Within the next 4 years, total carbon emissions from natural gas probably will exceed emissions from coal, but America's total carbon emissions will likely fall further as a consequence. Here is why.
As gas displaces coal in power generation, the shale gas revolution drives down carbon emissions from coal, increases emissions from natural gas, and cuts total US carbon emissions, because the decrease in emissions from coal are much greater than the increase from gas production.
At the start of EIA records in 1973, US carbon emissions from coal and natural gas were almost the same, with coal emitting just 29 million tons than gas. As the nation turned to coal to make electricity, carbon emissions from coal nearly doubled and were 1 billion tons more than natural gas by 2005.
Just as US carbon emissions from coal peaked in 2005, shale gas production began to zoom upward. One result of cheap gas was that coal's carbon emissions dropped 73 million tons per year since 2007, as gas took generation market share from coal.
Another result of cheap gas and more gas usage is rising carbon emissions from natural gas, as the economy shifts from both coal and oil to natural gas. Carbon emissions from natural gas rose a total of 121 million tons since 2007 or 24 million tons per year over the five year period.
By 2012, the spread in carbon emissions between coal and natural gas that had been 1 billion tons in 2005 was down to 300 million tons. If one assumes both that emissions from coal will decline on average 73 million tons per year and that carbon emissions from natural gas increase by 24 million tons per year, natural gas will emit more carbon than coal by 2016.
The more than 100% increase in natural gas prices since April 2012 and the return to $4 per thousand cubic feet gas does call into question the current trend of decreasing carbon emissions from coal and increasing carbon emissions from gas will continue. Market forces in early 2013 have reversed and are moving toward coal and away from gas for generation.
EPA's Air Toxic rule, however, takes effect in 2015 and natural gas plants meet that requirement, while old-coal fired power plants without pollution controls do not. A mid-range estimate of coal plants that will retire, as a result of the EPA rule, is about 50,000 megawatts.
By 2015 and 2016 another big drop in carbon emissions from coal plants will occur as a result of the EPA Air Toxic rule. As those coal plants retire, natural gas generation will substantially take their place, and that combination could well mean that carbon emissions from natural gas will exceed those of coal by 2016.