It is fair to say that we may literally owe our existence to methane. Although science has not yet been able to unravel how life first arose on this planet, and even the composition of the primordial atmosphere is still hotly debated, it is conceivable that methane was produced or consumed by some of the first terrestrial microorganisms, before breathable oxygen was available. According to current hypotheses, the ebbs and flows of this gaseous hydrocarbon, the main component of natural gas, were crucial in the evolution of the Earth’s climate, due to methane’s powerful greenhouse effect. However, applying on a planetary scale the maxim of Paracelsus that the dose makes the poison, the alarming recent rise in atmospheric methane is a recipe for a catastrophe on an Earth in the throes of a severe global warming crisis.
Source: NASA Scientific Visualization Studio
Although methane (CH4) is second on the list of greenhouse gases (GHGs) responsible for climate change, behind the more abundant and better known CO2, it is not because its effects are milder; in fact, it is 28 times more potent as a GHG than CO2 if its effect over a 100-year horizon is considered. This ability to warm the planet may have been crucial for the beginning of life on Earth, when the Sun was less bright than it is today. “Life began maybe about four billion years ago, and methanogenic archaea may have evolved very early after the split between the archaea and the bacteria,” geoscientist and GHG expert Euan Nisbet of Royal Holloway University of London tells OpenMind. “There was a powerful greenhouse effect in the air, likely from both CO2 and methane.”
Later, when the emergence of photosynthetic cyanobacteria began to populate the air with oxygen—the so-called Great Oxidation, about 2.4 billion years ago—the reaction of this gas with methane reduced levels of the hydrocarbon to produce CO2 and water; the result was a global cooling that buried the planet in ice for 300 million years. Methane has continued to play a key role in climate regulation, falling during the ice ages and rising in the interglacial periods.
The mysterious increase in anthropogenic methane
However, methane has a fundamental difference from CO2 that relegates it to second place among the climate’s enemies, and that is its short lifespan: while carbon dioxide remains in the atmosphere for centuries, methane lasts about 12 years (until it breaks down into water and more CO2). And given its mainly biological origin, this is why the episodic presence of this gas in the atmosphere of Mars is for scientists a possible indication of life on the neighbouring planet.
In our own world, the descendants of those first methanogenic microorganisms from the dawn of time have persisted to this day, especially in oxygen-deprived environments such as organic-rich sludge. “Nowadays they are widespread in landfills, cows’ stomachs (it mostly comes out of the front end on a cow, by the way: bovine eructation) and many other places where the oxygen has been consumed,” summarises Nisbet. Thus, there are significant natural sources of methane release into the atmosphere, such as wetlands—including rice paddies—but others are also due to human activity, such as livestock farming or resource extraction, transport (leaking pipelines) and the use of fossil fuels. According to the Global Carbon Project, about 40% of methane emissions are of natural origin—perhaps as much as 50%, according to other estimates—while humans contribute some 60%, mainly from livestock and agriculture (around 40% of the anthropogenic share), landfills and waste (around 20%) and fossil fuels (34%).
Alarm bells went off when data from the US National Oceanic and Atmospheric Administration’s (NOAA) Global Monitoring Lab (GML) revealed that atmospheric methane levels rose by 14.7 parts per billion (ppb) in 2020, the highest levels since 1983, when systematic recordkeeping began; however, as GML scientist Ed Dlugokenchy tells OpenMind, data correction suggests similar increases to those of 2007-08 and 2014-15. In December 2020, the global mean atmospheric level was 1,892.3 ppb, an increase of 6% since 2000. It is worth remembering that, despite the lull in human activity caused by the COVID-19 pandemic, CO2 levels have also continued to rise. But while the causes of the growth in CO2 emissions are well known, the forces behind the increase in methane are less well understood and much more elusive.
Wetlands and permafrost, two ecosystems to watch closely
The unusual growth in emissions in 2020 is “extremely worrying,” Nisbet says, given that it is “one of the highest growth increments in the observational record, even higher than in many years in the 1980s when the Soviet Union’s gas industry was extremely leaky.” According to Dlugokenchy, preliminary analyses of carbon isotopes in CH4, conducted at the University of Colorado’s Arctic and Alpine Research Institute, “suggest a strong contribution from increased emissions from a biological source, e.g., wetlands or agriculture.” The year 2020 was warm in the Arctic, the NOAA chemist notes, and the La Niña phenomenon intensifies moisture in the tropics. Thus, the 2020 weather may be responsible for an increase in wetland emissions, although “that is speculation; it will take time to study it carefully,” warns Dlugokenchy.
However, he adds, these anomalies in annual variability overlap with a longer-term trend, which is that, after a period of stabilisation between 2000 and 2006, “the atmospheric methane burden has been increasing since 2007, and the rate of increase may be increasing.” This was pointed out in 2020 by two studies published in Earth System Science Data and Environmental Research Letters by scientists from the Global Carbon Project. In their estimates of the global methane budget, the researchers found that emissions increased by 9% in 2008-2017 compared to the previous decade. The concentration of methane in the atmosphere is now about 2.6 times higher than in 1750, accounting for a quarter of global warming since then.
The authors explain that this sustained increase can be attributed mainly to human activity, fossil fuels and livestock. But as geoscientist Benjamin Poulter, a researcher at NASA’s Goddard Center and co-author of both studies, who is in charge of coordinating wetland methane emission estimates for the Global Carbon Project, tells OpenMind, the main concern is how warming itself can increase natural emissions: “The science community is very concerned about wetland methane and climate feedbacks,” says Poulter. “The more the climate warms, the more likely that permafrost thaws, making carbon available to microbes that produce methane or carbon dioxide—and in the tropics, warmer soils means more methane production.”
Objective: drastic reduction of emissions
However, Poulter adds that there is as yet no evidence of wetland involvement in the recent upswings, as there is no clear trend in satellite imagery of wetland growth or increased permafrost thaw since 2007, and the global increase is not restricted to polar latitudes or the tropics. “We really struggle with observations of methane to be able to understand what wetlands are doing to contribute to the atmospheric growth,” he says. No major methane emissions have been observed from Arctic regions, which contribute 4%, while 64% come from the tropics and 32% from the temperate belt. The increase is mainly attributed to agriculture, livestock and waste disposal in Africa and Asia (with the exception of China), while in China and North America fossil fuels are primarily responsible; only Europe has managed to reduce its methane emissions.
What is clear, however, is that the Arctic regions are particularly vulnerable to the ravages of climate change, and that carbon trapped in permafrost can be a ticking time bomb, whether it ends up producing biogenic methane, dissolved in rivers or released into the atmosphere in dry soils as CO2.
Against this background and at the current rate, the rise in global temperature could reach 3 to 4°C this century, far exceeding the Paris agreement’s targets of limiting warming to 1.5°C. “This is arguably the major deviation so far from the expectations of the Paris Agreement,” Nisbet notes. However, as the United Nations Environment Programme (UNEP) warns in its recent global methane assessment in collaboration with the Climate & Clean Air Coalition, there is an opportunity to reduce human-caused methane emissions by 45% in this decade, which due to the short lifetime of the gas could avoid nearly 0.3°C of global warming by 2045 and help meet the Paris targets. “One thing to keep in mind, a significant fraction of anthropogenic CH4 emissions come from fossil fuel use and agriculture, and there are cost-effective ways to reduce emissions, especially from the fossil fuel sector,” concludes Dlugokenchy.