Three Cornell professors who published conflicting reports earlier this year on the amount of methane gas released into the environment by hydraulic fracturing, or fracking, are now embroiled in a debate over the accuracy of the others’ research.
Published in the scientific journal Climatic Change in April 2011, the first study –– co-authored by Prof. Robert Howarth, ecology and evolutionary biology, and Prof. Anthony Ingraffea, civil and environmental engineering –– claimed that the process of extracting natural gas from the earth ultimately releases a significant amount of methane into the atmosphere, where it acts as a greenhouse gas.
Prof. Lawrence Cathles, earth and atmospheric sciences, critiqued this conclusion in an Climatic Change article in January 2012. Cathles questioned some of the numbers used by Howarth and his colleagues.
Ingraffea said he measured potential methane leakages that could occur during the combined processes of extraction, purification and transportation to customers.
“We did what is called a ‘life cycle analysis,’ that is, you take not just the burning of the fuel –– whether it's coal, oil or natural gas –– but you take into account the production of greenhouse gases from the start of the investigation to produce coal or oil or natural gas all the way up to the end use,” Ingraffea said.
Using this more comprehensive analysis, Ingraffea determined that “the greenhouse gas footprint of natural gas ... is larger than the greenhouse gas footprint of coal and of oil.”
Howarth and Ingraffea’s paper estimated that, over the the lifetime of a shale gas well, between 3.6 percent and 7.9 percent of the methane released eventually becomes a greenhouse gas.
However, Cathles’ study cited a 2011 Environmental Protection Agency inventory report that he said indicated a much lower rate of leakage for wells — about 2.2 percent.
Cathles attributed this distinction to the fact that newer wells were being constructed with a process he called “green completion,” which would allow them to operate without venting or flaring methane. He cited an analysis of 1,578 shale gas wells by URS Engineering that found only 6.5 percent of wells were not constructed with this environmentally-friendly mechanism.
“What we’re talking about are wells that are going into place now, not the older wells — all but a few percent are green-completed; neither venting nor flaring, gas going right into a pipeline,” Cathles said.
However, Ingraffea cited EPA numbers from 2011 that indicated that most existing wells still vent or flare methane.
The two papers also differ on whether the potential environmental damage caused by the natural gas extraction process should be calculated by looking at a long-term or short-term time frame. Cathles said the effect of methane extraction might not be extremely detrimental to the environment over a 20-year time period.
“If we’re talking relatively long-range … and we think we are … even if methane were bad, we’d be better off using methane if it put less CO2 into the atmosphere,” he said. “If you do the transition over 20 years and you don’t have seven percent leaked, it’s a good deal.
Ingraffea countered that an increase in emissions over the short-term was not acceptable, as he feared it would irreversibly damage the global environment.
“Global climate change is the largest human health impact issue that will ever be addressed,” Ingraffea said. “My generation –– look what we did. We committed what I call generational greed … burning fossil fuel like there’s no tomorrow and guess what, there might not be.”
Prof. Bruce Lewenstein, communication said that conflicts like this often help both the scientific and public communities move toward more accurate facts.
“Science isn’t just the experiments described in textbooks; the real process of science is much messier,” Lewenstien said. “Individual scientists try different approaches, different methods, different ways of defining the problem. Reliable knowledge develops through the collective social interaction of responding to each others’ arguments.”