Trump's attitude to climate change has drawn protests from all over the world
But former Mexican diplomat Patricia Espinosa said that the delay in any firm announcement suggests the issue is still unresolved.
She travels to US this weekend to try and meet the new US secretary of state.
'World will carry on'Ms Espinosa said it would be more damaging for the US to leave the on-going climate talks process altogether than to stop funding the clean energy program.
The US pays approximately $4m towards this program every year - and often an extra $2m in voluntary funding.
But she said the rest of the world would carry on tackling climate change without the US, if necessary.
She said China’s stated willingness to lead the world in curbing emissions might cause American diplomats to ponder the implications of allowing China a role of global moral leadership.
“We are of course worried about rumors that the possibility of the US pulling out of the Paris agreement and the convention on climate change,” she said.
“It would be very bad if there were a change of position in the US. That’s why I’m looking forwards to engaging with the US as a partner.”
She did not explain how the US would be able to remain within the Paris framework whilst scrapping action on its own emissions strategy that helps underpin that process.
Embracing green actionBut she drew hope from the vast number of firms and cities looking towards a low-carbon future - in the US and around the world: "A lot of US businesses are really going into the agenda of sustainability and some are making their own commitments in emissions reductions in their own operations."
“An incredible amount of cities have embarked on ambitious goals; some states like California have been for many years in the forefront of this agenda.
“In International Petroleum Week, I was very encouraged to hear how much some of the oil and gas companies are realising that the future of their industries is in a transformation into clean energy companies - and they have embraced this in their own interest.
“The transformation has started. I think it’s unstoppable.”
Ms Espinosa smiled at the irony of dealing with Mr Trump as a Mexican, a woman, and someone who works in climate change.
She said her trip to the US would include meeting businesses and civil society groups and - hopefully - a senior member of the administration. She is anticipating a meeting with the new secretary of state Rex Tillerson.
The former CEO of the oil giant Exxon Mobil warned recently that climate change is a genuine risk, and said the US should stay at the table of UN talks.
Other nations have responded differently to the new situation presented by Mr Trump. China has offered to lead and India has surprised many with its new level of ambition.
Saudi Arabia has expressed support for a slower rate of decarbonization and Russia - the fifth largest emitter - has not yet ratified the climate deal from Paris.