The remote extratropical Southern Hemisphere (SH) has the cleanest atmosphere on Earth, but is subject to rapid changes regarding the emissions landscape and a warming climate, which strongly impact local atmospheric composition. Carbon monoxide (CO) is a product of methane (CH4) oxidation and a modulator of the tropospheric oxidizing capacity. In this study we investigate if the rapid increase in tropospheric CH4 levels of ∼7 % between 2008 and 2022 has driven a positive response in CO in the remote SH, based on multi-platform observations and a global chemistry transport model. We find inconsistencies in observations from aircraft, surface and satellite. CSIRO surface flask observations, AGAGE in-situ measurements (2008–2022) and airborne observations from the HIPPO (2009–2011) and ATom (2016–2018) campaigns show CO increases of 5–10 %. CO columns inferred from IASI (2014–2023) show more moderate increases of 3–4 % (statistically insignificant). NOAA surface flask observations and CO columns from MOPITT (2008–2022) do not show changes over time. GEOS-Chem simulations are consistent with the observed positive trend, exhibiting a significant CO increase of ∼7 % throughout the southern extratropical troposphere (2008–2022). These CO increases are partly driven by enhanced production from rising CH4 (∼50 %) and further affected by increases in biogenic non-methane volatile organic compounds (NMVOC) (∼45 %) and the direct effects of rising temperatures (∼5 %). We further explore how simulated CO levels in the remote SH could be impacted by future enhancements in primary and precursor emissions, changes in the oxidizing capacity, and temperature.