Methane, the primary component of natural gas and among the more potent greenhouse gases, has far more of an effect on climate change than carbon dioxide. But determining the factor that should be applied to measure its relative warming affect is still being debated.
To crunch its numbers, the EPA calculated the average concentration of methane in the atmosphere over a 100-year period and determined that over that period methane is 21 times more potent than carbon dioxide. Using that equation, a ton of methane emissions is the equivalent of 21 tons of carbon dioxide.
But some scientists argue that the impact of methane gas should be calculated over a shorter time period, because methane degrades quickly, and because gas drilling releases large quantities of methane into the atmosphere all at once, likely concentrating and amplifying the effect.
Robert Howarth, an environmental biology professor at Cornell University, used research from the United Nations to calculate that if methane's potency were considered over 20 years rather than 100 years, it would be 72 times as powerful as carbon dioxide in terms of its warming potential.
Figured that way, the climate effect of methane from natural gas would quickly outpace the climate effect of carbon dioxide from burning coal. Howarth's research is incomplete and has been criticized because at first he failed to figure in methane emissions from coal mining. But he said that after correcting his error, the emissions from coal barely changed, and the data still showed that the intensity of methane could erase the advantages of using natural gas.
"Even small leakages of natural gas to the atmosphere have very large consequences," Howarth wrote in a March memorandum , which he says is a precursor to a more thorough study that could begin to scientifically answer these questions. "When the total emissions of greenhouse gases are considered … natural gas and coal from mountaintop removal probably have similar releases, and in fact natural gas may be worse in terms of consequences on global warming."
Howarth says his latest calculations show that the type of shale gas drilling taking place in parts of Texas, New York and Pennsylvania leads to particularly high emissions and would likely be just as dirty as coal.
Environmental groups say factual data on how much methane is emitted from gas fields—and what the warming affect of that methane is—should be locked down before major policy decisions are made to shift the nation toward more reliance on gas.
"You can't just assume away some of these sources as de minimus," said Tom Singer, a senior policy analyst for the Natural Resources Defense Council who focuses on emissions reporting in New Mexico. "You need to get a handle on them before you can make a determination."
Less Pollution Means More Profit
The EPA tracks fugitive and vented methane emissions through a program called Natural Gas STAR and then works to get drilling companies to save money by stanching their leaks and selling the gas they capture for profit. It was a discrepancy in the Gas STAR data that prompted the EPA to sharply revise the government's greenhouse gas statistics late last year.
According to Gas STAR's most recent figures, at least 1.6 percent of all the natural gas produced in the United States each year, about 475 billion cubic feet, is assumed to be leaked or vented during production. But those numbers were reported before the EPA adjusted its greenhouse gas estimates, and they are expected to rise when the new estimates are plugged into the calculation. If companies could capture even the gas leaked in Gas STAR's current estimates, it would be worth $2.1 billion a year at today's prices and would cut the nation's emissions by more than 2 percent right off the bat. Several studies show that maintaining and installing equipment to capture the emissions pays for itself within 24 months.