The Shale Quandary

Does the good outweigh the bad?

The U.S. Energy Information Administration’s report on “Emissions of Greenhouse Gases in the United States 2009” was officially released on March 31st. Two of its key conclusions:

  • Total U.S. emissions of carbon dioxide (CO2) and other greenhouse gases were down by about 5.8 percent relative to 2008 — a large drop to be sure; but
  • CO2 emissions related to energy generation were down by a whopping 7 percent related to 2008.

Given that the country was mired in its most severe recession in three quarters of a century, it’s not all that surprising that emissions were down — after all, emissions are related to economic activity, so when economic activity tanks so should emissions. Kinda like the saying that there’s a silver lining in every cloud.

But upon further inspection, I was surprised by the EIA’s data on the causes of the drop in emissions — the recession does not tell the whole story.

The decline in U.S. gross domestic product was 2.6 percent in 2009. That alone cannot explain a decrease of 5.8 percent in total emissions and 7 percent in energy-related emissions. What caused the remainder? The EIA’s analysis identified two other factors:

  1. A 2.2 percent decrease in energy intensity (the amount of energy produced per unit of GDP). The decrease reflects both the economic hit that energy-intensive industries took and an ongoing, long-term national trend that’s typical of most economically advanced countries, in large part due to the shift from an industrial to a service-oriented economy.

    And, and perhaps most interesting:

  2. A 2.4 percent decrease in the so-called carbon intensity of our energy generation, defined as the CO2 emissions per unit of energy generated. That reflects the largest annual decrease in carbon intensity since the 1990s [pdf].

In other words, the decrease in carbon intensity was almost as important as the economic downturn in driving down our greenhouse gas emissions in 2009!

So, the question naturally arises…

What Caused the Decrease in Our Energy Supply’s Carbon Intensity?

Well, a very small part of it came from the growth of renewable energy whose consumption increased by 5.4 percent from 2008 to 2009.

But the lion’s share of the decreased carbon intensity came from fossil fuel substitution. The simultaneous increase in coal prices along with the precipitous drop in natural gas prices encouraged those power companies able to tap natural gas to use it over coal. (See Figure) And what has caused the drop in natural gas prices? Hydraulic fracturing, a k a hydrofracking — the technology that’s allowed natural gas extraction from shale and that’s single-handedly increased the country’s potentially recoverable resource of natural gas by leaps and bounds. Proved reserves of shale gas grew by 76 percent between 2008 and 2009.

% of total energy derived from coal and natural gas
The nation has seen a trend toward switching from coal to natural gas. But is the green color given to natural gas in the figure appropriate? (Data obtained from the Department of Energy, Table A2.)

Cool, right? Maybe not. This is kinda like the cloudy dark shadow sliding on over the apparent natural-gas silver lining.

Are Greenhouse Gases from Natural Gas All That Low?

When you burn natural gas, the amount of CO2 emitted is a whole lot less than what you get when you burn coal — about half as much. So far so good. But there’s another way for natural gas to affect the climate. It comes from fugitive emissions — inadvertent releases of methane during extraction and transport.

Because methane, the major component in natural gas, is many times more effective as a greenhouse gas warmer than CO2, any escape of methane into the atmosphere can exact a relatively large global warming price.

Unlike coal, a large chunk of natural gas emissions are released during production and distribution, but given that it burns so much cleaner than coal it only emits about half of the overall emissions of coal when you consider all emissions from extraction through combustion. But a new paper on this subject by Robert Howarth from Cornell University and colleagues, to be published in the journal Climate Change Letters, disputes this conclusion. The paper has already received a good deal of media attention (see here, here and here) — even though it has not yet been actually published.

Howarth et al argue that the fugitive emissions from mining shale gas are so large that they make natural gas worse than coal from a climate perspective. These results have, not surprisingly, been disputed by the natural gas industry. I suspect that the Howarth et al results will prove to be overstated, but that is a subject for another day.

Don’t Forget the Environmental Toll

Extracting natural gas from shale has an environmental cost — some might say an unacceptable cost. A lot of that cost may be paid in water — or more specifically, potential water contamination of wells and aquifers (see here, here and here) as well as surface water contamination from spills. It also can include the disruption of communities from the constant roll of trucks bringing water to and hauling contaminated water away from drill sites. 

And there is the environmental quandary. Are the environmental costs of shale gas worth the putative climate benefits?