Natural short-lived halogens exert an indirect cooling effect on climate

Short-lived halogen species (SLH) are chlorine, bromine, and iodine compounds with a lifetime of less than six months in the atmosphere. These species are naturally emitted from the oceans, polar ice, the biosphere, and anthropogenic sources can also contribute to their atmospheric loading. Writing in Nature, the authors show that ocean-emitted SLH exert an indirect cooling effect on the climate system and that this natural cooling effect has been amplified since the beginning of the Industrial Era driven by anthropogenic activity. The results indicate that the net indirect cooling effect caused by SLH is the result of a trade-off between the highly non-linear chemical effects of halogens mainly on ozone and methane, with a minor contribution from aerosols and stratospheric water vapour. This interplay between SLH and the Earth's radiative balance is non-linear across past, present and future climates, and is determined by a combination of natural and anthropogenic emissions, climate variability and atmospheric chemistry.

Reference: Saiz-Lopez, A., Fernandez, R.P., Li, Q., et al. (2023). Natural short-lived halogens exert an indirect cooling effect on climate. Nature, 618(7967), 967-973. https://doi.org/10.1038/s41586-023-06119-z