A consistent climate data record of atmospheric methane from the GOSAT and GOSAT-2 missions

Abstract. Understanding the renewed and accelerating growth of atmospheric methane requires satellite records that are long enough to span decadal change and consistent enough that instrumental differences are not mistaken for atmospheric signals. We present version 2.0 of the University of Leicester Proxy retrieval of column-averaged dry-air methane (XCH₄) from the GOSAT-2 TANSO-FTS-2 instrument, comprising approximately 4.4 million quality-filtered soundings in land nadir and ocean glint observation modes between 5 February 2019 and 31 December 2025. The data are processed with the same algorithm, a priori fields, and quality-filtering framework as the established GOSAT Proxy v10.0 product, with the aim of producing a consistent multi-instrument climate data record. The on-board intelligent pointing of GOSAT-2 improves the yield of usable land soundings, particularly at coastal and island sites. The GOSAT-2 bias correction is cross-anchored to GOSAT over 124,206 matched-pair footprints and depends linearly on solar zenith angle. Anchoring to GOSAT rather than directly to the Total Carbon Column Observing Network (TCCON) leaves the corrected GOSAT-2 with a residual mean TCCON bias of +5.52 ppb, in exchange for sub-ppb inter-instrument consistency over the overlap period. Validation against the TCCON GGG2020.1 release yields a standard deviation of the satellite-minus-TCCON differences of 16.41 ppb and a correlation coefficient of 0.910 across 135,110 co-locations at 24 sites, compared to 16.42 ppb and 0.950 for GOSAT over 25 sites, demonstrating that GOSAT-2 reaches the precision of the heritage instrument. Co-located monthly 2° grid-cell means from GOSAT and GOSAT-2 during the 2019–2025 overlap correlate at 0.95 (land) and 0.97 (glint), with mean biases of +1.9 and +3.0 ppb. Beyond the cross-anchored correction, no further adjustment for either observation mode is required to merge the two records. The combined record forms a continuous Proxy XCH₄ time series spanning 2009 to 2025, which will be extended as both missions continue to operate, and provides a reference for inter-comparison with TROPOMI and the next generation of greenhouse-gas monitoring missions. The GOSAT-2 Proxy XCH₄ v2.0 dataset is available from the Centre for Environmental Data Analysis at https://doi.org/10.5285/8209b9acb92e4ba69188c9c8ff7a3b76 (Parker et al., 2026a).