US CO2 Emissions Dive to 20-Year Low Cheap natural gas has made a huge difference By Rob Quinn, Newser Staff Posted Aug 17, 2012 2:44 AM CDT Updated Aug 17, 2012 3:31 AM CDT 14 comments Comments A crew works on a drilling rig at a well site for shale-based natural gas in Zelienople, Pennsylvania. (AP Photo/Keith Srakocic) (Newser) – America's carbon emissions have, amazingly, dropped to levels near where they would be in an alternate reality where President Al Gore signed the Kyoto Protocol. Emissions of the greenhouse gas are at their lowest in 20 years and government officials say the dramatic fall is thanks to cheap natural gas, which has caused a big switch away from coal, the AP reports. Coal was used to generate around half the electricity used in the US in 2005 but now generates only around a third, and the wholesale price of natural gas has gone from $7 or $8 a unit to around $3 over the last four years. The market-driven change, which has surprised climate scientists, is cause for "cautious optimism" about dealing with climate change, says the chief of Penn State's Earth System Science Center. It shows that "ultimately, people follow their wallets" on the issue, he says. But there is still plenty of cause for concern, environmental groups warn. The fracking responsible for the boom in cheap gas comes with its own environmental issues, and there's no guarantee that coal will stay more expensive than gas in the years to come.