Carbon dioxide emissions in the U.S. are at their lowest level in 20 years. It’s not because of wind or solar power.

...something amazing has happened: Carbon-dioxide emissions in the United States have dropped to their lowest level in 20 years. Estimating on the basis of data from the US Energy Information Agency from the first five months of 2012, this year’s expected CO2 emissions have declined by more than 800 million tons, or 14 percent from their peak in 2007.

The cause is an unprecedented switch to natural gas, which emits 45 percent less carbon per energy unit. The U.S. used to generate about half its electricity from coal, and roughly 20 percent from gas. Over the past five years, those numbers have changed, first slowly and now dramatically: In April of this year, coal’s share in power generation plummeted to just 32 percent, on par with gas.