Prioritizing forestation based on biogeochemical and local biogeophysical impacts

Reforestation and afforestation is expected to achieve a quarter of all emission reduction pledged under the Paris Agreement. Trees store carbon in biomass and soil but also alter the surface energy balance, warming or cooling the local climate. Mitigation scenarios and policies often neglect these biogeophysical (BGP) effects. Here we combine observational BGP datasets with carbon uptake or emission data to assess the end-of-century mitigation potential of forestation. Forestation and conservation of tropical forests achieve the highest climate benefit at 732.12 tCO2e ha–1. Higher-latitude forests warm the local winter climate, affecting 73.7% of temperate forests. Almost a third (29.8%) of forests above 56° N induce net winter warming if only their biomass is considered. Including soil carbon reduces the net warming area to 6.8% but comes with high uncertainty (2.9–42.0%). Our findings emphasize the necessity to conserve and re-establish tropical forests and consider BGP effects in policy scenarios. Forests take up carbon from the atmosphere but also change Earth’s surface energy balance through biophysical effects. Accounting for these shows that tropical forests have the highest mitigation potential; the climate benefit of higher-latitude forests is offset by their warming effects in winter.