Science | Pollution
The atmospheric concentration of this gas, which increases global warming, has nearly tripled since pre-industrial times.
The 2020 pandemic caused by Covid-19 led to the confinement of many countries and the stoppage of their economic activity. Planes were grounded, factories grounded their machines, workers were at home… These pandemic lockdowns led scientists to believe that anthropogenic emissions of methane, a potent greenhouse gas responsible for about 1/5 of global warming they would have been reduced. However, a new study, published Wednesday in the journal Nature, argues that the methane growth rate peaked in 2020, reaching the highest level since the World Data Center for Greenhouse Gases (WDCGG) began collecting data in 1984.
Once in the atmosphere, methane persists for an average of nine years, before decomposing thanks to the action of a natural oxidant called hydroxyl radical (OH), also called the 'detergent' of the atmosphere, due to its cleaning action of pollutants. , like methane. Still, small changes in methane concentration can have large effects on OH, and according to WDCGG data, the atmospheric methane concentration has nearly tripled from pre-industrial times to today, from 700 parts per thousand. million (PPB) to more than 1,900.
The main sources of anthropogenic methane emissions are: agricultural and livestock regions, fossil fuel extraction areas, landfills, fires, fresh water, permafrost and wetlands. According to the analyzes carried out, during the pandemic in most of them there was a slight decrease in methane emissions, compared to the emission sources obtained in 2019. Freshwater and permafrost remained unchanged, but in wetlands emissions they increased considerably, due to unusually hot and humid weather in the northern hemisphere, especially in the Arctic.
For their analysis, the researchers used two methane measurement methods, one bottom-up and one bottom-up. “For example, in the study we saw that bottom-up emissions from the fossil fuel sector, calculated from national activity data, such as coal, oil, and gas production, multiplied its emission factor. For its part, for emissions from fires and wetlands, we use satellite data," researcher Shushi Peng, one of the lead authors of the study, told this newspaper.
In spite of everything, it is difficult to know the true reality of this situation, due to calculation errors, voluntary or involuntary, by the sources involved in the emissions, such as the countries themselves or uncontrolled livestock and agricultural farms, among others. In fact, the use of satellites (GOSAT, Sentinel 5P...) to identify methane emitters, launched a few years ago, has shown an underestimation of emissions, especially in areas where fossil fuels are extracted, landfills and waste plants.
Another record in 2021
Thus, the objective for the future will be to ensure that the techniques for determining methane emissions into the atmosphere can obtain more reliable data from the complex sources of methane generation, purification and feedback, particularly in Central and South Asia, the Middle East, Africa and tropical South America, as recognized by the authors.
Although methane is not the greenhouse gas that we produce the most, it warms the atmosphere 25 times faster than other more abundant ones, such as carbon dioxide, which is why its unstoppable growth is alarming. The study's conclusions imply that methane emissions from wetlands are sensitive to a warmer climate and therefore could directly contribute to the greenhouse effect and global warming. “If warming increases methane emissions from wetlands, the concentration of methane in the atmosphere will increase, leading to further global warming. This is called positive feedback and it means that we will face a higher heating temperature than we expected before. That is why we must reduce emissions to mitigate global warming," explains Peng.
The reality is that the concentration of atmospheric methane increased again in 2021, reaching all-time highs, another aspect that this international team is already investigating. “My group is working on how methane emissions from wetlands could feed back into future warming this century. Filling the existing data gap is key to gaining a better understanding of this phenomenon,” says Peng.
Reactions to the study
In the opinion of Pep Canadell, executive director of the Global Carbon Project and lead researcher at the CSIRO Climate Science Center in Canberra (Australia), who has not been directly involved in the Nature research: "This study demonstrates the high level of alteration of the planet due to climate change, now with a possible new global warming feedback mechanism that few studies have previously shown to be very important: an increase in methane emissions due to increased precipitation in tropical swamps and warmer temperatures. high in cold boreal zones, including those with permafrost (frozen soils)“, he said in statements collected by the Science Media Center.
«This dependence of methane emissions on climatic characteristics (the higher the temperature and rainfall, the higher the emissions from wetlands) may be the origin of a positive feedback mechanism in the climate system that has not been considered up to now and which may give rise to to increase our estimates of future global warming. The result of this work shows us the need to better understand methane emissions from wetlands and their relationship with climatic conditions", added Ernesto Rodríguez Camino, Senior State Meteorologist and member of the Spanish Meteorological Association.