WMO Scientific Assessment of Ozone Depletion: 2018

The WMO Scientific Assessment of Ozone Depletion provides Parties to the Montreal Protocol with updates on scientific developments relating to ozone depleting substances and the recovery of the stratospheric ozone layer. Together with Andreas Engel and a fantastic team of co-authors, I wrote Chapter 1: Update on Ozone-Depleting Substances (ODSs) and Other Gases of Interest to the Montreal Protocol. Our chapter summarised some really interesting developments that have occurred over the last four years: an increase in global CFC-11 emissions, the identification of new sources of carbon tetrachloride (which helps to reduce the “gap” in our understanding of its global budget), a slow-down in the growth of HCFCs, and many other things. A huge thanks to all the authors whose work we relied on (> 200 papers, mostly from the last four years), and the monitoring networks that make it possible to keep track of changes the concentrations of these important gases.

WMO Scientific Assessment of Ozone Depletion: 2018. Image courtesy: NOAA ESRL.

An unexpected rise in global CFC-11 emissions

The Montreal Protocol has been extremely successful in limiting the emissions of ozone depleting substances such as CFCs. As we’ve shown in previous papers, emissions and atmospheric abundances of these compounds have declined in recent decades. Since 2010, the Protocol mandates that there should be essentially no new production of CFCs for emissive use anywhere in the world. Therefore, our finding, published in Nature, that the rate at which CFC-11 is declining in the atmosphere has slowed since 2013 was surprising. Using atmospheric observations from the National Oceanic and Atmospheric Administration, we show that about 10,000 tonnes of this compound are being emitted to the atmosphere each year. This result has since been supported by data from the Advanced Global Atmospheric Gases Experiment. There have been some good summaries of the work in the New York Times, Washington Post, Guardian, etc. Since the paper came out, work by the Environmental Investigation Agency has shown that CFC-11 may still be produced in China. The next step for us is to use atmospheric observations to try to narrow down the location