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Report: Can U.S. Carbon Emissions Keep Falling?

Research Report by Climate Central

Report Summary

A Climate Central analysis of the American energy economy shows that the nearly 9 percent reduction in annual carbon emissions in the U.S. since 2005 is unlikely to continue in the years ahead without major departures from the ways energy is currently produced and used.

The upper line shows U.S. energy-related CO2 emissions projected in the AEO Extended Policies scenario (EIA, 2012b). The additional lines describe a hypothetical alternative scenario involving aggressive expansion of natural gas power generation, coal with CO2 capture and storage, expanded renewable electricity, and/or reduced vehicle-miles traveled.
Click image to enlarge.

Recent declines in carbon emissions are the result of a combination of factors including the recession, increased natural gas production and the related decline in coal-fired electricity generation, continuing improvements in efficiencies of energy use, and growth in renewables, particularly wind power. The recession, however, appears to be the most significant factor in the decline.

Consequently, as the economy rebounds the fall in emissions is likely to be neutralized or overtaken by growing population and incomes that will drive increased demand for energy-using appliances, air conditioners, TVs, personal electronic devices, cars, and other amenities. In the face of such growth and the 80 percent reliance of the U.S. on fossil fuels for energy today, modest improvements in energy efficiencies and expansions of lower-carbon energy alternatives will not provide the level of change in the energy economy needed for carbon emissions to fall by 2050 to a level that most climate scientists believe is needed to avoid severe impacts of climate change.

Key findings


  • Recent reductions in coal-generated electricity, driven primarily by extremely low natural gas prices, have left the existing U.S. fleet of coal-fired power plants operating at only about 50 percent capacity. Gas prices will not remain at historic lows, however, and eventual price increases will make firing up idle coal capacity more competitive, leading to increased CO2 emissions. 
  • Doubling new car MPG by 2025 will produce about a 40 percent reduction in overall fleet gasoline consumption but not more than this since new cars are a small fraction of the total fleet. This 40 percent reduction assumes that the total number of vehicle miles driven by a growing population will be no higher than today, which is unlikely. Historically, increases in total miles driven have more than offset increases in car and light truck MPGs, resulting in increased gasoline consumption and carbon emissions.
  • If the following hypothetical energy-related changes occur in the U.S. between now and 2035:

- the total number of miles driven by cars and light trucks stays constant at today’s level while the average MPG for new cars increases to over 55 MPG in 2035,

- gains continue to be made in the efficiencies of residential, commercial, and industrial energy-using equipment, 

- the share of natural gas electricity ramps up from 29 percent today to 44 percent in 2035, with a corresponding reduction to 18 percent in coal’s share,

- all coal-fired power plants in 2035 are operated with CO2 capture and storage or alternatively, renewables grow from 5 percent of electricity today to 31 percent by 2035, replacing coal;

then U.S. CO2 emissions in 2035 will decline to 38 percent below the 2005 level. Most climate scientists believe that emission reductions of at least 80 percent of the 2005 level will be needed in the U.S. and other industrialized countries by 2050 to avoid the most dangerous impacts of climate change. 


By Dave (Basking Ridge, NJ 07920)
on October 2nd, 2012

With all due respect I think that the graph shown here is deceptive in detail and that the message here sidesteps the point. For instance, the actual data that I have seen from the EPA and UNFCCC indicates that US emissions (CO2 from energy) did indeed fall largely due to the recession but then from 2009 to 2010 there was an increase in US CO2 emissions - about 3%.  In 2011 perhaps it dropped back again. Certainly also you have to be careful with the numbers here. There is data for CO2 emissions and then there is data for CO2 eqivalent emissions and data also that takes into account land efffects and so on.  So it can be a chore finding data sets that are apples to apples.

Still, regardless of all that I think that the key thing to keep in mind is that it is quite clear that US GHG emissions are still significantly above 1990 levels.

“Since 1990, U.S. greenhouse gas emissions have increased by 10.5%”, (EPA - 2010). UNFCCC Data - CO2 from energy 1990 to 2010 increase was 13.3%; The latter reference may be especially interesting.  There is a world map and a table which compares emissions changes according to country (annex 1) and breaks the data down. You can also see there that the EU (27) emissions are well below 1990 levels.  I think this is because most major EU countries have national energy and climate change policies.  As we all know, the US does not.  So, having looked through the report discussed here, I personally find it incomplete in so far as I think it is an important omission not to also compare or at least reference the performance of other countries.

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By Mukund Bangalore (London, United Kingdom)
on October 3rd, 2012

According to the EPA’s GHG Inventory (, in 2010, U.S. greenhouse gas emissions totaled 6.8 million metric tons CO2 Eq. Just curious -  why wasn’t the GHG Inventory used as a basis for estimating carbon emissions?

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By maxwells
on October 3rd, 2012

Methane has 1/2 the carbon footprint of coal. But the shift from coal to natural gas use depends largely on FRACKING technology, with ~2-4% uncaptured methane emissions, due to leaks from ground cracking (Howarth et al.,) Rising methane levels since 2007 seem consistent with such increased fugitive emissions.

And methane has ~20 to 25 times the global warming potential (GWP) of CO2.

IF so, as long as major fracking cotninues, THEN the bottom line on whether natural gas use is cleaner than coal is whether

( 20 - 25 ) x ( 0.02 - 0.04 ) is less than 1/2.

The range estimate appears to be from 0.4 (slightly better) to 1.0 (much worse).

What this seems to say is that the shift to “cleaner” natural gas is at best a temporary and largely cosmetic band-aid and at worst a chimera that masks a more rapidly deteriorating situation.

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By kap55 (Minneapolis, MN)
on October 3rd, 2012

So this report concludes that basically, we are on a completely unsustainable path regarding carbon emissions, regardless of how we proceed ... but oddly enough, NOT ONE MENTION of the best long-term carbon-free solution, nuclear energy.

Let’s be clear: we can NEVER get off fossil fuels unless the rate of growth & installation of carbon-free energy exceeds the growth in global GDP. Solar is pathetic in terms of cost and availability. Wind and nuclear are it.

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By Eric Larson
on October 3rd, 2012

Dave and Mukund: Thanks for your careful observations and comments, to which I will offer a combined response. Figure 1 in our report does, indeed, show U.S. energy-related CO2 emissions increased from 2009 to 2010, and that they dropped again the following year, which seems consistent with the EPA CO2eq numbers you have mentioned. We chose to report only energy-related CO2 (not CO2eq) because that is the source of GHGs that dominates the total and thus provided a simpler way to discuss trends and illustrate possible future pathways than if we had included all of the many additional non-CO2 sources that make up total GHG emissions. On the other hand, I agree with you it would be more complete if we were to include all GHGs in our analysis. Dave, your point that U.S. emissions are still above 1990 levels is well taken. For better or worse, 2005 seems to have become the default reference year in many of the prominent discussions on carbon so we have used 2005 as a reference.  And finally, a comparison between the historical US emissions trajectory and that for the EU 27 would be very interesting, but a bit outside the main thrust of this report. I will save that idea for a future analysis.

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By Tamara
on October 3rd, 2012

A central assumption of this article is that the economy will inevitably rebound.  That is not necessarily a given.  The increasingly frantic pursuit of economic growth via the inflation of more and more bubbles of imaginary money cannot continue forever.

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