Has switching to gas helped in reducing CO2 emissions?

We looked at 

The CO2 budget - Let's talk numbers

 in the first part of this series. The second article, No wonder gas turbines are selling at record levels, was about

 the current competitive positioning. This article analyses whether switching to gas has helped reduce CO2 emissions.

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You may recall all the hoopla surrounding the reduction in the U.S. CO

₂

emissions in 2013, coincident with new-found shale gas resources.  We had turned the corner on CO

₂

emissions…a true eureka moment!

This is what the U.S. Energy Information Agency published at the time. The 2416Mt and the 2053Mt values still exist in EIA’s May 2015 Analysis of the Impacts of the Clean Power Plan.

Note: million metric tonnes (Mt) is sometimes abbreviated as MMmt as in the graphic above.

On July 21, 2015, Nature Communications published a fascinating analysis of U.S. CO₂ emissions during same 1997-2013 period. The study was led by University of Maryland’s Klaus Hubacek in cooperation with Steven Davis, UC Irvine; Kuishuang Feng and Laixiang Sun.

Here is the graphic that they published, summarizing their findings. Fuel mix is the orange bar:

A few of their conclusions:

“Commentators in the CO₂ scientific community and media have linked the two trends, celebrating the climate benefits of the gas boom…..

Recently, the Third National Climate Assessment of  the  United  States Global Change Research Program also adopted this conclusion, stating that the decrease in US CO₂ emissions was ‘largely due to a shift from coal to less CO₂-intensive natural gas for electricity production’. 

Yet,  despite  potentially  significant implications for US climate and energy policy, there has been no quantitative analysis of whether the gas boom and changes in the fuel mix of the power sector are indeed driving the decrease in US CO₂ emissions…..

….We conclude that substitution of gas for coal has had a relatively minor role in the emissions reduction of US CO₂ emissions since 2007.

…. The large decrease (9.9%) in US CO₂ emissions between 2007 and 2009 was primarily the result of the economic recession…

……the modest effect of changes in the fuel mix of the energy sector on emissions in recent years suggests that further increase in the use of natural gas may be of limited benefit in decreasing emissions. This is because barring technology-specific policies (for example, Renewable Portfolio Standards); recent studies have shown that gas does not substitute for coal only…

….. Growth of emission-free technologies such as solar, wind and nuclear energy is also limited while gas is cheap…. In these studies, future increases in natural gas use act to both reduce domestic coal use and slow the growth of renewable energy, resulting in little net change to cumulative CO₂ emissions.

…..a growing number of studies also show that increased leakage of methane from new natural gas infrastructure can offset CO₂ reductions relative to coal…

…..Decreases in residential gas prices may lead to rebound effects if people spend some of the money they saved heating their home on carbon- and energy-intensive goods….

…..And finally, decreased domestic demand for coal has enabled an increase in US coal exports to eager and growing overseas markets.”

 The new EPA Clean Power Plan is largely built on fuel switching and renewables deployment.

The article may be found here:

http://www.nature.com/ncomms/2015/150721/ncomms8714/full/ncomms8714.html