The annual EPA report on greenhouse gases – Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2011 – published this past month, is striking for its findings on both carbon and methane and the impact of natural gas on the environment. Its findings include evidence that is favorable to natural gas relative to two very important greenhouse gases: carbon and methane. The findings associated with methane are especially important because they will be surprising in light of recent media reports. The EPA report shows a decline in methane, raising serious questions about the methodology and findings of recent studies of ambient methane release associated with natural gas extraction.
Natural gas is increasingly becoming the fuel of choice for electric power generation. There are many reasons for this, but an important one has been the relatively lower production of atmospheric carbon from natural gas. However, the rationale for the transition to natural gas in the power industry goes well beyond its comparative advantage in friendliness to the environment from lower release of carbon. Since 2009, the price of natural gas has declined while that of coal has risen. Contributing substantially to the increase in supply of natural gas and its lower price has been the extraction method known as fracking. Hydraulic fracturing of shale – or fracking – involves fracturing layers of underground shale using high-pressure injection of liquids. The newness of the process has raised a variety of environmental questions.
When examining the impact of natural gas on the environment, it is important to understand why it is considered a cleaner fuel source. Natural gas is a lower carbon intense fuel. It produces the same unit of heat or electricity with a 55% lower carbon content than some other fuels such as coal. US greenhouse gas emissions declined from 2007 to 2011 as a result of “a decrease in coal consumption, with increased natural gas consumption and a significant increase in hydropower used.”
Nevertheless, the increasing use of the fracking process for extraction of natural gas from shale has been questioned for its environmental friendliness, particularly from the potential for increased methane production. Among the questions has been a set dealing with the potential that the process has for producing unintended emissions of greenhouse gases that offset the advantage of the lower carbon intensity of natural gas. Of particular attention has been the production of methane in what has been referred to as fugitive methane emissions. Methane has more than 20 times the capacity of carbon for trapping heat in the atmosphere. The Intergovernmental Panel on Climate Change reported that atmospheric methane has increased by 158% over the last 250 years.
The annual EPA report adds very important information about natural gas and fugitive methane emissions. While natural gas remains a large potential source of methane, emissions of methane have decreased since 1990. This decrease occurred at the same time that the supply of natural gas has increased substantially, at the same time that the fracking process was introduced for extraction of natural gas, and, most importantly, at the same time use of natural gas has increased. In examining specifically the issue of methane production from fracking, the EPA report compared current findings of its Inventory with its Greenhouse Gas Reporting Program (GHGRP). There are unreconciled differences between these two reports. Moreover, the GHRP data “show lower overall methane emissions from well completions with hydraulic fracturing and workovers with hydraulic fracturing (refracturing) than calculated in this inventory.”
Clearly more studies will examine the issues of methane production from the fracking process. The EPA will also work to reconcile data from different methodologies for measuring greenhouse gases. But overall data from this Inventory are simply inconsistent with what has been reported from some studies about the impact of fracking on methane production.