Ideas

Natural Gas or Coal: It’s All About the Leak Rate

June 24, 2016

Oil and gas field equipment, Industrial waste, scoured land and polluted air now cover much of the sage flats in the area know as the Jonah field. Photo © David Stubbs

When it comes to generating electricity, coal is a dirty fuel. It’s dirty to mine, dirty to burn, and dirty to dispose of the ash. (See my blog). But, until recently coal was the cheapest fuel for electric power, so it has been widely used across the U.S. by the electric utilities. Last year about 32% of our nation’s CO2 emissions came from coal-fired power plants.

Now, two factors are pushing for a switch away from coal — President Obama’s commitment to reduce carbon dioxide emissions to reduce global climate change and the low price of natural gas, which is now competitive with coal in electric power plants. There is widespread interest natural gas across the electric utility industry, because various studies indicate that burning natural gas rather than coal can reduce CO2 emissions by about 40% for the equivalent amount of power generation. Utilities, such as Duke Energy, are proposing new natural gas-powered power plants, with the goal of reducing their CO2 emissions.

Environmental advocates face a dilemma with respect to natural gas — it is cleaner, but about half of our natural gas is now derived from hydraulic fracture (i.e., fracking) methodology, which many environmentalists oppose. And, natural gas is a fossil fuel that releases CO2 to the atmosphere.

From the mine to the power plant, there is little loss of coal to the environment. Unfortunately, that is not the case with natural gas, where there are leaks in the oil field, leaks from the pipeline distribution system, and leaks from storage. At least one study indicates a lower rate of leakage from natural gas fields using fracking, compared to conventional gas fields.

Leakage of natural gas, which is predominately methane, has another drawback. Methane is a powerful greenhouse gas that exerts about 86 times the global warming potential in the atmosphere compared to CO2 during the first 20 years after emission. The concentration of methane in Earth’s atmosphere is increasing every year, although it is not at all certain whether this is due to greater leakage of natural gas or increases from other sources, such as wetlands. Leakage from oil and gas fields makes a significant contribution to the annual emissions of methane to the atmosphere.

Aerial view of a giant mining shovel being used for mountain top removal during open pit coal mining in the Appalachian highlands of West Virginia. Photo © Kent Mason
Aerial view of a giant mining shovel being used for mountain top removal during open pit coal mining in the Appalachian highlands of West Virginia. Photo © Kent Mason

In any case, we need to include the emissions of methane from leaks in the natural gas distribution system in any comparison with coal. Consider the following: In burning coal about 25 grams of carbon are emitted to the atmosphere as carbon dioxide per MJ of energy produced. With natural gas, only about 15 grams of carbon are released. At first glance, gas looks great.

The leak rate of natural gas averages about 1.5% of production. Over a 20-year-period, a leakage rate of 1.5% would give natural gas nearly twice the impact on global climate change versus coal. I pick a 20-year period for the calculation because that is taken by many atmospheric scientists to be the window-of-opportunity we have to prevent harmful levels of climate change. By that account, switching to natural gas is a really bad idea.

Indeed, any leakage rate above about 1% of gross production negates the advantages of natural gas with respect to mitigating climate change. No surprise that the natural gas industry reports that the average leak rate in the U.S. is only about 0.42% of gas production, but individual studies report larger values. The leak rate also varies widely among U.S. cities. Incidentally, the recent leakage from the Porter Ranch natural gas storage facility in California amounted to 0.01% of annual emissions in the U.S.

As the arguments for coal versus natural gas play out in the coming months, the choice will depend upon the leak rate for natural gas. If you want to hedge your bets, encourage your power company to invest in wind, solar, tidal or geothermal power. These are now cost-competitive with coal and offer a no-regrets future.

This post originally appeared on William H. Schlesinger’s blog Citizen Scientist, published by Duke’s Nicholas School of the Environment.

William H. Schlesinger

William H. Schlesinger is one of the nation’s leading ecologists and earth scientists and a passionate advocate for translating science for lay audiences. A member of the National Academy of Sciences, he has served as dean of the Nicholas School of the Environment at Duke and president of the Cary Institute of Ecosystem Studies. More from William H.

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3 comments

  1. No, the alternative energy sources are much more expensive than natural gas. Do not accept this blatant falsity. Also, deny the global warming lies and hysteria.

  2. Dear Sir

    There is a major oversight in this discussion. Mines, specifically in this case coal mines. Studies since the 1970’s have identified methane emissions from coal mines. An active coal mine will emit as much methane to the atmosphere as a good “fracked” natural gas well OPENED to the atmosphere. In the US alone there are 600 active coal mines, there are 500,000 abandoned mines. In addition, there are smouldering coal mine fires, more than 100 in Pennsylvania alone; fires releasing yet to be measured quantities of various gases. Considering the ENTIRE coal energy industry, there are massive methane, mercury, radon, NOX, SO2 emissions, and of course fly ash. The natural gas power generation industry could eliminate most of these emissions in 5 years, saving my trees from an acid rain death. Many solar farms due financial incentives are located on clear cut lots.
    China and India have thousands of methane emitting coal mines. China the producer of our solar panels and some wind turbines have massive pollution from mining and refining the rare earths required to produce both; also consider vast quantities of materials that must be mined, and the MINES themselves as methane emitters. Don’t forget all the diesel that must be used for mining and to power our trucks.
    Natural Gas fired electric generation can be constructed at an astonishing rate, it’s happening now, simply for profit.
    Imagine one clean pristine snowfall at the poles, a very non-linear effect, I imagine, due to elimination of soot from diesel and coal, easily in 5 years. It would seem at this time ice and snow melt is the most immediate problem. Maybe mercury in our food and atmosphere?
    Please do reconsider the “leakage” of methane that could be eliminated in five years. Why are hundreds of thousands of mines ignored? Miners could work for decades plugging these mines.

  3. Dear William. The above insights are vital- for the better understanding- in the Energy sector, and overall- of what direction of change we are to adopt in and over our energy architectures. With the present incumbents pressing for a coal vds. gas replacement, and whereby Gas is largely to be commoditized into global LNG shipping schemes ( with a 2-6 % leakage rate during shipping)- combined with the ever intense fracking of fields- doesnot make good bedtime reading, if we are to assume the present realities as we see being discussed at COP23.

    I will be happy to listen to your education opinion, and work with you- to see our energy industry heal, and become so much better.