At present coal-fired power plants produce 40 percent of the world's electricity; natural gas-fired power plants produce 21 percent of the world's electricity.
Per thermal unit produced, combustion of natural gas produces half as much carbon dioxide, less than one-third of the nitrogen oxides, one percent of the sulfur dioxides, and less mercury than does the combustion of coal.
One-half of the mercury released into the environment in the US comes from the combustion of coal in coal-fired power plants.
So why oppose the replacement of coal-fired power plants with natural-gas fired power plants, domestically and overseas?
First: Switching from one fossil fuel to another maintains dependence on fuels that have finite supplies and that accelerate climate change.
Second: A lifecycle assessment of any substance includes all emissions and effects from source to consumption, and its persistent effects in the environment and the atmosphere. When the lifecycle assessments of natural gas and coal are compared, natural gas loses. As the table below indicates, over a 20-year timeframe, the greenhouse gas emissions from shale gas (fracked gas) are 43 percent greater than those of coal. Methane is the principal contributor to this reality. When the table was created, methane was thought to be 25 times more potent than carbon dioxide as a greenhouse gas. Now, methane is thought to be 34 times more potent.
Over a 100-year timeframe, there is little difference in the lifecycle assessment between between coal and natural gas. By the time that century has passed, both sources of fuel will likely have been long depleted.
There is a profound environmental paradox inherent in switching from coal to natural gas to generate electricity. Emissions from the combustion of coal contain far more particulates than do the emissions of natural gas. Coal emissions, while poisoning the air, help to cool the planet - relatively speaking - by blocking sunshine and decreasing the greenhouse effect, a process known as global dimming. So a wholesale switch from coal to natural gas could be a trigger for short-term accelerated climate change even if natural gas had fewer emissions in its lifecycle.