The Committee on Climate Change (CCC) recommends 30,000 hectares of woodland should be planted annually, more than double the new trees planted last year.
And it said this may have to rise to 50,000 hectares if other carbon reduction targets are not achieved.
The government said it planned to “rapidly grow forest cover”.
he committee – made up of experts in science, economics, and business – said this required woodland to increase from 13% of land in the UK to 17%.
Charity the Woodland Trust said this would be equivalent to about 1.5 billion new trees and that future generations would be “let down” by poorer air quality and rising “urban heat” if the committee’s targets were not met.
The CCC said 30,000 hectares (116 sq miles) of new trees are needed per year until 2050.
This is equivalent to filling more than 46,000 standard football pitches or a space about three-quarters the size of the Isle of Wight every year.