A new study conducted by researchers at Carnegie Mellon University (CMU) reveals that carbon intensity from the U.S. power sector is down 30 percent since 2001. The report also notes that “declining generation from coal, and increased generation from natural gas and wind are the primary drivers for the CO2 intensity decrease.”

Carbon intensity is a key metric for analyzing emissions progress. While carbon emissions indicate the total amount of carbon dioxide produced, carbon intensity is defined as “the amount of carbon by weight emitted per unit of energy consumed.” Put another way, this report shows that energy efficiency has improved greatly in the U.S., due in part to an increased reliance on natural gas for electricity generation. As the U.S. Energy Information Administration (EIA) recently noted:

“Natural gas-fired units tend to be more energy efficient, requiring less energy content to produce a unit of electricity.”

Echoing the EIA’s assessment, the CMU report notes that “when lower-emitting electricity sources become a larger share of generation, the overall CO2 intensity of electricity decreases.” In the U.S., changes in intensity are proportional to total CO2 emissions, given relatively stagnant electricity demands.

The figure above shows the range of intensity decline was significant in each of the eight regions evaluated, with reductions ranging between 26 and 58 percent. Not coincidentally, the report notes, “One reason why all regions show at least some decline in intensity is that they all produced less electricity from coal and more electricity from natural gas and/or wind…”

This is largely attributable to the significant increases in use of natural gas for electricity generation. From 2001 through 2008, the electricity fuel and technology mix was consistent, with natural gas contributing about 20 percent of the total electricity. But the report notes that “2008 was at the start of a massive transformation caused by the drop in natural gas prices and increased generation from renewables.” It’s no coincidence that 2008 is right about the time the shale gas revolution began. In 2017, natural gas enjoyed its second consecutive year as the top fuel source for electricity generation.

The study also looked at carbon intensity on a state-by-state basis. Carbon intensity decreases were nearly unanimous across every state. Even states without any wind generation or Renewable Portfolio Standards (RPS) saw significant declines in their electricity CO2 intensity. From the report:

“Florida, Arkansas, Georgia, and Tennessee, which ended 2017 close to the national average, all increased generation from natural gas and decreased generation from coal. This coal-to-gas switch explain how states without RPS policies or large renewable resources have been able to reduce CO2 intensity. A shift to generation with natural gas can lower emissions…”

The new research out of CMU is the latest example how increased natural gas use – made possible by fracking – has enabled the U.S. to decrease both carbon intensity and carbon emissions, while maintaining industrial and economic growth.