The Environmental Defense Fund will sue the U.S. Environmental Protection Agency over outdated methane emissions standards for the country's landfills.

Methane is a greenhouse gas 21 times more potent than carbon dioxide and contributes to smog and climate change. The methane generated by decomposing solid waste in landfills is the second largest source of human-caused methane in the U.S.

The gas, also produced in abundance on the nation's dairy farms, has gained popularity in recent years because it can be converted to electricity and generate carbon offset credits. The EPA is supposed to update landfill emissions standards every eight years but hasn't done so in 12 years, EDF said in a statement Thursday.

"Capturing the waste gas leaking from the nation's landfills and converting it to a local source of energy is a trifecta for the nation's economy, environment and energy security," Vickie Patton, EDF's deputy general counsel, said in a statement. "Converting methane pollution to a homegrown energy source is a common sense solution to address global warming and protect our kids' health while boosting the economy."