Quantifying the causes of the recent decrease in US CO2 emissions
Between 2007 and 2015 total annual US CO2 emissions decreased by 740 million tons (12%). An updated analysis shows that 35% of this decrease was caused by natural gas replacing coal in electricity generation, 30% by lower fuel consumption in the transportation sector, 28% by renewables replacing coal in electricity generation and 7% by other factors. The 515-million-ton (20%) decrease in electricity sector emissions between 2007 and 2015 was 50% attributable to natural gas replacing coal, 40% to renewables replacing coal and 10% to other factors. These estimates do not allow for the impacts of the 2008-9 global recession on emissions growth, which could have resulted in annual US CO2 emissions now being as much as a billion tons less than they otherwise would have been. This estimate is, however, speculative.
In previous posts here and here Euan Mearns and I made approximate estimates of how much of the recent decrease in US emissions was caused by what. I came up with this:
- Gas replacing coal in electricity generation: 40%
- Decrease in gm/mile vehicle CO2 emissions: 30%
- Growth in low-carbon renewables generation: 30%
And Euan, using a more detailed approach (and also including the impacts of the 2008-9 recession, which I ignored), came up with this:
- Gas replacing coal 55 Mtoe – 20%
- Fall in oil consumption owing to high price and recession 100 Mtoe – 36%
- Fall in fuel oil consumption 25 Mtoe – 9%
- Improved vehicle efficiency 26 Mtoe – 9.5%
- Aviation, shipping and unallocated oil savings 29 Mtoe – 10.5%
- [Biofuels 8.4 Mtoe]
- Growth in wind and solar 40 Mtoe – 15%
These estimates, particularly the “gas replacing coal” and the “growth in renewables” estimates, are a factor of two different. Other summaries to be found on the web range all the way from “fracking did it” to “the global recession did it”.
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