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Efficiency of short-lived halogens at influencing climate through depletion of stratospheric ozone


Halogens released from long-lived anthropogenic substances, such as chlorofluorocarbons, are the principal cause of recent depletion of stratospheric ozone, a greenhouse gas1,2,3. Recent observations show that very short-lived substances, with lifetimes generally under six months, are also an important source of stratospheric halogens4,5. Short-lived bromine substances are produced naturally by seaweed and phytoplankton, whereas short-lived chlorine substances are primarily anthropogenic. Here we used a chemical transport model to quantify the depletion of ozone in the lower stratosphere from short-lived halogen substances, and a radiative transfer model to quantify the radiative effects of that ozone depletion. According to our simulations, ozone loss from short-lived substances had a radiative effect nearly half that from long-lived halocarbons in 2011 and, since pre-industrial times, has contributed a total of about −0.02 W m−2 to global radiative forcing. We find natural short-lived bromine substances exert a 3.6 times larger ozone radiative effect than long-lived halocarbons, normalized by halogen content, and show atmospheric levels of dichloromethane, a short-lived chlorine substance not controlled by the Montreal Protocol, are rapidly increasing. We conclude that potential further significant increases in the atmospheric abundance of short-lived halogen substances, through changing natural processes6,7,8 or continued anthropogenic emissions9, could be important for future climate.

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Figure 1: Column ozone decrease due to VSLSs and RE.
Figure 2: Altitude-resolved ozone decrease due to VSLSs and long-lived ODSs.
Figure 3: Trend in VSLS-driven ozone loss and CH2Cl2 growth.


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We thank NERC for funding (TropHal project, NE/J02449X/1). Ground-based observations of CH2Cl2 are supported in part by NOAA’s Climate Program Office through its Atmospheric, Chemistry, Carbon Cycle and Climate Program. C. Siso, B. Hall, J. Elkins and B. Miller provided assistance in making and standardizing these measurements.

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R.H., M.P.C., W.F. and S.D. designed and performed all experiments using the TOMCAT model. A.R. performed experiments with the radiative transfer model. S.A.M. provided ground-based observations. All authors discussed the results and commented on the manuscript.

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Correspondence to R. Hossaini.

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The authors declare no competing financial interests.

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Hossaini, R., Chipperfield, M., Montzka, S. et al. Efficiency of short-lived halogens at influencing climate through depletion of stratospheric ozone. Nature Geosci 8, 186–190 (2015).

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