En-ROADS User Guide

Afforestation and Reforestation🔗

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 for newly planted trees to remove enough carbon for it to be a significant source of carbon removals.

  • Reversibility. Trees are susceptible to fire, insects, and weather-related damage, not to mention future harvests; all of which lead to carbon emissions as a result of combustion and decay.

  • 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.

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🔗

Forests are dynamic and result in both carbon removals and emissions. Notice in the “CO2 Removal from Afforestation” graph that net CO2 removals are lower than total removals due to the carbon loss from decay and forest fires in older or unhealthy forests.

Maximum amount of available land: For higher removals, one can adjust the “Max available land for afforestation” under 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.

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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