The large role of declining atmospheric sulfate deposition and rising CO2 concentrations in stimulating future wetland CH4 emissions

Existing projections of wetland methane emissions usually neglect feedbacks from global biogeochemical cycles. Using data-driven approaches, we estimate wetland methane emissions from 2000 to 2100, considering effects of meteorological changes and biogeochemical feedbacks from atmospheric sulfate deposition and CO 2 fertilization. In low-CO 2 scenarios (1.5° and 2°C warming pathways), the suppressive effect of sulfate deposition on wetland methane emissions largely diminishes by 2100 due to clean air policies, with resulting emission increases (7 ± 2 Tg a −1 ) being 35 and 22% of total wetland emission changes. In mid-CO 2 scenarios (2.4° to 3.6°C warming pathways), sulfate deposition changes modestly, and CO 2 fertilization contributes >30% of wetland emission increases. Across all scenarios, biogeochemical feedbacks can stimulate 30 to 45% of future wetland emission rises. Under 1.5° and 2°C pathways, wetland methane emissions will likely increase by 20 to 34 Tg a −1 by 2100, representing 8 to 15% of the allowable space for anthropogenic methane emissions, a factor not yet considered by current assessments.