30, your job here is not to fight one another – your job here is to fight this climate crisis, together,” UN Climate Change Executive Secretary Simon Stiell told delegates from more than 190 countries attending.

He said three decades of UN climate talks had helped to bend the curve in projected warming downward, “because of what was agreed in halls like this, with governments legislating, and markets responding. But I am not sugar-coating it. We have so much more work to do."

A new UN analysis of countries' emissions-cutting plans estimated that global greenhouse gases would decrease 12 percent by 2035 from 2019 levels, improving on an earlier estimate of 10 percent published last month.

The new figure takes into account the most recent pledges, including from China and the EU, but was still short of the 60 percent emissions drop needed by 2035 to limit global warming at 1.5 degrees Celsius above pre-industrial temperatures – the threshold beyond which scientists say climate change would unleash far more severe impacts.

Brazilian President Luiz Inacio Lula da Silva warned against interests trying to obscure the dangers of climate change.

"They attack the institutions, the science, the universities," he said. "It’s time to impose another defeat to denialists.”

The world’s biggest historical emitter of greenhouse gases – the United States – opted to skip the summit; US President Donald Trump falsely asserts that climate change is a hoax.

California Governor Gavin Newsom and New Mexico Governor Michelle Lujan Grisham were expected in Belem on Tuesday.

"What the hell is going on here?” Newsom said of the US government’s absence from the talks, addressing a global investors summit held on Monday in Sao Paulo.

“We're in Brazil, one of our great trading partners, one of the world's great democracies. I mean, hell, home to all the rare earth metals we need. This is the country we should be engaging with instead of giving the middle finger with 50 percent tariffs,” Newsom said, referring to duties imposed by the Trump administration.

COP30 President Andre Correa do Lago told a news conference: "I think that the absence of the US... has opened some space for the world to see what developing countries are doing." (Reuters)