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 graphs “CO2 Emissions from Fossil Fuels and “CO2 Removal from Afforestation to compare the scale of afforestation removals to the scale of CO2 emitted by fossil fuels.

For example, here is a scenario in which we plant 700 million hectares of land with trees (afforestation). CO2 emissions from fossil fuels reach 43 Gt CO2/year by 2100, while net CO2 removal due to afforestation (the blue line) is only 6.3 Gt CO2 per year by 2100.

You can also compare the “Greenhouse Gas Net Emissions by Gas” graph with and without this action. Afforestation reduces the green “Land Use CO2” wedge by removing some of the CO2 released by deforestation and bioenergy.

In addition, the amount of land needed for afforestation to make even a modest impact on climate would be enormous—for example, 700 Mha is over twice the area of India, one of the largest countries in the world. See the graph Land for Growing CO2-Removal Biomass under Graphs > Land, Forestry, and Food.

To learn more about the impact of afforestation on climate change and how it is modeled in En-ROADS, see our articles here: