Reducing the levels of sulphur in the atmosphere might unexpectedly raise the natural emission of methane from wetlands like peatlands and swamps, according to new research. This could lead to an additional release of 20-34 million tons of methane annually from these natural sources, indicating that the current goals for cutting human-made methane emissions should be more rigorous than those outlined in the Global Methane Pledge.
A new study indicates that lowering sulphur in the air might unintentionally boost natural methane emissions from wetlands, including peatlands and swamps.
Recent findings published in the journal Science Advances reveal that as global sulphur emissions decline due to clean air initiatives, combined with the warming effects and fertilization from carbon dioxide emissions, wetland methane production increases. This ultimately leads to higher emissions.
If wetlands start emitting an additional 20-34 million tonnes of methane each year, it suggests we need to strengthen the goals for reducing human-related emissions beyond what is currently specified in the Global Methane Pledge.
Methane is one of the most effective greenhouse gases at capturing heat in the atmosphere and is emitted from wetlands worldwide. Sulphur, in the form of sulphate, plays a distinct role in natural wetlands that curtails methane emissions, while carbon dioxide enhances methane production by stimulating plant growth that feeds methane-producing microorganisms.
Professor Vincent Gauci from the University of Birmingham, a senior author of the study, remarked:
“Well-intentioned policies aimed at lowering atmospheric sulphur seem to have the unintended effect of removing the sulphur ‘cap’ on wetland methane production. Combined with rising CO2 levels, this results in a significant increase in emissions.
“How has this happened? Essentially, sulphur creates conditions that allow one group of bacteria to dominate over another group that produces methane when they compete for limited food resources in wetlands. The acid rain caused by sulphur pollution over the past century had been effective enough to decrease wetland methane emissions by as much as 8%.”
“Now that clean air initiatives are in place, the unfortunate result of reducing sulphur deposition—though beneficial for ecosystems—is that we’ll need to put in much more effort to remain within the climate safety limits established by the Paris agreement.”
At COP26 in Glasgow, over 150 countries committed to the Global Methane Pledge, aiming to reduce human-caused methane emissions by 30% from a 2020 baseline by the year 2030.
This study adds to the evidence that decreasing atmospheric sulphur is contributing to faster-than-expected global warming. In 2020, regulations began to limit shipping pollution, which involved cutting down on sulphur dioxide and fine particles detrimental to health. This decrease in atmospheric sulphur over the oceans has been linked to greater warming than anticipated, a phenomenon referred to as ‘termination shock.’
Lead author Lu Shen from Peking University stated:
“Our research highlights the complexities of the climate system. The intricate biogeochemical interactions have not been sufficiently included in previous forecasts of future methane emissions. This study demonstrates the importance of accounting for these feedback mechanisms to accurately understand the future trajectory of this significant greenhouse gas.”
