Study of atmospheric CO and CH4 trends and their response on global climate changes based on experimental data and model simulations

Based on the analysis of orbital measurements and GEOS-Chem model calculations with different anthropogenic and wild-fires emission scenarios, a study of trends in the total content of CO and CH₄ in different periods and seasons of 2003-2023 for the Eurasia domain, -20°E - 180°E, 0°N - 80°N. A response of CO trends to climate change was estimated. Data from the orbital AIRS instrument and ground-based spectrometers were used as experimental information to assess atmospheric composition trends.
A good agreement has been established between estimates obtained from the orbital data and from simulations. However, certain regional features of the discrepancies have been identified and are associated with the inaccuracy of specifying the spatial distribution and integral power of anthropogenic CO, CH4 and another species emission and their trends for Russia, South-East Asia and other regions of Eurasia. These emission uncertainties affect the accuracy of model calculations.
In general, according to average annual estimates, CO TC trends over entire Eurasia for 2000-2023 was slightly negative (~ 0.5-1.2 %/year depending on the region); however, after approximately 2008 the downward trend slowed down, and in some areas the CO TC began to rise.
Thus, a positive change in CO TC trends after about 2008 was established. In the entire domain under study, this change was about 2–3%/year, according both experimental and model estimates. In autumn months of 2008-2023 the increase in CO TC was established over almost the entire Eurasia, including Arctic regions and Europe. This growth (at least in Europe) cannot be explained by either anthropogenic emissions or releases from wild-fires. A possible reason for this rising may be the formation of additional CO from methane, the increase in concentrations of which began around the same time (after 2007), and change in the source/sink ratio for CO.
Additionally, to assess the parameters of correspondence between orbital and ground-based measurements, we have compared the trend estimates using only synchronous orbital and ground-based CO and CH₄ observations and obtained the drift of the difference between them.
The study was supported by Russian Science Foundation under grant №20-17-00200.