Robert Howarth

David R. Atkinson Professor of Ecology and Environmental Biology

Robert Howarth is a professor of ecology and evolutionary biology at Cornell University and an expert on the atmospheric implications of methane. While some researchers have concluded that cows and cattle are the cause of the increase, he says shale gas and shale oil are the most likely reasons behind the steep climb.

Howarth says: 

“Methane levels are at the highest levels they have been for hundreds of thousands of years. As with CO2, humans are the clear cause of the increase, and in fact human activity has increased methane levels to a greater extent (170 percent) than is the case for CO2 (45 percent).

“Several papers over the past 18 months have concluded that fossil fuels may not be cause of the latest surge in methane. However, there is very strong evidence that these papers are wrong. 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 shows that the increase in global methane emissions over the past decade has come mostly from the United States: 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.

“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.”