The Washington Post Shared Our Analysis of A Trillion Trees - Here’s What’s Behind the Numbers

August 2, 2023 by Climate Interactive

In response to House Speaker Kevin McCarthy’s proposal to plant a trillion trees, Maxine Joselow of the Washington Post wrote an article that included analysis from Climate Interactive’s En-ROADS simulator.

Below is background information on the simulator, notes on the settings in En-ROADS required to replicate the findings that were quoted in the article, and other supporting assumptions and calculations.

To learn more about these calculations view our webinar recording, A Trillion Trees: Calculating the Mitigation Potential in the En-ROADS Simulator. For more insights into land availability, read this opinion column featured in The Messenger, written by Executive Director Andrew Jones and Joseph Romm, Ph.D.

Background on the En-ROADS Simulator

The En-ROADS Climate Solutions Simulator is a tool for understanding how we can achieve our climate goals through global changes in energy, land use, consumption, agriculture, and other policies. It is designed to provide a synthesis of the best available science on climate solutions and put it at the fingertips of groups in policy workshops and role playing exercises. Led by the team at Climate Interactive, En-ROADS has benefited from a close collaboration with the MIT Sloan Sustainability Initiative, as well as many others.

For additional information on En-ROADS, please explore these resources:

Previous versions of En-ROADS have been used to examine whether trees can solve the climate crisis, including an analysis of Bastin et al. (2019), and the role afforestation plays in addressing climate change.

Below are notes on the calculations behind the Washington Post article.

Notes on “…planting a trillion trees would only prevent 0.15 degrees Celsius (0.27 Fahrenheit) of warming by 2100”

In the trillion trees scenario produced in En-ROADS, two sliders have been moved: 1) Under the Simulation > Assumptions > Carbon capture and removals: Afforestation settings, the “Max available land for afforestation” is increased to 900 MHa and 2) Under Afforestation > “Percent available land used for afforestation“ is set at 100%. The temperature result in 2100 is shown under Graphs > Impacts > Temperature Change.

Notes on “…planting a trillion trees would only sequester 6 percent of the carbon dioxide that the world needs to avoid emitting by 2050 to meet the goal of the Paris climate accord…”

In the trillion trees scenario in En-ROADS, the cumulative CO2 emissions in 2050 are 37 gigatons (from 3653 gigatons in the Baseline Scenario to 3616 gigatons) lower. View the graph under Graphs > CO2 Emissions > Cumulative CO2 Net Emissions.

To limit warming to 1.5°C by 2100 (example scenario here), the cumulative CO2 emissions in 2050 would need to fall by 614 gigatons in 2050 (from 3653 gigatons in the Baseline Scenario to 3039 gigatons in 2050 in the 1.5℃ scenario). The 37 gigatons from the trillion trees is 6% of the required 614 gigatons of CO2 reduction in 2050.

Notes on “…planting a trillion trees would require an enormous amount of land — 900 million hectares, or nearly three times the size of India.”

To plant a trillion trees, we estimated it would take approximately 900 million hectares of land based on a survey of studies. For example, the 2020 study by Russell in Significance, the journal of the Royal Statistical Society, estimates that planting one trillion trees would require 400 to 1600 Mha depending on the planting density1.

To learn more about testing afforestation scenarios in En-ROADS, check out:

Notes on “…avoiding the same amount of carbon dioxide emissions by building more wind and solar farms would require only 15 million hectares by 2050…”

Planting trees on 900 million hectares would avoid 37 gigatons of net CO2 emissions by 2050 according to En-ROADS (see scenario). To reduce CO2 emissions in 2050 by the same amount with wind and solar energy rather than by planting trees, would require only 15 million hectares of additional land by 2050, as opposed to 900 million hectares.

To get the estimate that 15 million hectares of additional land are needed by 2050 for solar and wind energy, we created a scenario in En-ROADS where renewable energy provides the equivalent emissions reductions by 2050 as planting a trillion trees (see the scenario). In this scenario, renewables are subsidized by $0.02/kWh in En-ROADS, which means the electricity production capacity from wind increases from 1322 gigawatts to 1852 gigawatts, and solar increases from 1757 gigawatts to 2349 gigawatts.

Given estimated land densities of wind and solar capacity of 25 hectares/megawatt and 3 hectares/megawatt, respectively2 3 4, achieving the needed increases in renewable capacity by 2050 would require 13.2 million hectares of wind and 1.8 million hectares of solar, for a total of 15 million hectares by 2050.

To learn more about testing renewable energy scenarios in En-ROADS check out:

To explore what action is needed to effectively limit climate change, test out a variety of climate solutions in En-ROADS and create your own scenario.


  1. Russell, M. (2020). Do forests have the capacity for 1 trillion extra trees? Significance, Vol. 17, Issue 6.

  2. Denholm, P., Hand, M., Jackson, M., & Ong, S. (2009). Land-use requirements of modern wind power plants in the United States. National Renewable Energy Laboratory (NREL).

  3. Harrison-Atlas, D., Lopez, A., & Lantz, E. (2022). Dynamic land use implications of rapidly expanding and evolving wind power deployment. Environmental Research Letters, 17(4), 044064.

  4. Ong, S., Campbell, C., Denholm, P., Margolis, R., & Heath, G. (2013). Land-use requirements for Solar Power Plants in the United States. National Renewable Energy Laboratory (NREL).