Output data collected during the program. Trees Atlanta publicly reports the number and location of trees it plants, which we use to calculate the number of years of personal carbon emissions offset.

We estimate the number of years of carbon emissions the nonprofit offsets by comparing the trees actually planted by the nonprofit to the trees that would have been planted in the absence of the nonprofit (the “counterfactual”). Some trees would have been planted even without the nonprofit, such as by the government or other nonprofits; these counterfactual successes must be netted out of the successes we observe. Otherwise, we would be attributing a change (carbon emissions offset) to the nonprofit when it would have happened anyway. Few nonprofits estimate the counterfactual themselves, so we construct our own counterfactual estimate based on research and publicly available data. We use the percentage of plantable land left where the nonprofit works to calculate the probability of displacing the efforts of other organizations. We net out that change from the changes we observe to get a correct estimate of impact.

Analysis conducted by ImpactMatters and published on November 22, 2019.