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The Damage Done, Part 4 -- Natural Gas, Green or Dirty?

December 27, 2011

Every year, the world produces and consumes about 115 trillion cubit feet of natural gas, generating about 117 quintillion Btus (British thermal units) of energy, this according to the U.S. Energy Information Administration (EIA).

Pie chart US generation by sourceThe EIA say in its 2011 Annual Energy Outlook that natural gas generated about 23 percent of electricity in the U.S. in 2009 and that this is expected to grow to 25 percent in 2035; generation from gas is second only to coal, which provides 45 percent of U.S. power, expected to fall to 43 percent by 2035. The country uses about 26 trillion cubit feet per year. Although natural gas gets used to supply base power demand, one of its more important uses is for peak electricity demand. Gas turbines can be brought online quickly to meet peak demand.

What are the environmental effects of electrical generation from natural gas? While a fossil fuel itself, is gas a cleaner source than coal? Is it dirtier or cleaner than supposedly "green" energy sources like solar and wind? And how do we know for sure? How do we measure the "greenness" of any power source?

That's what I plan to consider in this week's installment of "The Damage Done," a series of articles we are producing here at ThomasNet Green & Clean. In this series, we are attempting to develop an apples-to-apples comparison of the environmental impacts of various sources of electrical power generation, both conventional and renewable.

In our first two articles, I laid out some of the overall environmental issues around energy production. You can read those two pieces at:

"The Damage Done, Part 1 -- Is Green Energy Really Better for the Environment?"

and "The Damage Done, Part 2 -- How Do You Measure the Environmental Effects of Energy?"

The next several articles, one per week, will each consider a particular energy source. We started last week with the Papa Bear of power generation:

"The Damage Done, Part 3 -- Is Coal Really So Bad for the Environment?"

So what about natural gas?

According to the Natural Gas Supply Association,

Natural gas is the cleanest of all the fossil fuels ... [Compared with coal and fuel oil,] combustion of natural gas ... releases very small amounts of sulfur dioxide and nitrogen oxides, virtually no ash or particulate matter, and lower levels of carbon dioxide, carbon monoxide, and other reactive hydrocarbons.

US natural gas production chartHowever, not everyone is so sanguine about the use of natural gas for power generation. As you can see from the EIA chart show here, the growth of gas supply in the U.S. is depending heavily on shale gas. This gas is being extracted largely using the controversial practice known as "fracking," or hydraulic fracturing. In June 2011, ThomasNet's Tracey Schelmetic (see "What's The Big Fracking Deal?" outlined some of the environmental concerns around fracking:

Fracking fluid can be made up of any combination of substances in liquid, gel, or foam form, with any number of chemical ingredients. Among the chemicals used in fracturing fluid is a cocktail of nasty substances that include known carcinogens, skin irritants, and endocrine disruptors - chemicals that affect the healthy function of human adrenal glands that govern development, growth, reproduction, and behavior in people and animals...

Poisoning aside, fracking has also been implicated as the reason behind the "flammable water" phenomenon sometimes encountered in mining country in the U.S.: Tap water from the ground that is so contaminated with chemicals that it can literally catch on fire.

The environmental impact of fracking is under study right now, so it might be a little early to try to quantify its effects. The U.S. Environmental Protection Agency (EPA) released a draft report in December 2011 after studying the effects of fracking on drinking water in a community in Wyoming. EPA's announcement about the report says,

EPA's analysis of samples taken from the Agency's deep monitoring wells in the aquifer indicates detection of synthetic chemicals, like glycols and alcohols consistent with gas production and hydraulic fracturing fluids, benzene concentrations well above Safe Drinking Water Act standards and high methane levels. Given the area's complex geology and the proximity of drinking water wells to ground water contamination, EPA is concerned about the movement of contaminants within the aquifer and the safety of drinking water wells over time.

Natural Gas and Human Health

As I discussed in last week's article on coal, researchers have measured the health effects of energy sources by using a metric called the value of a statistical life (VSL), representing an attempt to assign a dollar value to a human life. If this very idea sends you in a rage, that's what the comment space below this article is for. Before you post your tirade, though, please keep your lid on and first read the explanation of VSL in last week's article. While VSL measures vary considerably, EPA uses a figure of $9.1 million for its studies.

The National Academy of Sciences (NAS) uses a VSL of $6 million in its report, "Hidden Costs of Energy: Unpriced Consequences of Energy Production and Use." The NAS report is useful for our purposes, as it undertakes a survey of the environmental effects of all of the main energy sources. (Photo: Gas power plant, New Hampshire, U.S. Credit: Jim Richmond, CC BY-SA 2.0.)

Gas power plant in New Hampshire, US

Air Pollution From Gas-Fired Power Plants

NAS studied emissions-related damages of key pollutants for 498 power plants in 2005; the pollutants the researchers considered were sulfur dioxide (SO2), nitrogen oxides (NOx), fine particulates (PM2.5), and coarse particulates (PM10). These 498 were plants that generated at least 80 percent of their electricity from gas. They accounted for 71 percent of gas-generated electricity in the U.S. in 2005.

The study calculated average annual damages of $1.49 million per plant. Damages at gas-fired plants were much lower than those at coal-fired plants. One reason is that gas plants tend to be much smaller than coal plants. However, they also do less damage per kilowatt-hour (kWh). On average, damages at gas plants are .16 cents ($.0016) per kWh, as opposed to 3.2 cents ($.032) for coal plants. However, the study notes that damages per kWh vary widely among plants. The 10 percent of plants with the highest damages account for 65 percent of damages from all 498 plants.

The following chart outlines key figures about damage done by the four chief pollutants. This chart is similar to the one I showed in last week's article about coal:

Pollutant Mean Damages per Ton of Emissions (2007 $US) Mean Damages per Kilowatt Hour (2007 $US)


$.00018 (0.018 cents)



$.00230 (0.230 cents)



$.00170 (0.170 cents)



$.00009 (0.009 cents)

The figures for mean damages per ton of emissions are higher for natural gas plants than for coal plants because of the locations of the plants. If you think about it, a power plant located near an urban area will do more human damage than one located in the country, all other things being equal.

Chart showing electrical generation by source 2008-2035EIA data say that worldwide generation from natural gas was 4.2 trillion kWh per year in 2008, expected to rise to 4.9 trillion kWh in 2015. Let's extrapolate and estimate the figure as 4.6 trillion kWh per year as of the beginning of 2012.

Taking that figure of 4.6 trillion kWh of power generation from natural gas and multiplying it by NAS's mean cost in damages of ($.0016) per kWh, I estimate that the annual damages from worldwide natural gas power generation come to $7.36 billion.

Let's run the comparable calculation for coal. The same EIA data would yield a total yearly generation from coal plants as of the beginning of 2012 of 8.2 trillion kWh per year. NAS estimates mean damages for coal as $.032 per kWh. This would yield an estimate of annual damages from worldwide coal power generation of $262.4 billion per year. This is comparable to the figure I stated in last week's article about coal generation, although that estimate was based on 2005 generation figures.

Natural Gas and Climate Change

Greenhouse gas (GHG) emissions offer another means to compare the environmental effects of power generation. Carbon dioxide (CO2) is the GHG most often mentioned in discussions about human-caused global warming, but water vapor, methane, nitrous oxide, and ozone are also considered GHGs. For simplicity's sake, GHG emissions for electricity generation are usually wrapped all together in a single "carbon footprint" measure, expressed in "carbon equivalents" using the metric "gCO2eq/kWh." This stands for "grams of CO2-equivalent per kWh." (For more explanation of this metric, see the U.K. Parliamentary Office of Science and Technology's report, "Carbon Footprint of Electricity Generation.")

A study by Benjamin K. Sovacool of the Vermont Law School is useful for comparing the carbon footprint of various power sources. (See "Valuing the greenhouse gas emissions from nuclear power: A critical survey," Energy Policy, 2008.)

Sovacool estimates the lifecycle carbon footprint for natural gas power generation at 443 carbon equivalents. While high compared to nuclear, solar, and wind, that figure is less than half of the carbon footprint of coal. The following table shows how the various sources compare, according to Sovacool's research:

Source/Technology Lifecycle CO2 Equivalents (gCO2eq/kWh)
Coal 960-1050
Natural gas 443
Nuclear 66
Solar Photovoltaic (PV) 32
Wind 9

Given the growth of natural gas power generation, we can expect the CO2 impact to grow as well, as indicated in this EIA chart:

Chart showing world CO2 emissions by source

Overall, then, we could say that by measures that are available, natural gas does a fair amount of environmental damage, but less than coal. That's why some observers have advocated using gas as an alternative to decrease reliance on coal, while power generation transitions to renewables over the coming decades.

But do other power sources offer a less-damaging way to produce electric power? In coming weeks, we will go on to consider the environmental impacts of nuclear power, hydro, solar, and wind, asking our core question, How do we know what kind of energy is truly "green"?


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