Driving emissions reductions by developing scientific methods for the reporting of greenhouse gases and ozone depleting substances

Research Highlights

• The University of Bristol has provided evidence of poor practice and non-compliance with international climate change and ozone layer protection agreements
• This research has led directly to reductions in harmful emissions of greenhouse gases (GHGs) and ozone depleting substances, and to changes in reporting processes, including the identification of the first major breach of the Montreal Protocol on Substances that Deplete the Ozone Layer and a subsequent elimination of those activities from China following enforcement action
• Working at the national and international scale, the research has developed new measurements and models to improve the accuracy and credibility of emissions reporting, leading to new measurements and methods for reporting under the Paris Agreement and Kyoto Protocol used by governments in the UK and India and new accounting methods for carbon emissions under EU regulations on Land Use, Land Use Change and Forestry.

Responding to troubling emissions figures

Back in 2016, atmospheric scientists around the world were puzzled by a rise in CFC-11 emissions. This chlorofluorocarbon (CFC), once widely used in refrigerators and insulating foams, was supposedly out of use having been globally banned under the UN’s Montreal Protocol in 2010.

Signals from global atmospheric measurement networks were saying otherwise. Global concentrations of this notorious ozone-depleting substance (ODS) had been falling since around the late 1990s, but a jump in emissions started to appear in around 2013 in data from two independent networks: the National Oceanic and Atmospheric Administration (NOAA) and the Advanced Global Atmospheric Gases Experiment (AGAGE). These suggested that global concentrations of CFC-11 increased by around 11,000 to 17,000 tonnes per year during the period 2014–2017, as compared with 2008–2012. This shift could only mean that, in contravention of the Montreal Protocol, production had re-started. 

Tracing the source of CFC-11 emissions

Among the global network of scientists deliberating the CFC-11 trend data was the University of Bristol’s Atmospheric Chemistry Research Group. Having flagged the suspicious rise in global CFC-11 concentrations (later published in a 2018 Nature paper led by NOAA), the group set up a study in 2017 with a global team of collaborators from the AGAGE network to find the source of the emissions.

Existing NOAA and AGAGE data suggested that the emissions came from somewhere in eastern Asia. To obtain more precise data, the research team coupled high-frequency observations from two AGAGE monitoring stations with new modelling techniques.

The monitoring stations, in Gosan, South Korea, and Hateruma, Japan, showed 'spikes' in CFC-11 concentrations when plumes from neighbouring industrialised regions passed by. Further, these spikes had grown since 2013. The source of the unreported CFC-11 emissions was clearly close by.

Discovering the source of the emissions spike

Narrowing things down further, the researchers ran computer models that used weather data to simulate the movement of pollution plumes as they travel through the atmosphere.

Reporting their findings again in Nature (2019), the group showed that CFC-11 emissions in eastern mainland China were around 7,000 tonnes per year higher in 2014–2017 than in 2008–2012. While this finding did not explain the full increase in CFC-11 levels seen since 2013, at 40–60% of the global rise, it represented a very significant fraction.

Crucially, the researchers also showed that the increase occurred in a specific region, primarily the north-eastern provinces of Shandong and Hebei.

Swift government action shuts down illegal facilities - and emissions plummet

This event represented the first identification of a major breach of the Montreal Protocol, the historic international treaty credited with the recovery of the Antarctic ozone hole.

Delegates from China at the 31st Meeting of the Parties (MOP31) to the Montreal Protocol in 2019 outlined an array of law enforcement activities taken to clamp down on CFC-11 production since 2018. Chinese authorities had found and shut down numerous illegal production facilities, made prosecutions and seized ODSs, including CFC-11.

Further investigations by the research team indicated the likely impact of China’s swift actions, drawing again on the measurements from the AGAGE network and Bristol’s modelling techniques. In 2019, China’s CFC-11 emissions had dropped by around 10,000 tonnes per year since 2014–2017 (reported in Nature in 2021).

The timings of China’s enforcement actions and emission reductions, across 2018 and 2019, suggested that they were very likely triggered by the two publications co-authored by Bristol on the CFC-11 anomaly and source. It would be “quite coincidental” if this was not the case says Professor Matt Rigby, who led the Bristol team, given that – to the best of the team’s knowledge – there had previously been little information in the public domain concerning unreported ODS emissions.

The team are now examining a wider suite of ODSs, and plan to report further anomalies in emissions trends to the parties to the Montreal Protocol, should any be identified.