Wetland Restoration as a Nature-Based Climate Solution: Quantifying Methane Emissions and Climate Feedbacks

Limiting future global warming and achieving net zero emissions will require significant reductions in greenhouse gas (GHG) emissions alongside deployment of nature-based carbon dioxide (CO2) removal strategies. However, warming-induced emissions from natural ecosystems can introduce positive climate feedbacks that diminish mitigation potential and reduce the remaining carbon budget. Wetlands are a key example of this challenge. While wetland restoration is widely proposed as a nature-based climate solution as it can enhance CO2 sequestration, wetlands are also the largest natural source of methane (CH4), a potent GHG and key driver of atmospheric chemistry. Rising temperatures may amplify wetland CH4 emissions, offsetting CO2 uptake from restoration efforts and resulting in positive climate feedbacks, with potential implications for air quality and Earth system stability. Quantifying these feedbacks is critical for evaluating the net climate effectiveness of wetland-based mitigation. In this work, we investigate how large-scale global wetland restoration affects future CH4 emissions, atmospheric composition and climate under two warming pathways. Using historically reconstructed wetland areas, we develop two global wetland scenarios: protection of current wetlands, and restoration to 1900 coverage by 2050 with protection thereafter. Wetland CH4 emissions are estimated using an offline emission scheme driven by soil respiration and temperature outputs from eight CMIP6 Earth System Models under SSP1-2.6 (2°C warming and lower air pollution) and SSP3-7.0 (4°C warming and higher air pollution). These emissions are implemented in a CH4 emission-driven version of the UK Earth System Model (UKESM) to simulate responses in atmospheric CH4 mixing ratio, oxidising capacity and air quality. Associated climate impacts are evaluated by quantifying changes in the net GHG balance and radiative forcing, accounting for carbon sequestration and avoided drained emissions.We find that wetland restoration amplifies warming-driven CH4 emissions, by 57% (91 Tg yr-1)  under SSP3-7.0 and by 30% (48 Tg yr-1) under SSP1-2.6 by 2100. In comparison, protecting wetlands at current levels leads to smaller increases (33% and 11%, respectively). As a result of enhanced CH4  emissions, wetland restoration increases atmospheric CH4 mixing ratios by approximately 100 ppb under SSP1-2.6 and 145 ppb under SSP3-7.0. While global impacts on air pollutants such as ozone and particulate matter are small, more substantial regional impacts may have implications for human health. Our results provide a comprehensive assessment of wetland restoration as a climate strategy under future warming, highlighting its potential to deliver net-zero goals while also identifying important trade-offs and implications for mitigation and policy.