Carnegie Mellon University just published an updated look at carbon emissions trends and data for the U.S. power sector that includes fourth-quarter and full-year 2017 information.

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Data: Carnegie Mellon University Power Sector Carbon Index; Chart: Axios Visuals

Why it matters: It gauges progress in wringing heat-trapping gases from what was, until recently, the largest source of U.S. carbon dioxide emissions (but has now fallen behind transportation).

The big picture: Carnegie Mellon's Costa Samaras tells Axios that total power-sector CO2 emissions last year fell to their lowest level since 1988, and that 2017 joined 2016 as the first two years that more total power came from gas than coal.

What the new data shows:

  • "Total annual rolling CO2 emissions were 1,770 million metric tonnes, which was 27% lower than in 2005," a summary notes.
  • The measure of emissions intensity — that is, pollution per unit of energy output — shows that emissions in Q4 were 952 pounds of CO2 per megawatt hour, which is 4% below Q4 of 2016 and 28% below 2005 levels.
  • Total power generation was up 2% in Q4 compared with a year earlier, though coal-fired output was down 6%.
  • A few more comparisons of Q4 2017 to the same stretch in 2016: Natural gas was up 4%, wind generation rose by 13% and solar went up by 30%.
  • To be sure: The renewables are growing from a small base. Wind and solar combined were 9% of U.S. generation in Q4.

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