imgAfforestationIcon Afforestation

Plant new forests and restore old forests. As trees grow, they draw carbon out of the air, which reduces the concentration of carbon dioxide. However, without care, large-scale afforestation can compromise biodiversity and historical land rights.


  • Government policies, incentives, and funding to identify available land, plant trees, and manage forests.

  • Business, land owner, and public support for large scale tree planting.

Big Message

  • Afforestation has the potential to pull significant amounts of carbon dioxide out of the atmosphere, but land availability and other effects should be considered. It would take an immense amount of land to make a large impact on temperature change.

Key Dynamics

  • Growing more trees boosts global removal of CO2 from the atmosphere, as photosynthesis pulls carbon into biomass and soils. Watch the temperature decrease modestly as a result.

  • Explore the graph “Land for Carbon Dioxide Removal.” The land area of India is 300 million hectares, so if we were to forest an area of that size we would still not see much change in temperature.

Potential Co-Benefits of Increasing Afforestation

  • New forests can create new ecosystems and protect existing wildlife habitats, biodiversity, and ecosystem services.

  • Larger and healthier tree canopies in cities reduce urban heat island effects and energy needed for heating and cooling.

  • Jobs are created in tree planting, care, and maintenance.

Equity Considerations

  • Afforestation entails shifting large areas of land into forests. This can sometimes result in monocultures of trees that are all the same age, which does not contribute to healthy biodiversity as much as natural forests.

  • Large shifts in land can compromise historic land access, so involving low-income and minority communities, including Indigenous peoples, in the process of policy development and implementation is essential.

Slider Settings

The Afforestation slider changes the percentage of available land that is used to grow new forests. 100% would mean that 700 Mha of land are covered in forests. 700 Mha represents approximately 25% of current grassland area, nearly 10% of all land that is not currently forest, and just over the difference in forest area back in 1850 until now (i.e., there is 630 Mha less forest area today than in 1850).

status quo

low growth

medium growth

high growth

Percent available land for afforestation

0% to +15%

+15% to +40%

+40% to +70%

+70% to +100%

Model Structure

The carbon sequestration of forests changes over time as the forest matures. Notice that net carbon removals are different than total removals due to carbon loss in older or unhealthy forests.

Maximum amount of available land: With a growing time of 80 years for new forests and 2%/year in total forest carbon loss, 700 Mha achieves an annual removal consistent with the mid-point of estimates of afforestation potential from the 2018 ‘Greenhouse gas removal’ report by the Royal Society (range of 3-20 in CO2 GtonsCO2/year).

For higher removals, one can adjust the “Afforestation settings” within the Assumptions view. For example, to explore the assumptions of the 2019 paper by Bastin et al., increase the slider “Max available land for afforestation” to 900mha under Assumptions.

Case Studies

New York City, USA: Increasing urban tree density by 343 trees per square kilometer was shown to reduce the rate of childhood asthma by 29% in New York City. 1

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Lovasi, G. S., Quinn, J. W., Neckerman, K. M., Perzanowski, M. S., & Rundle, A. (2008). Children living in areas with more street trees have lower prevalence of asthma. Journal of Epidemiology & Community Health, 62(7), 647–649.