Chinese scientists have proven that when methane (CH₄) emissions increase by the same amount in East Asia and North America, the effects on atmospheric circulation and ozone (O₃) are different. The study was published in Advances in Atmospheric Sciences. 

The effects of an increase in CH₄ concentration on atmospheric radiation and chemistry have been extensively studied. However, the chemistry–radiation–dynamic interactions associated with CH₄ increases have not been resolved well in previous modeling studies, largely due to the limitation of model performance in the stratosphere. Additionally, while most previous studies have investigated the effects on climate and stratospheric O₃ of global-scale CH₄ emission increases, the less well-studied effect of a CH₄ emissions increase in East Asia on global temperature and O₃ remains a popular but controversial issue. 

Fig. 1. Latitude–height cross sections of the O₃ differences (units: ppbv) when (a) CH₄ emissions increase by 50% in East Asia, (b) CH₄ emissions increase by 50% in North America, and (c) CH₄ emissions increase by 15% on the global scale, relative to the control experiment (E0). Shaded regions show where the differences are statistically significant at the 90% confidence level, using the Student’s t-test. (Image plotted by LIU Yi et al)

Using a fully coupled chemistry–climate model (WACCM3), the study, led by Dr. LIU Yi, under a collaboration among the Institute of Atmospheric Physics, Lanzhou University, and Shandong Provincial Climate Centre, shows that the Brewer–Dobson circulation in the tropics between 10°S and 10°N at 100 hPa weakens as CH₄ emissions increase in East Asia, but strengthens when CH₄ emissions increase in North America. 

When CH₄ emissions increase by 50% in East Asia and North America, the maximum increase of stratospheric O₃ is 45 ppbv and 60 ppbv, respectively (Fig. 1). So, a CH₄ emissions increase in North America has a greater influence on the stratospheric O₃ than the same CH₄ emissions increase in East Asia. 

When CH₄ emissions increase in East Asia, the increase in the tropospheric O₃ concentration is largest in August. When CH₄ emissions increase in North America, the increase in the O₃ concentration is largest in July in the mid-troposphere, and in April in the upper troposphere.