While other factors, including a sluggish U.S. economy and increasing energy efficiency, have contributed to the decline in carbon emissions from factories, automobiles and power plants, many experts believe the switch from coal to natural gas for electricity generation has been the biggest factor. Carbon-dioxide emissions account for nearly 84% of greenhouse-gas emissions, while methane—the main ingredient in natural gas—makes up 8.8%, according to a recent Environmental Protection Agency report.
Natural gas emits half as much carbon dioxide as coal when used to make electricity, though the calculation fails to take into account the release of methane from natural-gas wells and pipelines, which also contributes to climate change.
Last year, 30% of power in the U.S. came from burning natural gas, up from 19% in 2005, driven by drilling technologies that have unlocked large and inexpensive new supplies of the fuel.
The U.S. trend hasn't led to a global decline in carbon emissions, which increased 15% from 2005 China's rising reliance on coal to fuel economic growth jeopardizes progress toward what the IEA calls "a low-carbon future." But the U.S., which has decreased its carbon-dioxide output tonnage more than any other nation, demonstrates that market forces can have an impact on greenhouse gases even as politicians continue to disagree over what, if any, federal regulations are needed to force industries to reduce their emissions. (WSJ, 4/18/2013)