CALIFORNIA, United States (Reuters) — Global methane emissions from agriculture and other sources have surged in recent years, threatening efforts to slow climate change, an international study has found.
Researchers led by French Laboratoire des Sciences du Climat et de l’Environnement (LSCE) reported that methane concentrations in the air began to surge around 2007 and grew precipitously in 2014 and 2015.
In that two-year period methane concentrations shot up by 10 or more parts per billion (ppb) annually, compared with an average annual increase of only 0.5 ppb during the early 2000s, according to the study released by the Global Carbon Project, which groups climate researchers.
Philippe Bousquet, co-author of the study and professor at Université de Versailles Saint Quentin, said the exact cause of the increase in methane emissions was still to be determined.
“After about 10 years of stagnation in the atmosphere methane is starting to increase again in 2007 and now we are observing a sustained increase since then and even accelerating since the last two years. So it’s a bit challenging to understand what is causing these increases in the atmosphere. It’s … methane increase in the atmosphere is linked to a balance between sources and things so there are changes in these sources and things and we are trying to understand what sources and things cause these changes,” Bousquet told Reuters after presenting his finds for the Global Carbon Project at the American Geophysical Union in San Francisco.
Methane is much less prevalent in the atmosphere than carbon dioxide (CO2) — the main man-made greenhouse gas — but is more potent because it traps 28 times more heat. The report did not say to what extent methane contributes to global warming.
“Methane is a very potent greenhouse gas, it’s 28 times more powerful as a greenhouse gas than CO2 over a 100 year horizon and it’s even 80 times more on an 80 year horizon. So this why of course we take a look at this very fast increase in methane, especially because CO2 emissions seem to be stagnating in the last years,” said Bousquet.
CO2 emissions are expected to remain flat for the third year in a row in 2016, thanks to falls in China, the Global Carbon Project said last month.
Bousquet warned that not tackling the rise in methane emissions could undermine efforts to control global warming.
“I think to stay below two degrees we have really to address this urgently and as methane has only a ten year life in the atmosphere, if we do something within ten years we see the effect. CO2 we need to wait, not hundreds, but tens of years, but with methane, in a few years, a decade, we have an effect so what we can do is, it’s already started, is to take all the waste and make biogas with this, you can burn this and emit CO2 but it’s less worse than emitting methane for example,” said Bousquet.
Bousquet said that while the reasons behind the methane surge are not well understood, the most likely sources are cattle ranching and rice farming. Cows expel large quantities of methane and the flooded soils of rice paddies are homes for microbes that produce the gas.
Figures from the United Nations’ Food and Agriculture Organization show that livestock operations worldwide expanded from producing 1.3 billion head of cattle in 1994 to nearly 1.5 billion in 2014, with a similar increase in rice cultivation in many Asian countries.
Bousquet said that methane can come from many different sources, including natural sources such as marshes and other wetlands, but about 60 percent comes from human activities, notably agriculture.
A smaller portion of the human contribution, about a third, comes from fossil fuel exploration, where methane can leak from oil and gas wells during drilling.
“The largest contributors individually are the natural wetlands, it’s about 30 percent of the emissions in the atmosphere and then we have … emissions from agriculture, waste and so on. But the largest one is the natural one,” said Bousquet.
