There are two other easy-to-see effects. The fracking for oil that has opened vast new supplies of gas is producing much of it in places where there is no pipeline. In those cases, the natural gas is burned off, or flared, because there is no way to ship it economically.
According to the Energy Information Administration, last year the producers flared enough gas to have produced 27 million megawatt-hours. That pushed emissions up by 16.5 million tons, about 15 percent as much as the reduction in coal burning saved.
And some of the natural gas escapes unburned. Its main component, methane, is a global warming gas and is far more powerful than carbon dioxide, although it does not persist quite as long in the atmosphere. Even before fracking became widespread, when natural gas was expensive to extract, there were emissions of methane. But from 2007 to 2013, the increase in gas consumption added methane with a carbon dioxide equivalent of about 19 million tons. That would wipe out another 17 percent of the savings from displacing coal. The number could be higher; some experts use a different formula to translate methane into a carbon dioxide equivalent.
This is a very strong, thorough article about the reality of the natural gas boom. The concept of “bridge fuels” is a false concept. They only serve as a way to prevent the transition to renewable energy.