Could natural gas emissions exceed coal? The case for gas with CCS | Global CCS Institute

Though natural gas extracted from shale is the fastest growing energy source for power plants in the U.S., shale gas is now facing fresh challenges, with the release of a new study suggesting the fuel’s carbon intensity is as high as or higher than coal’s.

Given the rapid growth of natural gas, the findings could upend a consensus view that it’s a greener alternative to coal. The natural gas industry maintains that the fuel emits only about half the CO2 of coal, and therefore has promise as a “bridge” from today’s carbon-intensive fuel mix to future low-carbon options. The new findings suggest that, if natural gas emissions are undercounted, there’s greater urgency to develop CCS for natural gas plants, alongside coal.

Already, the low cost of natural gas—along with its low emissions of conventional air pollutants—has led many utilities to shutter older, dirtier coal plants and replace them with gas turbines.  Earlier this week, for instance, the Tennessee Valley Authority (TVA) agreed to a landmark deal with the US Environmental Protection Agency (EPA) to shutter 11 of its most polluting coal plants, replacing some with natural gas.

Yet if shale gas is as carbon intensive as coal, the results of swapouts like these could cause greenhouse gas emissions to actually rise.

“Compared to coal, the footprint of shale gas is at least 20 percent greater and perhaps more than twice as great on the 20-year horizon and is comparable when compared over 100 years,” Robert Howarth, a Cornell ecologist writes in a pre-publication version of the paper, originally obtained by The Hill newspaper, and which can be viewed here.

The gist of Howarth’s findings has been made public in the past and are already being fiercely debated. The issue has been re-energized since the study is being published in a peer reviewed scientific journal, Climate Science, boosting their credibility.

It’s important to emphasize Howarth’s findings are based on natural gas extracted from shale reserves, rather than natural gas from conventional reserves.

That said, prior analysis, including one by the EPA, have put to the test claims that natural gas emits 50% less green house gases than coal, as is often claimed. Earlier this year, as detailed by ProPublica, the EPA issued analysis (see the report here) that methane leakage during transmission and processing may cut in half the advantage that is frequently attributed to natural gas.

Howarth and his colleagues—Anthony Ingraffea and Renee Santoro, also at Cornell—contend the process of hydraulic fracturing releases far more methane than conventional drilling.  When fluids, which are pumped into the well to crack open shale and release the gas, resurface to be reused, they release large volumes of methane, according to the study. Howarth is quoted by the New York Times, saying:

“…we came up with two things that surprised me. First, I expected the indirect CO2 emissions from trucks moving frac water, the compressors, the drills, etc., to be greater than we found. They are actually pretty small, when you add up all the numbers. And second, the influence of methane is greater than I expected…”

Howarth’s finding could fuel critics of shale gas, especially in Northeast US states, where public anxiety is rising that fracking threatens underground sources of fresh water.