(ORDO NEWS) — According to measurements by the National Oceanic and Atmospheric Administration (NOAA) in the US, methane recently reached levels of 1,900 parts per billion (ppb) in the Earth‘s atmosphere. This compares to about 700 ppb before the industrial revolution.
Methane is a powerful greenhouse gas but stays in the air for about nine years. Given the impact it has on other gases, its overall global warming impact since 1750 is about half that of CO2.
After a sharp increase in the 1980s and 1990s, the content of methane in the atmosphere has stabilized. Growth resumed in 2007 and has accelerated in recent years, with the sharpest increase on record occurring in 2020.This was not what world leaders expected when they signed the 2015 Paris Agreement. Methane becomes the biggest divergence from the emission trajectories needed to reach the goal of the agreement.
What is behind the recent spike in emissions, and is there a way to reverse it?
Where does methane come from
About 600 million metric tons of methane are released into the atmosphere each year. It is estimated that two-fifths of these emissions come from natural sources, mainly from rotting vegetation in swamps. The remaining three-fifths of emissions come from sources associated with human activities.
Emissions from fossil fuels are over 100 million metric tons per year and have grown rapidly in the 1980s. Natural gas, which in the UK heats homes and generates about half of electricity, is mostly methane.
Gas leaks are common at wells and pipelines, and from distribution pipes under streets and domestic boilers. The coal industry is responsible for emissions of up to a third of fossil fuels between 2000 and 2017 through ventilation shafts in mines and during transport and crushing of coal for power plants.
Agriculture, producing about 150 million metric tons per year, is the largest total source. So are the city’s landfills and sewer systems, yielding some 70 million metric tons per year.
Scientists can determine the sources of methane by studying the ratio of carbon-12 to carbon-13 in the atmosphere. These different forms of carbon – chemically similar but with different masses – are known as isotopes.
Biogenic methane produced by microbes in rotting vegetation or in the stomachs of cows is relatively rich in carbon-12, while methane from fossil fuels and fires contains comparatively more carbon-13.
For two centuries, the rapidly expanding gas, coal, and oil industries have steadily increased the amount of carbon-13 in atmospheric methane. Since 2007, this trend has reversed and the proportion of carbon-13 in atmospheric methane has decreased. While fossil fuel emissions may still be on the rise, the dramatic rise in methane emissions is now mainly the result of faster growth in biogenic sources.
Why are biogenic emissions rising?
Global monitoring shows that for many years, since 2007, the growth of methane in the atmosphere was due to sources in the tropics and subtropics. In some years, high northern latitudes also made a significant contribution.
From tropical swamps in the Amazon, Nile and Congo basins to tundra in Russia and reed swamps in Canada, wetlands emit about 200 million metric tons of methane per year. As global temperatures rise, the rate of biomass formation and decomposition in wetlands increases, and these environments emit more and more methane.
Methane emissions accelerate climate change, and climate change causes more methane to be released—a positive feedback loop where warming fuels more warming.
The microbes in the stomachs of ruminants such as cattle, sheep, goats and camels are similar to the microbes in swamps. Basically, cows are walking wetlands. Ruminants produce almost as much methane as fossil fuel emissions – approximately 115 million metric tons per year. Around two thirds of the world’s agricultural land is grazing for animals.
While emissions from landfills have declined in many European countries, in Western Europe a lot of methane is emitted from biodiggers that process urban food and garden waste into fertilizer. In Africa and India, growing cities are creating new landfills, and rural areas are burning huge amounts of crop and grass waste, causing widespread air pollution, but there is little research on their emissions.
Getting rid of methane
Methane’s short lifetime means that reducing emissions quickly reduces the greenhouse effect. Gas leaks are an obvious target, both in wells and leaky street pipes. Ending the coal industry is an urgent global priority, not only to reduce methane, but also to reduce CO2 emissions and air pollution.
In the short term, removing methane from the ventilation of coal mines and cowsheds can be done as easily as removing some pollutants from car exhaust. Emissions from biodiggers will require stricter government regulation.
Reducing emissions in tropical countries means stopping the burning of crop residues. Landfills are also likely to be rapidly growing sources of methane and pollution, but emissions can be reduced by covering landfills with soil.
Rising agricultural emissions are linked to rapid population growth and increased global demand for meat-rich foods. Population growth is slowing down due to improved access to education for women and girls.
A methane level exceeding 1,900 ppb is a fire alarm. We cannot stop the natural emissions of wetlands. But human-caused emissions can be reduced, and quickly. At COP26 in Glasgow – the last UN climate change summit in November 2021 – more than 100 countries signed the Global Methane Pledge, pledging to cut methane emissions by 30% by 2030.
Getting started is simple: plug gas leaks, cover landfills, stop burning crop waste, and remove methane from coal mine ventilation. All of these actions will have broader benefits, such as reduced air pollution, but major issuers including China, India, Russia, Qatar, and Australia have not joined. Countries that do not join the initiative end up hurting themselves and must sign a commitment. Conversation
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