This work that explores the chemistry-climate implications of adding chlorine to the atmosphere as a climate intervention technique.

About 40-45% of the increase in radiative forcing from 1750 to 20019 is due to the direct and indirect effects of methane, which has roughly equal anthropogenic and natural origins thus making emission control a difficult task. Methane is mostly removed from the atmosphere through the reaction with OH and to a lesser extent through the reaction with chlorine atoms. Based on this, some studies have proposed intentionally adding chlorine to the atmosphere to reduce methane concentrations. However, the environmental impacts of adding chlorine to the atmosphere remain unexplored.

This work led by IQF-CSIC conducts a first evaluation of how much chlorine would be needed to reduce methane and assesses the resulting changes in global atmospheric composition and radiative forcing by 2050. Because of non-linear chemistry-climate interactions, the atmospheric composition and radiative balance are heavily perturbed in a short period of time (i.e. few decades) when large amounts of chlorine are added, leading to a significant decrease in methane and ozone, which in turn leads to a temperature decrease. The paper concludes that the environmental impacts (particularly on air quality, stratospheric ozone and ocean acidity) of this currently proposed global warming mitigation technique must be carefully considered before any action is taken. The results are published in Nature Communications.

Qinyi Li, Daphne Meidan, Peter Hess, Juan A. Añel, Carlos A. Cuevas, Scott Doney, Rafael P. Fernandez, Maarten van Herpen, Lena Höglund-Isaksson, Matthew S. Johnson, Douglas E. Kinnison, Jean-François Lamarque, Thomas Röckmann, Natalie M. Mahowald, and Alfonso Saiz-Lopez. Global environmental implications of atmospheric methane removal through chlorine-mediated chemistry-climate interactions. Nature Communications, DOI: 10.1038/s41467-023-39794-7