Recent increases in dichloromethane, an ozone-depleting substance, could delay the recovery of Antarctic ozone by 5-30 years, depending on the emissions scenario. The findings, published in Nature Communications, suggest that previously ignored chemicals may now be contributing to ozone depletion and should be considered to improve future ozone predictions.
Long-lived, human-produced chlorine species, such as CFCs, led to depletion of the stratospheric ozone layer in the 1980s, most drastically seen in the Antarctic. After introduction of the UN Montreal protocol in 1987, which regulated emissions of ozone-depleting substances, stratospheric ozone began to recover; the Antarctic ozone hole is currently projected to return to pre-1980 levels in the middle to latter half of this century. However, atmospheric concentrations of dichloromethane - a short-lived, ozone-depleting substance not regulated by the Montreal Protocol - have risen in recent years and could be contributing to ozone loss.
Ryan Hossaini and colleagues use observations and simulations with a global chemical transport model to examine the sensitivity of future stratospheric chlorine and ozone levels to sustained dichloromethane growth. Their projections show that continued dichloromethane increases at the average trend observed from 2004-2014 would delay ozone recovery over Antarctica by 30 years. If dichloromethane concentrations stay at current levels, the delay in recovery would be only 5 years.
Although the future trajectory of dichloromethane is uncertain, without any regulations on emissions, it is likely concentrations will fall somewhere in between the ranges presented here. Because ozone changes in the lower stratosphere alter the amount of solar radiation reaching the Earth, particularly in the Southern Hemisphere, this potential delay should be considered in climate projections.