It faces tough odds, with a hostile United States unlikely to show up, political appetite for climate action at a low ebb, and eye-watering prices for accommodation threatening turnout.

Some 50,000 attendees are expected at the two-week COP30 conference starting November 10 in Belem, a city in one of Brazil's poorer states best known as a gateway to the Amazon rainforest.

On Monday, climate ministers meet in Brasilia ahead of the marathon UN negotiations that bring together nearly every nation for the most important climate talks of the year.

Belem is a symbolic yet fraught setting and a personal choice of Brazil's President Luiz Inacio Lula da Silva, who wants to spotlight the rainforest's role in absorbing carbon dioxide.

But pressure is mounting on COP30 to provide more than just a scenic backdrop as the world approaches the 1.5C warming target agreed under the Paris climate accord a decade ago.

The last two years were the hottest ever recorded, and major polluters are not cutting emissions fast enough to avoid destructive and potentially irreversible changes to the planet.

Lula -- whose own environmental record is mixed, having slowed Amazon deforestation but approved new oil exploration -- has promised a "COP of truth".

"It will be the moment for world leaders to prove the seriousness of their commitment to the planet," Lula told the United Nations General Assembly on September 23.

A likely candidate for re-election next year, Lula is determined to burnish Brazil's global standing after hosting recent major summits of BRICS and G20 nations.

He has invited dozens of leaders to Belem ahead of the negotiations, but numbers are not yet confirmed.

Prince William will represent Britain's King Charles and the leaders of South Africa and Colombia are expected, but Austria's president has already declined, citing high hotel prices.

Officials in Gambia, Cape Verde and Japan also told AFP they expected to reduce the size of their delegations.

- Tense times -

US President Donald Trump, who declared climate change a "con job" during his own UN address last month, is not expected to attend, nor is anyone else from his administration.

The United States intends to withdraw from the Paris Agreement for a second time as it promotes fossil fuels at home and abroad.

Brazil is adamant that COP30 shows global climate solidarity is alive even as wars, tariffs and populist politics shake the international order.

The US absence has underscored the lack of an obvious climate leader in Belem, particularly as the European Union deals with internal revolt over its green agenda.

COP30 CEO Ana Toni told AFP in an interview in September that it was an "extremely difficult" time to be rallying for climate change.

"COPs are not isolated. They reflect the tensions of geopolitics," she said.

A more pressing problem has been the astronomical cost of accommodation in Belem with schools, cruise ships and even rent-by-the-hour motel rooms enlisted to offer cheaper options.

Lula flatly rejected calls to move COP30, even as delegates from the developing world -- countries Brazil claims to champion -- complained they could not afford to attend.

"I know the problems in Belem," Lula said during an October visit to the city of 1.4 million where more than half the population live in shanty towns.

"We accepted the challenge of organising COP here because we must show the world what the Amazon is."

Far from a presidential suite, the 79-year-old leader vowed to "sleep on a boat, in a hammock" during the event.

- Reckoning -

Forests will be a focus in Belem but "we shouldn't expect headlines or agreements on big, flashy issues" at COP30, Marta Torres-Gunfaus, from sustainable development think tank IDDRI, told AFP.

A showdown over faltering climate action seems unavoidable with India and the EU among dozens of countries months late in submitting their latest 2035 emissions reduction targets.

Many commitments have fallen short of expectations, including from top polluter China.

The Alliance of Small Island States "is very clear that COP30 must deliver a response to this", Ilana Seid, a diplomat from Palau and chair of the climate-vulnerable grouping, told reporters.

Some of the world's poorest countries also want to reopen a tortured debate over the level of finance they receive from the richer countries that are most responsible for the climate crisis.

COP30 must offer clear commitments to boost financial assistance, "not more empty promises", the Least Developed Countries bloc of underdeveloped nations said last month.

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