The amount of carbon that additional trees can pull out of the atmosphere is overshadowed by the enormous amount of carbon dioxide released through fossil fuel combustion. This is one of the main reasons why planting lots of trees is limited in the impact it has on climate.
See the graph "Greenhouse Gas Net Emissions by Gas" to compare the scale of CO2 emitted by fossil fuels to the scale of CO2 emitted by deforestation or removed by afforestation ("land use CO2"). For example, here is a scenario in which deforestation ends by 2050 and we plant 700 million hectares of land with trees. Explore this scenario in En-ROADS.
In addition, the amount of land needed for afforestation to make even a modest impact on climate would be enormous—for example, it would be on the scale of the area of India, one of the largest countries in the world. See the graph “Land for Growing CO2-Removal Biomass.”
To learn more about the impact of afforestation on climate change and how it is modeled in En-ROADS, see our article here: Can trees solve the climate crisis? Unfortunately, No. Note on Bastin et al.’s erratum (2020)