In its July-August 2012 issue of SIERRA magazine, the organization explains in detail the reasons for its hardening stand. At first the Sierra Club took a fairly hopeful wait-and-see attitude, based on the fact that shale gas burns much cleaner than other fossil fuels.
But then the evidence started piling up that the damage done before the fuel is burned more than offsets its clean burning. In fact, fracked shale gas is starting to look like the dirtiest fossil fuel, particularly in terms of climate change.
Perhaps most damning, recent in-depth studies of fracked wells by scientists at Cornell University, the University of Colorado and the National Oceanic and Atmospheric Administration all show that large amounts of raw methane leak into the atmosphere during drilling. One study asserts that nearly 8 percent of fracked methane can leak into the atmosphere.
Methane is some 30 times more potent as a greenhouse gas.