The Montreal Protocol is widely regarded as the most successful international environmental treaty of all time, with substantial benefits to the stratospheric ozone layer and climate. However, recent work has shown that continued vigilance is needed. Emissions of the banned ozone depleting substance CFC-11 had increased from eastern China. The findings suggested the first major violation of the Montreal Protocol. Since publication, Chinese authorities have reported major enforcement activities to address the problem. However, the work highlighted several remaining scientific challenges that must be addressed to continue to support the Montreal Protocol and additionally, for climate, the Paris Agreement. Firstly, the magnitude of change in global emissions could not be reconciled with that inferred from eastern Asia, suggesting either that the global models could not accurately simulate year-to-year atmospheric trends, that the uncertainty estimates are insufficient, that there are as-yet-unidentified source regions of emissions elsewhere in the world, or some combination of each. Secondly, the work highlighted the critical need to accurately quantify emission magnitudes on global and regional (country to sub-continental) scales, not just for CFC-11, but for the more than 40 greenhouse gases (GHG) and ozone depleting substances (ODS) regulated under the Montreal Protocol and other agreements.
The project “GREEN GODS: Global and Regional Emissions Estimates of Non-CO2 Greenhouse gases and Ozone Depleting Substances” aims to use new models and statistical methodology to better quantify emissions of non-CO2 GHGs and ODS using atmospheric measurements and models of atmospheric transport.
This project has concluded with an increased knowledge of emissions of many greenhouse gases and ODSs, and an improved understanding of their drivers. A new, improved global model has been created, and made freely available, and is being implemented to quantify emissions of ODSs and greenhouse gases in a semi-operational manner. These emissions are anticipated to feed into the next Scientific Assessment of Ozone Depletion from the World Meteorological Organisation.
A particular highlight of the project has been work in determining that the emissions of many ODSs, for which production is banned for most uses under the Montreal Protocol, are increasing. This is thought to be primarily due to their use as feedstocks in the production of non-ODSs.
