April 29, 2011

Shale Gas: A Climate Friendly Fossil Fuel?

A few weeks back, in our article Biggest Drop in U.S. Greenhouse Gas Emissions, we promised to take a look at the implications of a new study that calculated the impact on the earth’s greenhouse effect from the extraction and use of natural gas produced from deep underground shale beds (through a process known as hydraulic fracturing, or “fracking”). The study was conducted by a research team from Cornell University led by Dr. Robert Howarth, and its conclusions were quite surprising:

“Compared to coal, the [greenhouse gas] footprint of shale gas is at least 20% greater and perhaps more than twice as great on the 20-year horizon and is comparable when compared over 100 years.”

The reason that this is surprising (and has a lot of people talking) is that natural gas has long been considered the most “climate friendly” of all the fossil fuels and a potential “bridge” to a low carbon future. The Howarth et al. study now threatens natural gas’s most favored status (at least among climate change-fearing types).

Over at the free market energy blog Master Resource, WCR’s Chip Knappenberger takes a look at the Howarth et al. study, as well as its many criticisms.

As Knappenberger explains, Howarth et al. focus on “fugitive” methane emissions that accidentally escape directly into the atmosphere during the initial stages of the establishing the shale gas wells. As methane is a very powerful greenhouse gas (having some 20 to 100 times the impact of an equal amount of carbon dioxide depending on the period time being assessed), fugitive methane emissions will act to offset the carbon dioxide savings attained when burning the well’s natural gas to produce energy rather than using coal (Figure 1).


Figure 1. Comparison of greenhouse gas emissions from shale gas with low and high estimates of fugitive methane emissions, conventional natural gas with low and high estimates of fugitive methane emissions, surface-mined coal, deep-mined coal, and diesel oil. Top panel (a) is for a 20-year time horizon, and bottom panel (b) is for a 100-year time horizon. Estimates include direct emissions of CO2 during combustion (blue bars), indirect emissions of CO2 necessary to develop and use the energy source (red bars), and fugitive emissions of methane, converted to equivalent value of CO2 (pink bars). Emissions are normalized to the quantity of energy released at the time of combustion. (Source: Howarth et al., 2011).

But, Howarth et al.’s results are derived from few (somewhat shaky) actual observations and sweeping extrapolations there from. And it critics are many.

In his Master Resource posting, Knappenberger summarizes the criticisms this way:

Complaints have surfaced, among others, as to the true global warming potential of methane (Howarth et al. use values that are somewhat larger than reported by the IPCC), the reliability of the little actual data from fracking operations on which the conclusions were based, and whether the “fugitive” methane from the drilling operations actually escapes directly to the atmosphere or whether it is flared at the site (this turns out to make a big difference because if the methane is flared (i.e. burned), CO2 is released to the atmosphere rather than methane).

And, on top of this, since fugitive methane is lost profit, there should be financial incentives to keep it to a minimum (and improvements are anticipated as the fracking methodology matures). And if the market is deemed unsuccessful at reducing the direct methane loss, then in theory regulations could be applied.

The bottom line, according to Knappenberger?

At the very least, the Howarth et al. study has started the natural gas climate bridge swaying a la Gallopin’ Gertie. Whether or not it suffers the same fate as Gertie and crumbles into the abyss only to be rebuilt with a different foundation and design, or whether it manages to stabilize itself and serve as a major pathway to a low(er) carbon future remains to be seen.

In any case, the Howarth et al. study should act to slow early rumblings of a civil war within the fossil fuel family while a more thorough examination of the potential climate impact of the full life-cycle of fossil fuels and their production methods are undertaken.

Be sure the check out the full post Natural Gas: A Better “Climate” Fossil Fuel? for more background and further details including the pros and cons of fracking and how the various fossil fuels stack up in terms of carbon dioxide emitted per BTU of energy produced.

Reference:

Howarth, R. W., R. Santoro, and A. Ingraffea, 2011. Methane and greenhouse-gas footprint of natural gas from shale formations. Climatic Change, DOI 10.1007/s10584-011-0061-5, http://www.springerlink.com/content/e384226wr4160653/




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