In a paper released Thursday, researchers from Cornell University firmly stood by an earlier claim that shale gas has a larger greenhouse gas (GHG) footprint than conventional gas and oil or coal, and thus would be an unsuitable bridge fuel.

“We restate the conclusion that shale gas emits far more methane than conventional gas and has a larger greenhouse gas footprint than either oil or coal,” said Cornell ecologist Robert W. Howarth, who spoke in a teleconference with reporters after the paper was released. “We stand by the conclusion of our [April] 2011 research: The large [GHG] footprint of shale gas undercuts the logic of its use as a bridging fuel over the coming decades, if the goal is to reduce global warming.”

Howarth and his team were responding to criticism of his initial report by another group of Cornell researchers and other research groups who said the study was “seriously flawed” in that it followed a process that “significantly overestimated” GHG emissions from natural gas production.

The natural gas industry already dominates methane emissions in the United States, Howarth told reporters. Methane from natural gas makes up 17% of total GHG emissions in the United States and he added that shale gas would increase that to 23% of the total national GHG inventory if it continues at its current development pace.

Howarth was joined by Cornell researchers Renee Santoro and Anthony Ingraffea, who published their findings in the academic journal Climate Change. Last April Howarth and his team concluded that methane leaked during shale natural gas drilling and production activities was higher than that seen from wells in conventional plays and a more serious threat to global warming than carbon dioxide (CO2) released from coal (see Shale Daily, April 13, 2011).

Research shows that the United States is reaching the “tipping point” with respect to global climate change over the next 15-20 years, Howarth said. “Shale gas is simply taking us in the wrong direction.”

Globally there are approximately 25,000 high-volume shale gas wells being developed, said Ingraffea. He estimated that there will be hundreds of thousands of shale gas wells planned in the United States alone, and perhaps more than one million worldwide over the next 20-30 years. Regulators and legislators have to “stop ignoring or incorrectly assessing what we now see as a very clear connection among shale gas development, greenhouse gas emissions and climate change,” he said.

Late last year rival researchers at Cornell published a paper that challenged Howarth and his team’s findings (see Shale Daily, Dec. 1, 2011).

In a paper published in Climate Change earlier this month, this separate Cornell team of researchers said Howarth’s analysis in the April 2011 report “is seriously flawed in that they significantly overestimate the fugitive emissions associated with unconventional gas extraction, undervalue the contribution of ‘green technologies’ to reducing those emissions to a level approaching that of conventional gas, based their comparison between gas and coal on heat rather than electricity generation (almost the sole use of coal), and assume [an unreasonable] time interval over which to compute the relative climate impact of gas compared to coal.”

According to the critical paper by Lawrence M Cathles III and other Cornell researchers, “high leakage rates, a short methane GWP [global warming potential], and comparison in terms of heat content are the inappropriate bases upon which Howarth et al. ground their claim that gas could be twice as bad as coal in its greenhouse impact. Using more reasonable leakage rates and bases of comparison, shale gas has a GHG footprint that is half and perhaps a third that of coal.”

Howarth’s report last year also was widely attacked by the oil and gas industry, as well as other independent researchers.

Subsequent studies conducted by the Worldwatch Institute and Deutsche Bank Climate Change Advisors; IHS Cambridge Energy Research Associates; Carnegie Mellon University; Wood Mackenzie; the U.S. Environmental Protection Agency; and the gas-friendly American Clean Skies Foundation criticized the Howarth study for overstating emissions and said natural gas has fewer GHG emissions than coal (see Shale Daily, Oct. 11, 2011; Aug. 25, 2011; Aug. 19, 2011; May 11, 2011; April 21, 2011).