I am often disappointed with the quality of reporting on energy issues in the national media.   The recent slate of reports on reductions in U.S. carbon dioxide emissions, stemming from many U.S. power plants converting from coal to natural gas are no exception.   Although many of these reports are interesting and well written, for the most part, they leave the reader with an incorrect understanding of the true environmental impact of this transition.  As an example, here is a report from the Newark Star Ledger from August 16 entitled “Natural Gas Prices Drive CO2 Emissions to 20-Year Low.”  I’ll conclude with my critique of this article, but first the science.
As I covered previously in “Electricity Production 101,” traditional power plants burn fossil fuels to generate electricity.  Historically coal has been cheaper, on a dollar per unit of heating energy basis, than petroleum oil or natural gas.  Therefore, over the last century, the vast majority of electric power plants have used coal.
The introduction of hydraulic fracturing (“fracking”) to access previously unrecoverable deposits in underground shale formations, has dramatically increased the supply of natural gas (methane) in the U.S. over the last 5-10 years. (For the details on fracking see my previous column “To Frack or Not to Frack.”)  The increase in supply has resulted in a dramatic reduction in the price of natural gas, influencing many electric power plants to convert from coal to natural gas.  At first glance this appears to be a very positive environmental trend, but further review provides a more complex and less rosy picture.
The environmental appeal of natural gas stems from the fact that less carbon dioxide is emitted per unit of electricity produced.  Consequently, the headline from the Star Ledger article linked above, and hundreds of others just like it, are, in a limited sense, accurate.  They are just not useful. They give the impression that the “natural gas boom” in the U.S. is resulting in a net positive impact on global emissions of green house gases.  This is simply not true.
All of the articles I have read on this topic omit any discussion of the environmental impacts of the fracking process.  In order to fracture the shale formations, millions of gallons of water are pumped, at very high pressure, into the ground.  The solubility of a gas, like methane, in water is proportional to pressure.  Therefore, in the high pressure environment of the underground shale formation, a significant amount of methane is dissolved in the water.  After the shale formation is fractured, the water is pumped back out of the well.  Once the water returns to the surface, where the pressure is now lower, much of the dissolved methane is emitted in to the air.  Methane is approximately 20 times more effective in trapping heat in the atmosphere than carbon dioxide.  Once you include the methane emissions, natural gas from fracking operations loses its advantage over coal from a greenhouse gas perspective.
The second, and more important, gap in these articles is that reductions in U.S. carbon dioxide emission rates, though interesting, are not the appropriate proper parameter to examine if one is concerned about global warming.  Since gases in our atmosphere are well mixed, all that matters is the total amount of carbon dioxide emissions, not the locations where the emissions occur.  Therefore, converting power plants in the U.S. from being coal-fired to natural gas-fired can only reduce global carbon dioxide emissions if it results in a global reduction in coal use.  But that is not happening.
Since coal companies are losing market share in the U.S., they are increasing exports to places like China and India.  In fact, U.S. coal exports doubled from 2009 to 2011 and are increasing again this year.  In the end, the same amount of coal from U.S. mines is being burned as before the natural gas boom, some in the U.S. and the rest around the globe.  On top of this, the amount of natural gas being burned is now much higher.  So the real news story here is that the increased supplies of cheap natural gas in the U.S., unlike the impression you get form the Star Ledger article and others like it, are dramatically increasing global carbon dioxide and methane emissions.
So how should we consider and evaluate environmental issues related to fossil fuel-based energy production?  The key is to focus on the rate of extraction of fossil fuels from the ground.  Because if we’ve mined it or drilled it, you can be certain that we are going to burn it.  You will know we’ve really started to make progress when you see a news article with a title that says “Expansion of Solar Power Generation in China and India Reducing Demand for Coal”.  Then you’ll know we’ve turned the corner.
Have a comment or question?  Use the comment interface below or send me an email at commonscience@chapelboro.com.