The latest update to Carnegie Mellon University’s Power Sector Carbon Index (PSCI)— a quarterly report that tracks carbon dioxide (CO2) emissions and intensity from the U.S. power sector — shows that 2017 U.S. electricity generation CO2 emissions were 27 percent below 2005 levels, as the following chart from the report illustrates.

Not coincidentally, the report also shows that natural gas’ share of the total electricity generation mix increased 67 percent during that time (760 to 1,270 million megawatts), helping power plant CO2 emissions drop to their lowest levels since 1988. As the following chart from the report illustrates, natural gas’ net electricity generation share has jumped from 19 percent in 2005 to 32 percent last year, thanks largely to abundant and affordable natural gas supplies made possible by shale development.

As CMU acknowledged last year when it launched its PSCI report, a majority of the significant power sector CO2 reductions observed since 2005 can be attributed to increased natural gas use.

“The U.S. power sector has been getting cleaner and more efficient. CO2 emissions intensity from U.S. electricity generation decreased by 24% between 2005 and 2016 (from 1,324 lb CO2 per MWh to 1,005 lb CO2 per MWh – or 600 to 456 g CO2 per kWh). About 53% of this decrease is due to the shift in the mix of electricity generation from coal to natural gas.”

These trends continued in 2017, as natural gas enjoyed its second consecutive year as the top fuel source for electricity generation. Even though total electricity generation increased two percent in the fourth quarter of 2017 when compared to the fourth quarter of 2016, U.S. power plant emissions were down four percent from the same time frame in 2016, according to the report.

This can largely be attributed to the fact that natural gas generation increased four percent, 305 million megawatt hours (mmwh) year-over-year, more than twice as much hydro, wind and solar combined (147 mmwh).

The report also shows that power sector carbon intensity — which is total carbon emissions divided by total output — has declined 28 percent since 2005, prompting report co-director Ines Azevedo, a CMU associate professor of engineering and public policy, to state in a Youtube video accompanying the report that,

“Between 2005 and now, the carbon intensity of the electricity sector decreased by almost a quarter. This is really good news.”

The new CMU data echoes the U.S. Energy Information Administration’s (EIA) recent report that states significant declines in U.S. CO2 reductions achieved since 2005 can “mainly” be credited to increased natural gas use for electricity generation.

The EIA has previously reported that carbon reductions attributable to increased natural gas use between 2005 and 2016 were about 72 percent greater than what as saved by using so-called “non-carbon” energy sources, like renewables, as the following EIA chart shows.

The new CMU data is also just the latest example of how increased natural gas use — made possible by fracking — has enabled the United States to lead the industrialized world in carbon reductions while at the same time enjoying significant economic growth, a previously unheard of decoupling trend.