Wednesday, May 22, 2013

Recent Trends in U.S. GHGs

The latest EPA report relating to U.S. GHGs is in for 2013, so this seems like a good time to review that data and see what else we can say.  EPA’s 2013 report compiles data through 2011, but there is other information that can help us see what probably occurred in 2012. 

The 2013 EPA report indicates that total U.S. GHGs in 2011 fell by 1.6 percent relative to 2010.  These emissions were 6.9 percent lower than total U.S. emissions in 2005.  An EPA graph showing U.S. emissions since 1990 is reproduced as Figure 1 below.  As can be seen there, the U.S. total has been trending downward since about 2006. 

Figure 1.  Total U.S. GHG Emissions

Why has this been happening?  For one, the U.S. economy was in recession during some of that time, resulting in a contraction of economic activity and thus a reduced demand for energy.  For another, large new supplies of natural gas have been coming onto the market, leading to displacement of coal among power producers.  Gas consumption has approximately half the GHG content of coal on an energy-equivalent basis. 

EPA compiles data for all forms of GHGs, not just those from the burning of fossil fuels.  However, carbon dioxide is by far the largest single contributor to the annual total, making up approximately 85 percent.  Therefore, if we know what happened to GHGs from fossil fuel consumption in 2012, we’ll have a pretty good idea of what happened to the total.

The Energy Information Administration (EIA) compiles data relating to fossil fuel consumption.  Its numbers for 2011 and 2012 are shown in Table 1.  As can be seen there, coal and oil consumption dropped in 2012 while natural gas consumption rose.  These numbers suggest that U.S. CO2 emissions probably dropped in 2012.  This is confirmed by EIA.  According to that source, total U.S. CO2 emissions from fossil fuels fell from 5498 million metric tons (mmt) in 2011 to 5288 mmt in 2012, a decrease of 3.8 percent.  While we do not know the behavior of other U.S. GHGs in 2012, it seems likely that the overall 2012 number, when it is published in 2014, will show another decrease. 

Table 1.  U.S. Fossil Fuel Consumption in 2011 and 2012 (quadrillion BTUs)
Natural Gas

Up to a point, this is good news.  It appears that increased fuel economy in the nation’s vehicle fleet in 2012 probably accounts for much of the decrease in oil-related emissions, and substitution of natural gas and renewables for coal in the power sector likely drove down emissions there.  However, some of the coal not burned in the U.S. was exported elsewhere, where it contributed to other country GHGs.  Whether those GHGs would have been as high without the U.S. coal is a complicated question, too much so to get into here. 

Summarizing, U.S. GHGs have been trending downwards, at least through 2012.  It’s too early to say much about 2013, but the drivers of reduced emissions during the past couple of years remain in place.  Still, more rapid economic growth probably would result in greater use of energy and more GHGs.  Thus, recent annual declines in U.S. GHGs may slow or even reverse.  In other words, if we want to see the recent trend continue, we’ll probably have to take collective action at some point to make it happen. 

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