While natural gas often is touted as a bridge to a clean energy future, new figures released by the government portray production of the fuel as a growing source of greenhouse gas emissions.

The decline in emissions of other gases is making headlines and sure to energize arguments against climate change regulation. But within the report are figures suggesting a rising star among contributors to global warming: methane, a key component of natural gas.

While carbon dioxide is still far more prevalent, methane traps heat in the atmosphere 20 times as effectively.

The data released Monday by the Environmental Protection Agency in its latest "greenhouse gas inventory" add a new element to a debate already raging over natural gas extraction in the U.S. Hydraulic fracturing, also known as “fracking,” involves injecting a chemical-laced fluid into the earth to free up gas deposits.

EPA’s assessment of greenhouse gases contributing to climate change also comes as the U.S. Supreme Court heard arguments today on whether citizens and state officials can file “public nuisance” lawsuits to force utilities to curb pollution. The Obama administration, taking sides with American Electric Power Co., Xcel Energy Inc., Duke Energy Corp. and Southern Co., argues the EPA already is taking steps against climate change.

The EPA inventory shows overall greenhouse gas emissions falling by about 6 percent in 2009 to their lowest level since 1995, a finding that is being widely interpreted as an environmentally positive side to the recession. Economic slowdowns tend to lead to lower energy consumption.

But methane emissions related to natural gas extraction, processing, storage and distribution increased by about 4 percent, the report shows. The EPA attributes its higher methane numbers primarily to increased production from natural gas wells.

The risks of hydraulic fracturing have been drawing increased scrutiny from the press and from Congress. A report released by House Democrats last week found that the 14 leading oil and gas service companies used more than 780 million gallons of fluids containing potentially harmful chemicals while fracking between 2005 and 2009. These fluids contained 29 chemicals, such as benzene, that have been classified as known or possible human carcinogens, the report found.

The American Gas Association, a trade group, says that natural gas is a “clean and efficient fuel from an environmental perspective” and that its attributes are “particularly noteworthy with respect to climate change.”

Paul Wilkinson, the industry group’s vice president for policy analysis, said today that the new EPA methane numbers do nothing to change that image. He also questioned the EPA’s methods of estimating emissions.

Methane emissions from all segments of the industry except production have gone down since 1990, Wilkinson said, in part because of voluntary programs. Increases in methane releases during production may be attributable to a “greater reliance on tighter formations of natural gas” that require fracking, he said. However, Wilkinson said, “We believe the EPA method of estimating emissions from fracking is still under some question. They’ve used a new methodology that’s been questioned very strenuously” by producers.

The American Petroleum Institute, in a letter to the EPA last month, complained about the way the agency measures methane. It expressed concerns that the new methods would result in “artificially inflated” numbers that fail to account for “significant emission reduction and emission controls” underway in natural gas operations.

EPA officials were unavailable for comment.

Even if methane emissions did increase 4 percent in 2009, as the EPA reported, natural gas remains an appealing alternative to coal, Wilkinson said. “When you look at the total picture, from the wellhead to combustion natural gas gives off dramatically less CO2 than coal,” he said. “These new numbers, if they hold up, would bring down the gas advantage a little bit until we get new [methane-control] technologies in place, but in no way would they change the overall picture.”

David Hawkins, director of the climate program at the Natural Resources Defense Council, said the EPA report highlights the need for more precise measurement of methane releases during natural gas production and “rules that require the capture of these large amounts of emissions” to prevent their release into the atmosphere.

“We’re going to be relying on gas — shale gas, in particular — for a significant amount of our domestic energy consumption,” said Hawkins. “We can’t do it cowboy style. We’ve got to have a housebroken industry — and that means measure, report and capture.”

Hawkins added that the industry has “no business complaining about inaccurate [EPA] numbers” when it has resisted rules that would require more accurate reporting. Saying natural gas is superior to coal in terms of greenhouse gas emissions, he added, misses the point.

“It’s not a good enough sales pitch for the industry to say natural gas is not as bad as coal. The atmosphere cares about the total amount of greenhouse gases going into the air. It doesn’t care whether one fuel is better or worse than some other fuel. Sloppy gas production and inefficient gas use put a lot more greenhouse gas in the air than is necessary.”

A Cornell University study released earlier this month — and criticized by the natural gas industry — suggests that natural gas extracted through fracking may have a larger carbon footprint than coal. Methane emissions are also higher for gas extracted through fracking than through conventional methods, the study found.

While the industry has argued that natural gas is clean and efficient, the Cornell study says coal and gas have similar effects over time. Other studies have reached similar conclusions.