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A study published in Science Advances looks at reducing atmospheric sulphur and methane emissions from wetlands.
Dr Eiko Nemitz, environmental physicist, UK Centre for Ecology & Hydrology (UKCEH), said:
“The study highlights a likely important interaction between air pollution, greenhouse gases generated by human activity, and natural emissions. It shows that as sulphur emissions continue to decrease in response to a drive to improve air quality, as well as a side-effect of the decarbonisation of transport and industry to achieve net zero, this will likely increase natural methane emissions from wetlands.
“Sulphur emissions also contribute to the formation of aerosols (microscopic particles) that scatter light and lead to the formation of reflective clouds, thus exerting a cooling effect on the climate. The processes highlighted in this new paper provide a second mechanism by which control of sulphur emissions reduces climate cooling.
“Nevertheless, sulphur emissions continue to play a major role in poor air quality, causing damaging health impacts in many parts of the world, and there are fewer options to clean up the air than to reduce greenhouse gas emissions.
“In this context it is important to recognise that the reduction in sulphur emission and deposition will bring the wetlands closer to their original state, and the magnitude of their methane emissions closer to what they would have been without the human impact of elevated sulphur deposition.
“The impact of sulphur deposition on methane emission from wetlands has been suggested by a small number of studies on this subject for a couple of decades, but responses are variable. This paper upscales the impact and overcomes some of that variability by synthesising a larger number of studies and by exploring a range of response functions. Whilst the study seems robust, without access to the supplementary of the study, it is not possible to make a definite comment on the quality of the underlying data.”
Prof William Collins, Professor of Climate Processes, University of Reading, said:
“While we have long known that cleaning up air pollutants such as sulphur have a direct warming effect on climate, this study shows that cleaner air can indirectly warm climate by increasing natural emissions of methane. Methane is the second most important greenhouse gas and a large source of it is from natural wetlands.
“This study is the first to systematically analyse field measurements of wetland emissions under varying conditions of sulphur deposition. It shows that high levels of sulphur pollution up until the late 20th Century may have artificially supressed this source. As we clean up our industries and power production this natural emission of methane will rebound and further warm climate. The good news is that reducing climate change also reduces natural methane emissions, so further supporting the climate benefit of strong carbon reductions.”
Dr Adam Povey, Assistant Professor of Earth Observation, National Centre for Earth Observation, University of Leicester, said:
“This study provides an additional line of evidence that wetlands are highly important in understanding the climate. Wetlands rapidly respond to changes in weather and climate, and those changes feedback to the climate – in this case, amplifying warming. These interfaces between water, soil, and life are extremely difficult to understand due to the diversity of interlinked processes occurring. This paper provides decent evidence for the direction of this effect – that cleaner air increases natural methane emissions and this makes it more difficult to achieve net zero – and this is consistent with other lines of evidence. I would treat the precise numbers quoted with caution since (as described at the beginning of the ‘Discussion’ section) there are many confounding processes and substantial uncertainties around the conditions in wetlands that are not captured by this statistical analysis of existing experiments. The UK is in an excellent position to understand these processes due to our world-leading capacity to monitor atmospheric pollutants (such as sulphur) and to model the influence of life on the climate through the UK Earth System Model.”
‘The large role of declining atmospheric sulfate deposition and rising CO2 concentrations in stimulating future wetland CH4 emissions’ by Lu Shen et al. was published in Science Advances at 19:00 UK time on Wednesday 5 February 2025.
Declared interests
Dr Eiko Nemitz: “I have no conflicts of interest to declare.”
Prof William Collins: “Last year I was a member of a panel advising the NZ govt on its methane targets.”
Dr Adam Povey: “My funding is entirely from UKRI and ESA so I can’t think of any conflicts of interest.”