Considered the second most important greenhouse gas (GHG), methane (CH₄) has received much less attention for decades than the better-known carbon dioxide (CO₂). However, the data are increasingly worrying: its emissions are breaking records, its link to human activities has increased and its concentration is already 2.6 times higher than in pre-industrial times, as shown by the latest assessment of the Global Carbon ProjectScientists warn that the global warming potential per molecule of CH₄ is up to 80 times greater than that of CO₂, and are calling for an immediate reduction in these emissions, which come mainly from the agricultural and livestock, energy and landfill management sectors.
The article, published in the specialized magazine Environmental Researchnow estimates that two-thirds of CH4 comes from anthropogenic activity. “Methane concentrations in the atmosphere are higher than ever because human activity continues to increase emissions,” summarises Pep Canadell, executive director of the Global Carbon Project (GCP) – a consortium of dozens of international scientists. “The most important sources come from ruminant livestock farming (cows, oxen, sheep), the fossil fuel industry (oil and natural gas), rice cultivation and organic waste that ends up in landfills,” he continues.
Added to this are natural causes: “In recent years we have had wetter conditions in the tropics due to the natural phenomenon of The Girlwhich has meant that there has been more rain than normal in tropical countries. And water-saturated soils also stimulate natural emissions,” says Canadell. Another key point is provided by Xavier Querol, an expert in atmospheric pollution at the Institute for Environmental Diagnosis and Water Studies (Instituto de Diagnóstico Ambiental y Estudios del Agua).IDAEA-CSIC): “Permafrost — the frozen soils of the Arctic and other areas — are melting due to climate change and turning into lakes or marshes that begin to emit methane, in turn driving climate change.”
The report shows that the concentration of methane in the atmosphere has reached a record rate of growth in the last five years since measurements began in the 1980s, and has already reached 1,931 parts per billion in January, a rate unprecedented in at least 800,000 years. In 1980 it was around 1,600 parts per billion. The researchers point out that this gas has contributed 0.5 °C of warming in the 2010s compared to the late 1800s, which represents two thirds of the warming caused by CO₂. “There is 200 times less concentration of CH₄ than CO₂, but only five times less greenhouse gas,” says Querol.
Agustín del Prado, expert in agri-food systems at the Basque Centre for Climate Change (BC3), explains: “The main greenhouse gas in terms of its impact on climate change has been carbon dioxide, and so it makes sense that the focus has been on this gas. But in recent years methane has acquired special relevance due to the urgency of reducing all greenhouse gases, the difficulties of decarbonising the planet at a sufficiently fast pace and because it is the second most important gas in terms of historical warming since pre-industrial times. In addition, with CO₂ we can focus the problem on fossil fuels, while with CH₄ the sources are very different.”
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There is a surprising knowledge gap: science cannot explain why, although emissions have increased continuously in recent decades, the concentration of methane in the atmosphere stagnated from 1999 to 2006. “It is surprising that we still have no answer to this phenomenon,” says Querol. “In any case, this gas can also increase or decrease due to oxidants, which accelerate its disappearance, although they then generate other pollutants that in turn generate ozone,” he adds. Whatever the case, it has not stopped increasing since 2007.
“Reducing methane emissions is the main way to be able to act on the climate in the short term,” says Luis Guanter, who heads a remote sensing group for this gas at the Universitat Politècnica de València (UPV). “This is because CH₄ has a shorter lifespan than CO₂, so if we were to reduce emissions in just 20 years the effects could be noticed and we would mitigate climate change, while the carbon dioxide emitted remains in the atmosphere for more than a century,” he adds.
Less gas leaks and additives for cows
The diagnosis is clear. What are the solutions? Canadell points out: “Methane leaks can reach 10% in some energy facilities, both from the extraction of fossil fuels and from pipelines that transport natural gas. The industry needs to solve this problem as soon as possible and reduce leaks to a minimum.”
David Yáñez, an expert in sustainable ruminant production at the Zaidín Experimental Station (EEZ-CSIC), offers another idea: “In Spain, where there is almost no extraction of fossil fuels, methane emissions from ruminants reach 40% of those generated by this gas and 6% of all greenhouse gases,” according to the official Emissions Inventory. “The European Commission has already approved the use of Bovaer, an additive —in whose development the CSIC has participated— that is added to the diet of cows and reduces their methane emissions by 30%.”
For now, only a few large companies are using it, which can get a return in advertising and advertise themselves as more sustainable, but not small livestock farmers, as they do not obtain an improvement in the performance of the animals. “In Denmark, the Government already has a roadmap to support the use of these additives with public money, and Belgium is also considering it. The challenge is to make it more widely used, because it helps to improve the balance of emissions in countries,” continues Yáñez.
As for agriculture, new methods must be applied to rice cultivation, as Canadell explains: “Instead of having the fields flooded throughout the production of this cereal, water is applied, then removed halfway through the season, the soil dries out a little, and then flooded again. This stoppage has very good results in reducing methane emissions by 20% or 30%. And other technologies are also being investigated.”
Meanwhile, Querol asks to focus on the large landfills: “The European Space Agency (ESA) has a satellite that measures methane; it published an article to show some black spots of emissions and there appeared many urban waste dumps, including the one in Valdemingómez. [Madrid]. What could be done? Canadell answers: “Try to reduce the amount of organic waste that ends up here to try to make compost, fertilizers or other by-products, or capture the methane and use it as biofuel in industrial processes that require heat.”
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