There is no disputing that US carbon emissions are plummeting. First, carbon dropped 9% or 549 million tons from 2007 to 2011. www.eia.gov/totalenergy/data/monthly/index.cfm. Then, from January to May 2012, emissions declined another 6% or 144 million, when compared to the same period in 2011.
While no dispute exists that US energy related carbon emissions are way down, controversy has erupted in some quarters over the role of gas in producing the sharply lower carbon emissions. It's become an energy "who done it?"
For the period from 2007 to 2011, more gas, more renewable energy, and more efficiency cumulatively caused respectively carbon emissions to drop from burning coal and oil by 305 and 304 million tons. My estimate is that gas displacing coal and oil accounted for about half of the decline between 2007 and 2011.
Yet, while gas played a big role prior to this year in reducing carbon emissions, gas's role in cutting the 2012 emissions to date is even bigger. In fact, gas is likely responsible for about 80% of the 2012 emission decline to date. Consider the following data.
The entire carbon emission decline in 2012 comes from falling carbon emissions from coal and oil and disproportionately from coal. From January to May 2012, coal emissions fell 132 million tons or from 756 million tons in the same 2011 period to 624 million tons. That is an 18% decline and almost entirely as a result of more gas displacing coal generation this year. Indeed, coal's electricity generation market share fell from 42% for all of 2011 to 32% in April and 34% in May.
By comparison to coal, oil carbon emissions dropped a modest 18 million tons or 2% in the first five months of 2012, compared to the same period in 2011. Total oil emissions were 937 million tons so far this year, down from 955 million tons in 2011.
As a result, about 85% (132 of 144 million tons) of the 2012 US Carbon emission decline is a product of falling emissions from coal. So one answer to the question, "what done it?" is that emissions from burning coal are way down.
But what caused coal emissions to decline in 2012? Is consumption of electricity way down? Did the economy shrink in 2012? Are renewable energy or nuclear power shoving coal off the grid this year? Or could it be that natural gas is displacing coal to generate electricity? What done it?
It's not a shrinking economy. The nation's GDP has increased every quarter since July 1, 2009. And our GDP is bigger than in 2007, when carbon emissions peaked, and prior to the economic meltdown from November 2007 to June 2009.
It's not renewable energy or nuclear. Nuclear power production is about flat between 2011 and 2012.
As a result of a big drop in hydro, total renewable production is down in 2012 compared to 2011 so renewable energy this year is not displacing more fossil fuels in 2012 than in 2011. It will actually displace marginally less this year than it did in 2011.
Electricity demand is down 2% in the first 5 months of 2012 compared to 2011 so that is a small reason for declining emissions and probably explains about 10% of the 132 million ton decline of coal emissions.
Even if one incorrectly assumes that gas had nothing to do with the 2% (18 million tons) decline in oil emissions, and if one attributes 11% or 15 million tons of the coal emission decline to reduced electricity demand in 2012, natural gas displacing coal is conservatively still responsible for about 110 million tons of the 144 million ton decrease in 2012 carbon emissions during January to May 2012. That is about 77% of the total decline this year to date.
Since gas is displacing more coal and oil than anything else, natural gas is cutting carbon emissions in the US more than anything else. That is a fact!