Australia: The Land Where Time Began

A biography of the Australian continent 

Short-Lived Halogens – Efficiency at Influencing Climate Through Stratospheric Ozone Depletion

The principal cause of recent depletion of stratospheric ozone, that is a greenhouse gas, are halogens released from anthropogenic substances that are long-lived, such as chlorofluorocarbons (Myhre et al., 2013; Riese et al., 2012; Montzka & Reimann, 2011). It has been shown by recent observations that other important sources of stratospheric halogens are very short-lived substances, generally with lifetimes of less than 6 months (Sturges et al., 2000; Laube et al., 2008). Seaweed and phytoplankton produce naturally short-lived bromine substances, whereas short-lived chlorine substances are primarily of anthropogenic origin. In this study Hossaini et al. used a chemical transport model to quantify the ozone depletion in the lower atmosphere from short-lived halogen substances, and to quantify radiative effects of that ozone depletion they used a radiative transfer model. According to their simulations the loss of ozone from short-lived substances had a radiative effect in 2011 that was almost half that from halocarbons that were long-lived and, has contributed a total of about -0.02 W m^-2 to global radiative forcing since pre-industrial times. It was shown by their findings that natural short-lived bromine substances exert a 3.6 times larger ozone radiative effect than long-lived halocarbons, normalised by the content of halogen, and that atmospheric levels of dichloromethane, that is a short-lived chlorine substance that is not controlled by the Montreal Protocol, are increasing rapidly. They concluded that potential further significant increases in the abundance in the atmosphere of short-lived halogen substances, either through changing natural processes (Dessens, Zeng, Warwick & Pyle, 2009; Hossaini et al., 2012; Hepach et al., 2014) or the continuation of anthropogenic emissions (Leedham et al., 2013), could be of importance for the climate of the future.

Sources & Further reading

Hossaini, R., M. P. Chipperfield, S. A. Montzka, A. Rap, S. Dhomse and W. Feng (2015). "Efficiency of short-lived halogens at influencing climate through depletion of stratospheric ozone." Nature Geosci 8(3): 186-190.