About 50 heads of state and government are expected in the rainforest city of Belem for a summit on Thursday and Friday ahead of the annual UN Conference of Parties (COP) climate negotiations that open next week.

Almost every nation is participating, but Washington is sending nobody, with President Donald Trump having branded climate science a "con job."

UK Prime Minister Keir Starmer and French President Emmanuel Macron are expected in Belem but other major economies, including China and India, are sending deputies or climate ministers.

The choice of Belem, a city of 1.4 million people, half of whom live in working-class neighbourhoods known as favelas, has been controversial due to its limited infrastructure, with sky-high hotel fees complicating the participation of small delegations and NGOs.

Authorities have invested in new buildings and renovations, but with fewer than 24 hours to go to the leaders' summit opening, media teams and delegation scouts arrived at the COP venue Wednesday to find building works still very much underway.

Nonetheless, Karol Farias, 34, a makeup artist who came to shop at the newly spruced up Ver-o-Peso market told AFP: "The COP is bringing Belem the recognition it deserves."

- Uphill battle -

Brazil is not seeking to land a big deal at COP30, but rather to send a clear signal in an uncertain time that nations still back the climate fight.

The US absence will linger awkwardly during the summit, as will Brazil's recent approval of oil drilling near the mouth of the Amazon River.

So, too, will the unanswered call for a wave of ambitious new climate pledges ahead of COP30, and the stark acknowledgement from UN chief Antonio Guterres that the target of limiting global warming to 1.5 degrees Celsius from pre-Industrial levels will be missed.

Host Brazil is also still scrambling to find affordable rooms in Belem for cash-strapped countries.

The COP30 presidency on Tuesday said it had secured outside funding to provide three free cabins aboard cruise ships for delegations from low-income countries.

Brazil has acknowledged the uphill battle it faces rallying climate action at a time of wars and tariff disputes, tight budgets, and a populist backlash against green policies.

In a sobering reminder of the task at hand, a closely watched vote last month to reduce pollution from global shipping was rejected under intense pressure from the United States.

Leaders gathered in Belem "need to deliver a clear mandate to the COP to be ambitious and to close the gap and to address the issues that are burning," Greenpeace Brazil executive director Carolina Pasquali told AFP from aboard the organization's Rainbow Warrior flagship, docked at the city's port.

- 'Enough talk' -

Rather than producing a slew of new commitments, Brazil has cast the summit as an opportunity for accountability.

"Enough talking, now we have to implement what we've already discussed," Brazil's President Luiz Inacio Lula da Silva said this week.

Brazil is putting diplomatic muscle into pitching a global fund that would reward tropical countries for protecting rainforests.

It has also put a particular emphasis on adaptation, a key demand of countries pushing for more help to build defenses against rising seas and climate disasters.

"This is not a charity, but a necessity," Evans Njewa, a Malawian diplomat and chair of the Least Developed Countries bloc, told AFP.

These countries want concrete detail on how climate finance can be substantially boosted to $1.3 trillion a year by 2035 -- the estimated need in the developing world.

The hosts are also under pressure to marshal a response to the collective failure to limit warming to 1.5C as agreed in the landmark Paris accord a decade ago.

Even if all commitments are enacted in full, global warming is still set to reach 2.5C by century's end.

"For many of our countries, we won't be able to adapt our way out of something that overshoots over two degrees," Ilana Seid, a diplomat from Palau and chair of the Alliance of Small Island States, told AFP in October.

They, among others, want to tackle fossil fuels and push for deeper cuts to greenhouse gas emissions.

Lula said Brazil wants to "propose a roadmap for reducing fossil fuels" but conceded it was a difficult conversation.

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