A study showing that significant benefits for the ozone layer have already been achieved by the 1987 Montreal Protocol is published in Nature Communications this week. A much larger ozone depletion than that observed has been avoided by the protocol, with benefits for surface UV and climate.
Since the Montreal Protocol came into force and restricted the use of chlorine- and bromine-containing ozone depleting substances, atmospheric concentrations of these harmful substances peaked in 1993 and have subsequently declined. Martyn Chipperfield and colleagues now use a state-of-the-art 3D atmospheric chemistry model to investigate what would have happened to the ozone layer if the Montreal Protocol had not been implemented. They suggest that the Antarctic ozone hole would have grown in size by 40% by 2013 . Their model also suggests that had ozone-depleting substances continued to increase, stratospheric ozone loss would have become significantly worse in other parts of the globe. A very large Arctic ozone hole would have occurred under the meteorological conditions of 2011 and smaller Arctic ozone holes would have become a regular occurrence, allowing more UV radiation to reach the surface.
At mid-latitudes, where people are typically more sensitive to UV damage, the percentage changes in surface UV are important. In the most populated areas of Australia and New Zealand, which currently have the highest mortality rates from skin cancer, the model predicts that surface UV could have increased by 8-12%; and in Northern Europe, including the United Kingdom, increases would have exceeded 14% by 2013. While health effects are hard to quantify, the continued reduction in atmospheric emissions of chlorine and bromine should eventually translate into an increase in stratospheric ozone, reducing the incidence of skin cancer and preserving the temperature structure of the atmosphere, with important long-term consequences for circulation and climate.