Improved global wetland carbon isotopic signatures support post-2006 microbial methane emission increase

Atmospheric concentrations of methane, a powerful greenhouse gas, have strongly increased since 2007. Measurements of stable carbon isotopes of methane can constrain emissions if the isotopic compositions are known; however, isotopic compositions of methane emissions from wetlands are poorly constrained despite their importance. Here, we use a process-based biogeochemistry model to calculate the stable carbon isotopic composition of global wetland methane emissions. We estimate a mean global signature of -61.3 +/- 0.7 parts per thousand and find that tropical wetland emissions are enriched by similar to 11 parts per thousand relative to boreal wetlands. Our model shows improved resolution of regional, latitudinal and global variations in isotopic composition of wetland emissions. Atmospheric simulation scenarios with the improved wetland isotopic composition suggest that increases in atmospheric methane since 2007 are attributable to rising microbial emissions. Our findings substantially reduce uncertainty in the stable carbon isotopic composition of methane emissions from wetlands and improve understanding of the global methane budget.

Automated summary

This study calculates the isotopic composition of global wetland methane emissions using a model and finds that tropical wetland emissions have higher isotopic composition compared to boreal wetlands. The improved atmospheric simulation suggests that the increase in atmospheric methane since 2007 is due to rising microbial emissions.