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U.S. CO2 Emissions Have Been Falling--Will That Continue?

Dan Lashof

Posted April 9, 2013

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A version of this blog first appeared in Live Science's Expert Voices: Op-Ed & Insights.

The Energy Information Administration (EIA), the official U.S. energy data keeper, recently released full-year 2012 data. They show a 3.7 percent reduction in carbon dioxide emissions from fossil fuel combustion compared to 2011, bringing U.S. CO2 emissions to nearly 12 percent below 2005 levels. President Obama has committed to reduce global warming pollution 17 percent below the 2005 benchmark by 2020.


By now many commentators have noted that low natural gas prices have reduced power plant pollution as gas-fired generation has replaced higher-emitting coal-fired power. Indeed in April 2012 generation from natural gas equaled generation from coal for the first time since EIA started keeping track in 1973. For the year as a whole coal supplied less than 40 percent of our electricity and natural gas supplied more than 30 percent for the first time in EIA’s records.

Replacing coal with natural gas reduces smokestack emissions of CO2, SO2, and mercury, but natural gas production and distribution comes with a host of problems, including methane leaks, contaminated water supplies, destroyed streams and devastated landscapes; and while gas-fired power plants have lower CO2 emissions than coal-fired ones, their emissions are still far too high to be considered a global warming solution. Fortunately, there is a lot more behind the decline in U.S. CO2 emissions.

Sticking with the power sector for the moment, energy efficiency has also played a crucial role. EIA’s data show that total electricity generation in 2012 was more than 1 percent lower than in 2011 and virtually identical to 2005 levels. Meanwhile real (inflation-adjusted) GDP grew by 2.2 percent last year and was 7.7 percent higher than in 2005. At the same time there was a significant increase in generation from renewable energy sources, particularly wind, which produced 3.5 percent of total net generation in 2012 compared with 2.9 percent in 2011 and 0.4 percent in 2005.

Emissions from the transportation sector are also declining. Overall CO2 emissions from burning oil for transportation fell 2.2 percent in 2012 compared to 2011 and were 9.3 percent below 2005 levels. While the amounts varied, there were reductions from each of the major contributors to transportation-sector emissions: gasoline, diesel, and jet fuel. These reductions are due to a combination of increases in vehicle efficiency and reductions in driving. EPA data show that CO2 emissions from new passenger vehicles fell to 374 grams per mile (g/mi) in 2012, a 6 percent reduction since 2011 and a remarkable 16 percent reduction since 2005. Of course the efficiency of the vehicle fleet as a whole lags behind the new car levels. My colleague Luke Tonachel estimates that the fleet-wide emission rate has declined by about 3 percent since 2005 while total driving has declined slightly; meanwhile EIA data show that ethanol use has increased from 1.2 percent to 4.3 percent of transportation energy consumption (EIA treats ethanol combustion as if it were carbon neutral even though the lifecycle emissions from producing and using ethanol can be higher than from gasoline).

Another way to look at the contributors to the observed reduction in U.S. CO2 emissions is to compare what actually happened to a scenario of what would have happened if there hadn’t been a recession, a shift in energy sources, or improvements in energy efficiency. The Council of Economic Advisors performed such an analysis, which is included in the 2013 Economic Report of the President.  This analysis finds that 2012 emissions were 17 percent below the business-as-usual baseline constructed by CEA (as opposed to 12 percent below actual 2005 emissions). CEA concludes that 52 percent of this reduction is due to the recession, 40 percent due to cleaner fuels, and 8 percent due to accelerated improvements in energy efficiency (see figure). Note that this decomposition significantly under-states the overall role of energy efficiency because CEA only counted the acceleration of energy efficiency improvements relative to their business-as-usual forecast, which already assumed that energy use per dollar of GDP would fall by 1.6 percent per year.


Of course, the most important remaining question is can the U.S. continue to reduce its carbon dioxide emissions in the future to achieve the president’s 2020 goal of a 17 percent reduction from 2005 levels, and eventually the 80 percent or more reductions needed to prevent the most dangerous risks of climate disruption. As I have noted before, this target is within reach, but additional policies, particularly power plant carbon pollution standards will be needed. The president’s science advisors have presented a great 6-point plan for achieving this goal.

In the near-term, however, don’t be surprised if emissions increase this year. EIA’s Short-Term Energy Outlook forecasts almost a 2 percent jump in CO2 emissions, mostly from increased coal combustion as natural gas prices rise. To prevent that, and to sustain the rate of progress we have seen in recent years, we will need to redouble clean-energy efforts at all levels: Federal carbon and energy efficiency standards, state renewable energy, energy efficiency, and transportation policies, and local organizing to replace dirty coal plants with clean alternatives.

We can build the clean energy future we need, but we aren’t there yet and it’s not going to happen by itself.

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Andrew ShepardApr 9 2013 03:54 PM

Today's Senate Armed Services Committee hearing with US Pacific fleet commander Adm. Samuel Locklear, around 10:10 AM on C-SPAN:

Senator James "The Hoax" Inhofe tried in vain to compel the admiral to retract a previous statement the officer had made on the danger of global warming, particularly as regards littoral states that are of concern to the US military. After a couple of minutes (during which the admiral, who seemed not to realize that Inhofe is the Senate's premier climate crank, had repeated the scientifically uncontroversial fact) the senator, struggling to contain his impotent rage and frustration that the commander was failing to drink the denial kool-aid quickly wrapped up this line of questioning by accusing him of "using up half" of "his" time, testily switching to more mundane and technical policy questions.

William reillyApr 12 2013 09:37 AM

Very good piece Dan. Well done!

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