Methane pollution has just reached new heights
After a sharp increase in the 1980s and 1990s, atmospheric methane has then stabilized. Growth resumed in 2007 and accelerated in recent years: the strongest increase ever occurred in 2020. This was not expected when world leaders signed the 2015 Paris Agreement. becoming the biggest discrepancy from the emission trajectories needed to reach the agreement's goal.
So what's behind the recent wave and is there a way to reverse it? About 600 million tons of methane are released into the atmosphere every year. Estimates suggest that two-fifths of these emissions come from natural sources, mainly rotting vegetation in swamps. The remaining three-fifths of emissions come from sources related to human activity.
The emissions of the fossil fuel industry produce well over 100 million tons per year and grew rapidly in 1980. Natural gas, which in the UK heats homes and generates about half of the electricity, is mainly methane.
Leakages in the gas industry are widespread in wells and pipelines and from distribution pipes under the streets and domestic boilers. The coal industry was responsible for up to a third of fossil fuel emissions between 2000 and 2017 through ventilation shafts in mines and during the transportation and crushing of coal for power plants.
L agriculture, which produces around 150 million tons per year, is the largest overall source. As well as urban landfills and sewage systems, they contribute about 70 million tons per year. Scientists can identify 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 decaying vegetation or in the stomach of cows, is relatively rich in carbon-12, while methane from fossil fuels and fires has relatively more carbon-13.
For two centuries, the rapid expansion of the gas, coal and oil industries has consistently resulted in atmospheric methane being richer in carbon- 13. Since 2007, this trend has reversed and the proportion of carbon-13 in atmospheric methane has decreased. Although fossil fuel emissions may still be on the rise, the surge in methane emissions is now primarily the result of faster-growing biogenic sources.
Global monitoring shows that in many years since 2007, the growth of methane in the atmosphere has been driven by sources in the tropics and subtropics. In some years, the high northern latitudes have also been important contributors. From tropical swamps in the Amazon, Nile and Congo basins to the tundra in Russia and swamps in Canada, wetlands emit around 200 million tons of methane per year. As global temperatures rise, the rate at which wetlands generate and decompose biomass increases and these environments release more methane.
Methane emissions accelerate climate change, and climate change causes the release of more methane - a positive feedback from warming that feeds more warming. Microbes in the stomachs of ruminant animals such as cattle, sheep, goats and camels are similar to wetland microbes. Indeed, the cows are walking in the wetlands. Ruminants produce nearly as much methane as fossil fuel emissions, about 115 million tons per year. Globally, around two-thirds of agricultural land is pasture for animals.
While landfill emissions have been reduced in many European countries, Western Europe emits a lot of methane from biodigesters that convert food and urban garden in fertilizers. In Africa and India, expanding cities are creating new landfills as rural areas burn large amounts of plant and grass waste, causing widespread air pollution, but there is little research on their emissions.
La short methane life means that reducing emissions quickly reduces the impact of the greenhouse. Gas leaks are obvious targets, both in wells and leaking road pipes. Ending the coal industry is an urgent global priority, not only to reduce methane but also CO2 and air pollution.
In the short term, the removal of methane from mine air ventilation coal and cattle barns can be done as easily as some pollutants are removed from car exhausts. Emissions from biodigesters will need tougher government regulation. Reducing emissions in tropical nations means ending the burning of crop waste. Landfills are likely to be rapidly growing sources of both methane and pollution, but emissions can be reduced by covering landfills with soil. Increasing agricultural emissions are linked to rapid human population growth and growing global demand for a diet rich in meat. Population growth has slowed by improving access to education for women and girls.
Methane hitting 1,900 ppb is a fire alarm. We cannot stop the natural emissions of wetlands. But man-made emissions can be reduced quickly. At COP26 in Glasgow - the most recent UN climate change summit in November 2021 - more than 100 nations signed the Global Methane Pledge, vowing to reduce methane emissions by 30% by 2030.
Getting started is simple: plug gas leaks, cover landfills, stop the burning of crop waste, and remove methane from coal mine ventilation. All of these actions will have wider benefits such as reducing air pollution, but large emitters, including China, India, Russia, Qatar and Australia, have not signed up.
