Concentrations of carbon dioxide in the atmosphere surged at a record-breaking speed in 2016 to the highest level in 800,000 years, according to the World Meteorological Organization's "Greenhouse Gas Bulletin," which noted that the abrupt changes in the atmosphere witnessed in the past 70 years are without precedent, Cornell University pointed out.
Robert Howarth, Cornell professor of ecology and evolutionary biology and an expert on the atmospheric implications of methane, said while some researchers have concluded that cattle are the cause of the increase, shale gas and shale oil are most likely the reasons behind the steep climb.
“Methane levels are at the highest levels they have been for hundreds of thousands of years. As with carbon dioxide, humans are the clear cause of the increase, and in fact, human activity has increased methane levels to a greater extent (170%) than is the case for carbon dioxide (45%)," Howarth said.
“Several papers over the past 18 months have concluded that fossil fuels may not be the cause of the latest surge in methane. However, there is very strong evidence that these papers are wrong," Howarth said. "Several of the papers have concluded that an increase in emissions from cows and cattle is the cause. This conclusion conflicts strongly with the satellite data, which show that the increase in global methane emissions over the past decade has come mostly from the U.S.; numbers of cows and cattle have decreased in the U.S. over this decade, and so this cannot be the cause.
“By far, the most likely cause of the increase, in my opinion, is from shale gas and shale oil, as the increase in emissions from the U.S. indicated by the satellite data coincides closely in time with the shale gas revolution. No other major change in activities over this time period in the U.S. makes any real sense," he emphasized.
“Note that the papers indicating that cows are the culprit are basing their conclusions on the stable carbon (C13) isotopic composition in the atmosphere, but they have all missed some fundamental literature that shows that this value for methane from shale gas sometimes looks more like methane from cows than it does methane from conventional natural gas. That is, they may have made a fundamental flaw,” Howarth concluded.