Some years stand out and 1973 is just one such year. It was the year of the first oil price shock, triggered by an embargo of oil to the USA, and 1973 is the start of the EIA data on carbon emissions from coal.
Now 40 years ago, carbon emissions from coal were 1.2 billion tons and they had nearly doubled to 2.182 billion tons in 2005, when they peaked. In the last 7 years, coal's emissions have rolled back 26 years.
By last year, coal's emissions were back to 1986 levels at 1.66 billion tons, after an enormous plunge during 2012, when gas displaced huge amounts of coal-fired generation. Just in 2012, emissions from coal dropped an astonishing 222 million tons, or close to 12% of the 2011 total. Wow! Wow!
Coal's emissions fell so much during 2012 that carbon emissions from natural gas exceeded those from coal during January and February of 2012. Not since probably 1980 or earlier had gas emitted more carbon than coal for a full month.
Since the peak of coal's emissions in 2005, coal's carbon emissions dropped 516 million tons in 7 years or an average of 73 million tons per year. At that rate of decrease, coal's carbon emissions will be back to 1973 levels by 2020.
Coal's carbon emissions may not reach the level of the historic 1973 by 2020, but they will sooner or later. It's not a question anymore of if but when.