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Publishing in Nature Communications scientists present a new modelling study that investigates potential future climate warming and methane emission scenarios, and their possible effects on ozone precursor emissions and ozone pollution levels.
Prof. Bill Collins, Professor of Meteorology, University of Reading, said:
“This paper is slightly confusing since the headline result (that 3 degrees is worse for ozone pollution than 2 degrees) is due to assumed methane levels rather than temperature. However the impact of methane on ozone is something that is often overlooked and this study shows that reducing methane for climate purposes can have substantial pollution benefit too.
“The paper does show that in terms of the number of days of exceeding World Health Organisation limits, even two degrees of climate change will completely offset the expected benefits of air quality improvements over Europe. When the effects of methane are ignored the differences in ozone between a 2 degree and 3 degree warming are small.”
Prof. Paul Monks, Professor of Atmospheric Chemistry and Earth Observation, University of Leicester, said:
“The work deals with the so-called ‘climate penalty’ – the idea that future climate conditions will make it harder to achieve air quality goals. The paper shows that there could be significant increases of ground-level ozone, an air pollutant, across Europe in climate change scenarios. The paper squarely makes the challenge around joined up climate-change and air quality policy, recognising that that both affect each other. In particular in this case, the role of methane is associated with climate change but is also a precursor for the air pollutant ozone.”
Prof. David Stevenson, Professor of Atmospheric Chemistry Modelling, University of Edinburgh, said:
“In the 28 nations of the EU, 16,000 premature deaths each year are associated with ozone pollution1. Ozone pollution is not directly emitted but forms from chemical reactions in the sunlit atmosphere. Ozone’s precursors are oxides of nitrogen (NO and NO2, collectively known as NOx), carbon monoxide (CO) and hydrocarbons, including methane (CH4). All these gases are emitted by various human activities. In the last few decades European air pollution legislation has effectively regulated NOx, CO and many hydrocarbon emissions, leading to reductions in their concentrations that have benefitted air quality. However, methane is more difficult to control through just European emissions controls: it requires regulation at the global scale.
“This study reinforces previous findings that controlling methane at the global scale is crucial for keeping European ground level ozone pollution within acceptable limits. Methane oxidation in the lower atmosphere produces ozone. Methane levels have been rising strongly over the last decade, with a recent acceleration2. Methane has a ten year lifetime in the atmosphere, much longer than it takes to mix through the atmosphere, so emissions from anywhere on the Earth increase levels over Europe. Increases in global methane threaten to overwhelm European emissions control measures. To be effective, any agreement to limit methane emissions must be worldwide. The recent upturn in methane has been linked to increased exploitation of natural gas, but also the impacts of warming climate on natural methane sources from wetlands and permafrost. We don’t really need any more reasons to address climate change and control methane emissions, but one consequence of not doing so will be worsening ozone air quality.
“The study uses a respected regional model and the results seem perfectly sensible and reasonable. The major limitation is whether we really believe methane concentrations could follow the RCP8.5 scenario, which is eye-wateringly high – reaching 2740 ppbv in 2050. Current levels are about 1850 ppbv, with recent growth rates about 10 ppbv/year, so simply extrapolating that we’d reach about 2200 ppbv in 2050. To reach 2740 ppbv requires a growth rate of 27 ppbv/year, i.e. nearly 3 times the current rate.
“Even if the scenario used is a pessimistic one, the underlying message is clear: methane levels have a strong influence on future ozone air pollution, and if we don’t control methane globally, ozone air quality will deteriorate, potentially cutting short many people’s lives in Europe.”
* ‘A 3 °C global RCP8.5 emission trajectory cancels benefits of European emission reductions on air quality’ by A. Fortems-Cheiney et al. published in Nature Communications on Tuesday 25 July 2017.
Declared interests
Prof. Bill Collins: “No interests.”
Prof. Paul Monks: “I have nothing to declare as a direct interest with any of the authors, many of whom are known to me and one I have published a paper on ozone trends.”
Prof. David Stevenson: “I don’t think I have any conflicts of interest. I am a university academic who has been occasionally funded to work on ozone and related things.”