The stakes are high for the COP29 conference in Azerbaijan where nations must agree a new target to fund climate action across huge swathes of the world.

It comes in a year likely to be the hottest in human history that has already witnessed a barrage of devastating floods, heatwaves and storms in all corners of the globe.

Nations are falling far short of what is needed to keep warming from hitting even more dangerous highs in the future.

But leaders arriving in Baku are wrestling with a host of challenges, including conflicts in the Middle East and Ukraine, trade spats and economic uncertainty.

Adding to the uncertainty, the US vote and potential return of Donald Trump, who pulled out of the Paris Agreement and has called climate change a "hoax", could ripple through the negotiations and beyond.

"You can imagine that if Trump is elected, and if the election outcome is clear by the time that we get to Baku, then there will be sort of a crisis moment," said Li Shuo, a Washington-based expert on climate diplomacy at the Asia Society Policy Institute.

He said that countries, likely including China, are preparing to send a "clear message" in support of global climate cooperation if Trump beats his rival Kamala Harris to the White House.

Samoan diplomat Pa'olelei Luteru, chair of the Alliance of Small Island States, said regardless of who wins "multilateralism is imperative".

"Our islands are at the frontlines, but we know no country -- big or small -- is immune from increasingly severe, unprecedented weather impacts," he said.

The UN talks are seen as critical to laying the groundwork for a major new round of climate commitments due early next year.

Current pledges, even if implemented in full, would see the world warm a devastating 2.6 degrees Celsius this century, the UN has said, blasting past the internationally agreed limit of 1.5C since the pre-industrial era.

"Decisions in Baku could profoundly shape the climate trajectory and whether 1.5 degrees remains within reach," said Cosima Cassel of think tank E3G.

- Clash over cash -

Azerbaijan hosting the 11-22 November talks has drawn concerns over its heavy reliance on fossil fuels and its human rights record.

Countries last year committed to transition away from fossil fuels and triple renewables usage by 2030.

This year, negotiators must increase a $100 billion-a-year target to help poorer nations prepare for worsening climate impacts and wean them off coal, oil and gas.

The overall amount of this new goal, where it comes from, and who has access are major points of contention.

Experts commissioned by the UN estimate that developing countries, excluding China, will need to spend $2.4 trillion per year by 2030 on climate priorities.

From that, $1 trillion must come from international public and private finance.

Wealthy existing donors, including the EU and US, have said new sources of money will have to be found, including from China and oil-rich Gulf states.

China -- today the world's largest polluter and second-largest economy -- does pay climate finance but on its own terms.

Between 2013 and 2022, China paid on average $4.5 billion a year to other developing countries, the World Resources Institute said in a September paper.

Money could also be raised by pollution tariffs, a wealth tax or ending fossil fuel subsidies, among other ideas.

Rachel Cleetus, policy director of the Climate and Energy programme at the Union of Concerned Scientists, said negotiators in Azerbaijan should aim for a $1 trillion deal.

This money "is not charity", Cleetus told AFP, adding that it should mostly come as aid or very low interest loans to avoid adding to developing nations' debt.

"Nations either make those investments up front, or we'll be paying dearly for it after the fact, in disaster costs, in pollution costs. So this is a fork in the road. We have a choice," she told AFP.

- Green power -

Money was a key stumbling block for another major UN conference, although one that already lacks the US as a signatory.

Negotiations to halt humankind's destruction of nature ended Saturday in Colombia with no agreement on increasing funding for species protection.

A finance deal in Baku is seen as crucial to underpinning ambitious national climate pledges in the coming months.

Li said those pledges could be impacted by the US vote, with countries, including China, waiting to see the outcome before finalising longer-term targets.

Beyond Baku, there is also an "increasing interconnection between climate and the economic agenda", he said, including trade tussles between clean energy powerhouse China and the US and Europe.