Supporting information available with version of record. ; Using methane and carbon dioxide atmospheric mixing ratios retrieved using SWIR spectra from the Greenhouse Gases Observing SATellite (GOSAT), we report the first wildfire plume CH4 to CO2 emission ratios (ERCH4/CO2) determined from space. We demonstrate the approach’s potential using forward modeling and identify a series of real GOSAT spectra containing wildfire plumes. These show significantly changed total-column CO2 and CH4 mixing ratios, and from these we calculate ERCH4/CO2 for boreal forest, tropical forest, and savanna fires as 0.00603, 0.00527, and 0.00395 mol mol 1 , respectively. These ERs are statistically significantly different from each other and from the “normal” atmospheric CH4 to CO2 ratio and generally agree with past ground and airborne studies. ; We thank JAXA, NIES, and MOE for GOSAT data and their support as part of the Joint Research Agreement. R.P. and M.J.W are supported by the NERC National Centre for Earth Observation (NCEO). R.P. is also supported by the ESA Climate Change Initiative, and M.J.W by the EU Seventh Research Framework Programme (MACC-II project, contract 283576). We also thank BADC for providing ECMWF Operational Analyses data used in retrievals. ; Peer-reviewed ; Publisher Version