En-ROADS User Guide


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 Messages🔗

  • 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🔗

  • Impact. 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.

  • Delay. It takes decades or more for newly planted trees to become large enough to remove significant amounts of carbon from the atmosphere.

  • Reversibility. Trees do not live forever, and when they die or are cut down, their stored carbon eventually returns to the atmosphere.

  • Scale compared to emissions from energy. 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.

  • Land needed. Explore the graph “Land for Growing CO2 Removal Biomass.” The land area of India, represented by the dotted line, is approximately 329 million hectares.1 Even 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 to forest. 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 historical land access, so involving low-income and minority communities, including Indigenous peoples, in the process of policy development and implementation is essential.


Afforestation & Technological CO2 Removal

Slider Settings🔗

The Afforestation slider changes the percentage of available land that is used to grow new forests. 100% would mean that 700 million hectares (Mha) of land is covered in forests. 700 Mha represents approximately 21% of current grassland area, 8% of all land (including desert and tundra) that is not currently forest, and just over the difference in forest area back in 1850 until now (i.e., there is 680 Mha less forest area today than in 1850).2

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 Gtons CO2/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 900 Mha 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.3


Please visit support.climateinteractive.org for additional inquiries and support.


[1]: United Nations. (2020). Demographic Yearbook. Table 3.

[2]: Hurtt, G. C., L. Chini, R. Sahajpal, S. Frolking, B. L. Bodirsky, K. Calvin, J. C. Doelman, J. Fisk, S. Fujimori, K. K. Goldewijk, T. Hasegawa, P. Havlik, A. Heinimann, F. Humpenöder, J. Jungclaus, Jed Kaplan, J. Kennedy, T. Kristzin, D. Lawrence, P. Lawrence, L. Ma, O. Mertz, J. Pongratz, A. Popp, B. Poulter, K. Riahi, E. Shevliakova, E. Stehfest, P. Thornton, F. N. Tubiello, D. P. van Vuuren, X. Zhang (2020). Harmonization of Global Land-Use Change and Management for the Period 850-2100 (LUH2) for CMIP6. Geoscientific Model Development Discussions.

[3]: 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.

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