A global atmospheric methane record from a tropical ice core

Abstract

Tropical wetlands are widely considered the largest natural source of atmospheric methane (CH4)1, 2, 3–4. However, uncertainties about wetland extent and CH4 production have led to large variations in modelled CH4 emission trends2,3. Most historical reconstructions rely on data from polar ice cores, which cannot fully resolve the tropical contribution5,6 to the CH4 budget. Here we present a 2,000-year record of atmospheric CH4 concentrations from ice cores drilled from the South Peak summit of Nevado Huascarán (Summit Core A, SCA; −9.122° S, −77.605° W; 6,768 m asl). We find that the trends and magnitudes of our CH4 record are broadly consistent with polar records7. Our δ13C-CH4 measurements (from approximately 1530 CE to 1999 CE) align with isotope values8 consistent with a dominant tropical CH4 source. Integration of our record into an atmospheric four-box model suggests a sustained equatorial dominance of CH4 source strength over the past two millennia. Our findings indicate that equatorial CH4 emissions are higher than previous estimates based only on polar ice core data, supporting the long-standing hypothesis that low-latitude CH4 emissions dominated pre-industrial (PI) CH4 variability5,6. These results demonstrate the importance of tropical ice cores on the reconstruction of CH4 variability and latitudinal distribution. A 2,000-year Peruvian ice core record of atmospheric CH4 concentrations contains the first historical global CH4 record from the low latitudes, and implementation of a four-box model indicates higher equatorial CH4 strength than previous estimates from polar-only records.