In the boreal forests of northern Mongolia, 1.2 million hectares of forest have regenerated in the last 20 years, while other regeneration hotspots include central Africa and the boreal forests of Canada.
But the researchers warned that forests across the world face "significant threats".
Despite "encouraging signs" with forests along Brazil's Atlantic coast, deforestation is such that the forested area needs to more than double to reach the minimal threshold for conservation, they said.
The project is a joint venture between WWF, BirdLife International and WCS, who are calling on other experts to help validate and refine their map, which they regard as "an exploratory effort".
One of the simplest ways to remove carbon dioxide from the air is to plant trees. But scientists say the right trees must be planted in the right place if they are to be effective at reducing carbon emissions.