A global atmospheric methane record from a tropical ice core

Tropical wetlands are widely considered the largest natural source of atmospheric methane (CH 4 ) 1–4 . However, uncertainties about wetland extent and CH 4 production have led to large variations in modelled CH 4 emission trends 2,3 . Most historical reconstructions rely on data from polar ice cores, which cannot fully resolve the tropical contribution 5,6 to the CH 4 budget. Here we present a 2,000-year record of atmospheric CH 4 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 CH 4 record are broadly consistent with polar records 7 . Our δ 13 C-CH 4 measurements (from approximately 1530 CE to 1999 CE) align with isotope values 8 consistent with a dominant tropical CH 4 source. Integration of our record into an atmospheric four-box model suggests a sustained equatorial dominance of CH 4 source strength over the past two millennia. Our findings indicate that equatorial CH 4 emissions are higher than previous estimates based only on polar ice core data, supporting the long-standing hypothesis that low-latitude CH 4 emissions dominated pre-industrial (PI) CH 4 variability 5,6 . These results demonstrate the importance of tropical ice cores on the reconstruction of CH 4 variability and latitudinal distribution.