Changes of Atmospheric CO2 in the Tibetan Plateau From 1994 to 2019

The importance of carbon neutrality and green development rose sharply in the post-pandemic era in China. This study investigated the long-term variability of atmospheric carbon dioxide (CO2) in China using CO2 records from Mount Waliguan (WLG), the only global station of World Meteorological Organization/Global Atmosphere Watch in Eurasia, covering a 26-year period (1994-2019). Overall, the atmospheric CO2 mole fraction increased continuously and steadily with a growth rate of 2.15 +/- 0.01 ppm yr(-1) over 1994-2019 at WLG. The average CO2 mole fraction was only 359.9 +/- 0.04 ppm in 1994, but reached a historic level of 414.9 +/- 0.04 ppm by 2019. The mean growth rates in city sectors (data from the city regions) were slightly higher than that in the Tibetan Plateau. The seasonal amplitude of atmospheric CO2 at WLG was lower than those at adjacent regional stations, such as Lin'an, and Shangdianzi, but larger those at global stations Mauna Loa and Minamitorishima. Potential strong source regions moved from urban areas to the southwest region away from WLG, suggesting the potential emergence of Northern India as a strong CO2 source region. The area of potential CO2 sources at WLG prominently expanded with time, reflecting the effect of more intensifying anthropogenic emissions in recent decades. Although numerous measures for carbon emission reduction have already been implemented, it is clear that much work, e.g., carbon emission estimation, sources/sinks tracing, cleaner energy technologies, remains to be done in order to achieve carbon emission peak and carbon neutrality set by the Chinese government. Plain Language Summary To achieve carbon emission peak and carbon neutrality set by the Chinese government, it is important to understand the long-term variability of atmospheric carbon dioxide (CO2) in China. Hence, we first presented 26-year CO2 records observed at Mount Waliguan (WLG) station. We found that the CO2 concentration increased continuously and steadily over 1994-2019 at WLG. The characteristics of CO2 changed over different observing periods. The increasing trend in the Tibetan Plateau was even similar to that in city regions over different periods. Northern India is likely becoming a strong source area to WLG. The area of potential sources also increased with time. Hence, there is still a lot of work to be done to achieve the goal of carbon emission reduction in China.