Natural gas is hailed as a "clean" burning fuel. In other words, greenhouse gas emissions are lower than coal's emissions.
In November of 2010, Cornell University stated that, although it is true that natural gas releases less carbon dioxide than coal per unit of energy when lit, this is only part of the picture. They claim that this analogy is misleading.
They looked at natural gas and coal production over a 20 year estimate. They compared three aspects of natural gas and coal production: direct, indirect and methane emissions.
Direct emissions are calculated when the gas is, literally, on fire, such as when you're cooking on a gas stove or warming your home with gas logs. The direct emission analogy is what "clean" burning fuel is based on.
Indirect emissions consider the CO2 emissions released regarding actual production. In other words, they probably evaluated fracking sites from the initial site assessment to the clear cutting of trees to laying down the pipes. Big tankers continually travel to each well pad during the pad's lifecycle. Just ONE on the interstate makes me hold my breath.
Methane is emitted from natural gas and coal production. Have you ever been on or near a site and noticed a lit flame? That's methane. The study converted the methane emissions to the equivalent value of CO2.
The study added the direct, indirect and methane emissions and concluded that "natural gas is no better than coal and may in fact be worse than coal in terms of its greenhouse gas footprint when evaluated over the time course of the next several decades."
Although the article has not been peer reviewed yet, Cornell felt that that findings were very important and released the summary graph anyway.
Reference
http://www.eeb.cornell.edu/howarth/GHG%20emissions%20from%20Marcellus%20--%20November%202010.pdf
