A UN climate conference dominated by Donald Trump's threats to withdraw from a hard-won pact concludes in Marrakesh Friday amid fears that the goal of curtailing worst-case-scenario global warming may not be achieved without US backing.

The first gathering of the UN's climate forum since last year's adoption of the Paris Agreement to curtail disastrous global warming, was tasked with drafting a roadmap for its execution.

It has been overshadowed by uncertainty about US president-elect Trump's vow to "cancel" the pact to rein in greenhouse gas emissions blamed for warming.

On Thursday, the eve of the conference's closure, the nearly 200 parties to the UN's climate convention made a rare united appeal for "the highest political commitment" to combat climate change.

"Our climate is warming at an alarming and unprecedented rate and we have an urgent duty to respond," they said in the "Marrakesh Action Proclamation".

"We call for the highest political commitment to combat climate change, as a matter of urgent priority."

Many fear that Trump, who has described climate change as a "hoax" perpetrated by China, will act on his threat to withdraw from the pact, thus ruining years of painstakingly-negotiated political goodwill.

Worse, a US withdrawal would leave the cause without billions of dollars of finance for developing countries to make the shift to clean energy or the means to shore up defences against climate change impacts that can no longer be avoided.

- 'Scary' -

"There's no doubt that if Mr Trump makes sharp cuts to the federal government support of developing countries that will be noticed and have an impact," veteran climate negotiations analyst Alden Meyer of the Union of Concerned Scientists told AFP.

The Paris pact sets the goal of limiting average global warming to 2.0 degrees Celsius (3.6 degrees Fahrenheit) over pre-Industrial Revolution levels, by cutting greenhouse gases from burning fossil fuels.

Countries, including the United States, have pledged to curb emissions under the deal by shifting to renewable energy sources.

But Trump has vowed to boost oil, gas and coal.

Experts say warming over 2C will result in land-gobbling sea level rise, worsening storms and droughts, disease spread and conflict over ever-scarcer resources.

Highlighting the stakes, US government scientists said Thursday that the first 10 months of the year were the hottest in modern times -- and 2016 will likely surpass 2015 as the warmest year on record.

According to scientists, the world is headed for warming of 3C, or more on current emissions-curbing pledges.

Without the US, delegates and analysts say, the goal will be even harder to reach.

"The chances of the rest of the world contributing the emissions reductions commitments that the US is required to undertake, or covering the shortfall in climate finance that the US is required to contribute, is unlikely to happen," said Mohamed Adow of Christian Aid, which monitors the climate negotiations on behalf of poor countries.

"That is scary."

While waiting for the in-coming US president to make his climate position clear, many now look to the rest of the world to bolster the Paris Agreement.

In a "high-level segment" of the gathering, starting with heads of state and government on Tuesday and ministers over the following two days, speaker after speaker recommitted their nations to the pact.

On Thursday, the BASIC group of Brazil, South Africa, India and China, stressed they would "continue and strengthen" their own actions, while stressing "there can be no backtracking on commitments from developed countries and no attempt to renegotiate the terms of the agreement reached in Paris".