A study published by researchers and scientists with MIT, Stanford, and the National Renewable Energy Library was recently published that is essentially the first in depth look at US Methane emissions.
Why methane? The environmental issues with Natural Gas mainly come from the presence of methane - which is another green house gas, but 30 times more potent than the carbon dioxide we usually hear about. Approximately 1.5% of natural gas leaks during extraction, processing, transport, etc on its way to the consumer, so methane levels give us a bigger picture of the environmental impact of Nat Gas beyond carbon emissions.
Surprisingly- Hydraulic Fracturing or "Fracking" is not the problem. You read that correctly - the often hotly debated "fracking" process is not what's causing methane emissions to rise. So what is?
The study found that so called "super users" were responsible for the vast majority of the leaks (some processing plants, factories, etc). The good news is that in theory these repairs arent cost prohibitive, and are generally profitable for the site - at least in the long term - as they stand to lose less product in transmission.
The question then becomes - is this an issue that should be legislated on or not? Industry folks say they are already voluntarily correcting issues, and since they have a financial incentive in at least certain cases to do so, they don't need regulatory pressure to move the process forward. Environmental groups predictably say given the level of leaks still existant, volunteerism is not keeping pace with the level of repairs and upgrades required to address emission levels.
I wrote an article for Oil & Energy magazine's April issue on this topic, and the related discussion of whether its environmentally "friendly" to switch your fleet to Nat Gas in the long term. You can read that article here: Oil & Energy Online