Global “Climate Opportunity Benefit” of Forest Regeneration: Meta‐Analysis Shows Warming From Soil CH ₄ and N ₂ O Is Small Relative to Agriculture

Abstract Global assessments of ecosystem regeneration as a climate mitigation strategy have traditionally focused on CO 2 , despite the acknowledgment that methane (CH 4 ) and nitrous oxide (N 2 O) are also important greenhouse gases (GHGs). We conducted a meta‐analysis of studies that measured soil CH 4 and N 2 O fluxes in unmanaged, regenerating forested and savanna ecosystems, with a focus on understanding biome‐specific differences in these GHG fluxes compared to a counterfactual of agricultural land use. We expected most regenerating ecosystems to act as small CH 4 sinks and relatively larger N 2 O sources, with a net warming combined CH 4 ‐N 2 O effect. Three of the five forested biomes we studied followed this pattern: subtropical/tropical forest, subtropical/tropical savanna and temperate conifer forest (0.60 ± 0.30, 0.15 ± 0.06, and 0.83 ± 0.24 Mg CO 2 e ha −1 yr −1 , respectively). Results suggest that even after 100 years of regeneration, the radiative cooling of the climate from CO 2 sequestration in aboveground biomass exceeds the radiative warming driven by the net CH 4 ‐N 2 O effect among all ecosystems on average globally. We also found that the “climate opportunity benefit” of ecosystem regeneration—the difference in the net CH 4 ‐N 2 O effects of agriculture versus regeneration—yields a net cooling effect for all biomes. However, because the CH 4 ‐N 2 O effect diminishes the cooling effect of ecosystem regeneration, our results underscore that it is unsound to use ecosystem regeneration as a justification for continuing fossil fuel emissions.