"On 12 December [...] I will organise a new summit in order to take new action for the climate, including on the issue of financing," Macron said, noting that the date is the second anniversary of the Cop21 Paris climate agreement.
It will attempt to facilitate the payment of private and public finance promised during those talks, he said.
It will also "identify projects that can be financed and will represent a concrete advance".
The G20 final statement noted the US's decision to pull out of the Paris deal but insisted that "the leaders of the other member states confirm that the Paris accord is irreversible".
Macron said that there could be no going back on climate questions, warning that the accord could not be taken "à la carte".
Asked if he hoped to change Trump's mind when the US president attends next week's Bastille Day parade in Paris, Macron commented "I never give up hope of convincing, because I think it is a duty [...] it's part of my character.
"So I confirm, I hope to convince him."