Replacing coal with natural gas cuts the creation of greenhouse gases that cause global warming, a Cornell University researcher has concluded, rebutting the findings of colleagues at the university.
Lawrence M. Cathles, a professor in the department of earth and atmospheric sciences, released a paper that says even if high rates of natural gas are leaking out after hydraulic fracturing and during transport, gas will still provide a net benefit over time.
“The only thing that really counts is the amount of carbon dioxide you put in the atmosphere,” Cathles said in an interview today. Because gas releases less carbon dioxide than coal or oil when combusted, “the story is quite clear that we would be very well advised to substitute natural gas.”
The impact of natural gas on climate change has attracted attention as the spurt in production from hydraulic fracturing, or fracking, has pushed down prices and prompted power producers to shift from coal to gas. Utilities generated as much power from natural gas as coal in April, the first time natural gas equaled coal generation since the government started keeping those records, in 1973, the Energy Information Agency said July 6.
Cathles’ Cornell colleagues Robert Howarth and Anthony Ingraffea published an article last year that said leaks of methane from fracking, in which water, chemicals and sand are pumped into the ground to break apart rock and free gas, mean the use of natural gas could actually cause more global warming than coal.
The differences between the researchers hinge on two points: First, estimates of venting and leakages during gas production, and second, the time frame evaluated. Methane is a more potent greenhouse gas than carbon dioxide, but it’s removed from the atmosphere in less than 20 years, while carbon dioxide can persist for centuries.
Electricity production is the primary source of greenhouse- gas emissions in the U.S., according to the Environmental Protection Agency.
Howarth and Ingraffea used data from the EPA to develop its estimate of a leakage rate of up to 7.9 percent for methane, the key component of natural gas. Cathles says that estimate is off, basing his analysis on subsequent industry data and the fact that the release of that much natural gas would be both unhealthy and could pose a danger of explosion. Also, companies wouldn’t allow that much gas to escape freely, he said.
“It’s just an impossible number,” he said. Cathles’ estimates that it is more likely less than 2 percent of production.
Still, even if 10 percent of methane is being released, conversion to natural gas will still mean an almost 40 percent reduction in greenhouse gases beginning in a little more than a century and extending out for centuries to come.
Howarth and Ingraffea analyzed the impacts of natural gas compared with coal over the next two decades and one century.
“Compared to coal, the footprint of shale gas is at least 20 percent greater and perhaps more than twice as great on the 20-year horizon and is comparable when compared over 100 years,” they wrote in their paper published in the journal Climatic Change in April 2011.
Cathles said that 20 years is too short of a horizon to analyze the impact of greenhouse gases, which have been building up for more than a century. Over time, power production will need to shift to wind, solar and nuclear production.
“If we can encourage steps like the conversion to gas, we’ll buy ourselves time to convert,” he said.
Cathles’ paper was published in the journal Geochemistry, Geophysics, Geosystems on June 19. It was released to the public by Cornell’s public affairs office today.
Howarth and Ingraffea did not immediately respond to e-mail messages seeking comment on Cathles’ study.
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