After a decade of blaming oil and gas drilling, turns out cows and rice are among primary culprits: NOAA

Recent increases in atmospheric methane are not because of fossil fuels after all, according to a recent release from the National Oceanic and Atmospheric Administration (NOAA).

After rising for almost two decades, atmospheric methane concentrations were essentially flat from 1999 to 2006.

This puzzled climate scientists, but then concentrations resumed growing in 2007, and they have risen steadily since. Initial explanations for the current rise mostly focused on oil and gas drilling, particularly blaming the U.S. shale boom.

NOAA Study: Agriculture and Wetlands Triggered Earth’s Methane Rise—Not Oil & Gas Operations

Source: NOAA

Isotope analysis rules out fossil fuels

However, recent analysis has cast doubt on that explanation. Methane from oil and gas production contains a relatively high amount of carbon-13, a rare isotope of carbon. Overall, carbon-13 makes up about 1.1% of all natural carbon on earth. If the recent increase in methane is due to leaking oil and gas wells, the proportion of carbon-13 in atmospheric methane would increase.

In reality, though, the opposite has occurred. Carbon-13 methane has actually been decreasing since 2007 worldwide, NOAA found.

NOAA Study: Agriculture and Wetlands Triggered Earth’s Methane Rise—Not Oil & Gas Operations

Source: NOAA

Carbon-13 drop rules out fossil fuel emissions, wildfires and biomass cooking fuels as methane instigators—blame falls on microbes in animal stomachs and underwater soils

The decreasing carbon-13 effectively rules out fossil fuel emissions, wildfires and biomass cook stoves as responsible for the post-2007 surge in methane. Instead, wetlands and agriculture seem to be to blame. Microbes in animal stomachs and underwater soils often emit methane instead of carbon dioxide.

In agriculture, cows and rice cultivation are primary sources of methane. Based on global agricultural statistics, however, production of cattle and rice has not grown enough in the past decade to explain the rise in methane. It seems likely that microbes in wetlands are responsible for the majority of the recent growth in methane concentrations.

Blame the rain

Emissions of methane from wetlands are exponentially higher in wet years than dry years. In the early 2000s, drier conditions were common, holding down wetland methane. Since 2007, though, wet years have been more common, making emissions from wetlands increase.

NOAA Study: Agriculture and Wetlands Triggered Earth’s Methane Rise—Not Oil & Gas Operations

Source: NOAA

Unfortunately, it may be difficult to deal with methane emissions from wetlands and agriculture. Reducing agricultural production may be difficult, especially in countries with growing populations. Reducing wetlands methane emissions may not be possible at all. Therefore, even though fossil fuel production is not to blame for the current growth in emissions, the oil and gas industry may be called on to help mitigate the recent rise.


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