Global environment impacts of enhanced chlorine emissions for methane removal through chemistry-climate interactions

Atmospheric methane is a potent greenhouse gas that is photochemically active. The addition of chlorine to the atmosphere has been proposed to mitigate global warming through methane reduction by increasing its chemical loss. However, the potential environmental impacts of such climate mitigation remain unexplored. We explore the possible effects of increasing reactive chlorine emissions on the methane budget, atmospheric composition and radiative forcing. Due to non-linear chemistry we found that achieving effective methane reduction require a minimum 3-fold increase in chlorine atoms compared to present-day levels. Our highest scenario, 50-fold present-day chlorine levels, led to a reduction of the surface temperature by 0.6°C in the year 2050. Beyond the direct effects on methane and temperature, our results show significant alterations in other climate forcers, particularly a large decrease in tropospheric ozone. This translates into a reduction in radiative forcing of a similar magnitude as of the methane removed. Additionally, the Antarctic stratosphere ozone burden during September and October was reduced by up to 40% with the highest chlorine addition. Consequently, the implementation of such strategies requires careful consideration of various factors, including the quantity and method of chlorine addition, as well as potential environmental impacts on air quality and ocean acidity.