Over the last two decades, the rise in natural gas extraction has resulted in a dramatic increase in methane emissions in the United States, Canada and elsewhere.

Though some have suggested small leaks at hundreds of extraction points add up to explain the rapid rise methane pollution, new research shows a handful of major producers are responsible for the majority of emitted methane in the United States.

Researchers call these leaking gas wells "super emitters."

"We're finding that when it comes to natural gas leaks, a 50/5 rule applies: That is, the largest 5 percent of leaks are typically responsible for more than 50 percent of the total volume of leakage," Adam Brandt, an assistant professor of energy resources engineering at Stanford University, explained in a news release.

Brandt is the author of a new study on super emitters, published this week in the journal Environmental Science & Technology.

The volume of emitted methane pales in comparison to the amount of CO2 released into the atmosphere each year, but climate scientists are beginning to pay closer attention to the full array of greenhouse gases. Methane's greenhouse gas effect -- the process by which a pollutant encourages global warming -- is 30 orders of magnitude more severe than carbon dioxide.

Climate scientists estimate as much as 25 percent of man-made global warming is caused by methane emissions.

Despite its role in climate change, methane has been hailed as an ideal transitional fuel -- bridging the gap between dirtier fossil fuels and alternative energy sources.

To gain a better understanding of where methane emissions are coming from in the United States, Brandt and his Stanford colleagues surveyed data from previous methane leak studies using a statistical analysis technique called extreme value theory.

"Extreme value theory has been used to study everything from major flood events to crop losses brought on by drought and stock market crashes," Brandt said. "In all of these cases, infrequent events really drive a lot of decision-making and expenditure or have big economic consequences. We are the first to apply this technique in a formal and rigorous way to natural gas leaks."

The results of their survey suggest a handful of leaks are responsible for between 40 and 90 percent of all emitted methane in the United States.

Researchers say their findings offer good news. Finding a way to slow a few major leaks is much easier than plugging hundreds or thousands of smaller leaks.

"If companies can identify and fix the leaks in a small number of top emitters, that will go a long way toward reducing methane emissions in the U.S.," concluded Brandt.