Reducing automobile activity helps reduce air pollution. But antagonistically, this also contributes to increasing the problematic concentration of methane as shown in a study published in the journal Nature.
Reducing automobile activity: a double-edged sword
Does reducing automobile activity reduce air pollution? Even if this does not magically make all pollutants disappear from the atmosphere, data like that of Airparif proved during the great confinement of 2020 that the sharp reduction in road traffic had a clear influence on the concentration of carbon dioxide. nitrogen (NOx). Counterintuitively, however, researchers noted an increase in the concentration of methane in the atmosphere in several places around the world where transport activity had significantly reduced that year.
A study published in the journal Nature by Professor Shushi Peng of Peking University helps us understand why. According to the study data, the concentration of nitrogen oxide has decreased in the atmosphere during periods of confinement. This reduction in the concentration of nitrogen oxide has contributed to increasing that of methane: emissions of nitrogen oxides lead to the presence in the air of “hydroxyl radicals” (OH), which notably neutralize the methane present. When these nitrogen oxide emissions decrease, there would be fewer hydroxyl radicals and therefore more methane.
The mysterious increase in methane in 2020
Researchers were surprised by a sharp increase in the concentration of methane (CH4, same molecule as natural gas) in the atmosphere in 2020, despite the confinements associated with the Covid-19 pandemic. The slowdown in economic activity has resulted in a drop in methane emissions linked to the fossil fuel industry.
In a study published in the journal Nature, led by Professor Shushi Peng of Peking University, an international team of scientists revealed the key to the enigma, which can be explained by two phenomena. The first factor is a lesser presence in 2020 of hydroxyl radicals (OH), mainly responsible for the elimination of methane in the atmosphere. These OH, present in infinitesimal quantities and with a lifespan of less than a second, are “the Pac-Man of the atmosphere: as soon as they see something, they eat it and they disappear,” explains the researcher. French Philippe Ciais.
Bad news for the climate
The second factor identified is linked to an increase in natural methane emissions from wetlands. Microorganisms present in swamps or peat bogs naturally produce this gas. These areas are “very sensitive to climate”, indicates Marielle Saunois, from the Climate and Environmental Sciences Laboratory (LSCE). “Microorganisms will produce more methane in warmer, more humid climates.” In 2020, wetter and warmer conditions in the high northern latitudes and in the tropics of the Northern Hemisphere therefore explain greater methane production.
These findings signal a possible “runaway” warming, which could in turn produce more harmful emissions, fueling a vicious cycle. The study also points to the paradoxical effect of the reduction in pollution. “When we reduce NOx emissions by around 20%, we can increase methane twice as quickly and that surprised us a lot,” remarks Philippe Ciais.
Methane: a major challenge in the fight against global warming
Programs to combat emissions therefore risk increasing methane in the future. “So if we want to meet the objectives of the Paris agreement we will have to act even faster and even stronger to reduce the sources of methane,” argues Philippe Ciais.
Methane is the subject of particular attention in the fight against climate change because, even if it has a much shorter lifespan in the atmosphere (around ten years) than that of CO2, its warming power is much higher: 28 times more over 100 years. This gas is responsible for about a third of global warming since the Industrial Revolution. Its emissions are mainly (60%) linked to human activity, on which it is therefore possible to act: fossil fuel industry, agriculture, livestock, waste, etc. The rest comes from wetlands.
Further research and future challenges
An enigma remains, because the concentration of methane continued to increase in 2021. But the researchers already have some leads: “it would seem, according to very preliminary results, that we still have a concern at the level of OH”, says Philippe Ciais. The phenomenon could be explained by the only partial resumption of air transport – whose role in the production of NOx at high altitude is very important – and by still low transport activity in the United States and India.
In summary, if reducing automobile activity helps to reduce air pollution, it also poses unexpected challenges for global warming. Efforts to balance NOx and methane emissions will need to be carefully calibrated to avoid unintended climate consequences.
https://www.sfsm.info/un-etre-vivant-qui-defie-les-lois-de-la-nature-decouvrez-lagence-qui-na-pas-besoin-doxygene-pour-survivre/
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