Total U.S. carbon emissions peaked during the mid 2000’s.  The reduction of carbon emissions has been attributed to factors such as the recent large expansions of wind and solar power.  Other factors that have also significantly reduced U.S. carbon emissions since 2005 are energy efficiency increases, expanded biofuels and replacing coal with natural gas.  While renewable energy and biofuels are strongly supported by State and Federal Governments, the recent boom in natural gas production from shale reserves has faced increasing criticisms and growing political opposition. 

For the U.S. to substantially reduce its future carbon emissions, higher carbon intensity coal and petroleum fossil fuels must to be replaced with lower carbon alternatives.  Besides further increasing renewables energy supplies and increasing energy efficiency, can U.S. total carbon emissions be substantially reduced without increased lower carbon natural gas? 

Brief History of U.S. Carbon Emissions – the generation of carbon emissions from the consumption of fossil fuels has generally increased in tandem with the overall population and the economy’s growth.  Refer to the following graph.


Source: EIA MER data Table 12.1

Between 1981 and 2005 the U.S. total population increased from 230 to 295 million and the total national GDP doubled.  Total U.S. carbon emissions increased from 4,500 to 6,000 million metric tons per year (MMT/yr.) during the same period.  Due to the oil crises of the 1970’s-early 1980’s the U.S. implemented many regulations intended to replace petroleum oil with alternatives fuels and supported-mandated energy efficiency increases.  Petroleum alternatives included alcohols, LPG, natural gas and electricity.  Over the past decade, State and Federal Governments have increasingly supported different renewable energy sources including biomass and wind/solar power, and further increases in energy efficiency.  All of these petroleum alternatives and efficiency improvements helped lead to peaking of total U.S. carbon emissions and very significant reductions since 2005.

Other factors that have significantly contributed to reduced U.S. carbon emissions are the recent new growth in domestic natural gas production-consumption and EPA regulations that have restricted new coal power plant construction.  The rapid increase in domestic natural gas production from shale reserves has significantly impacted the economics of coal fuels used for power and heat in recent years.  This recent shale natural gas boom has not only reversed the depletion trend of conventional natural gas production from a few years ago, but has actually flooded markets supplies.  This has caused natural gas price declines towards (inflation adjusted) historic lows.  These factors have made coal-to-natural gas ‘fuels switching’ very economically attractive to the Power and Industrial sectors.

Factors That Have Affected Recent U.S. End-use Sectors’ Carbon Emissions – Total U.S. carbon emissions recently peaked due to the combination of Government energy policies and free market factors.  Since 2005 the consumption of higher carbon fossil fuels has begun to decline very significantly, which has caused individual U.S. end-use Sectors’ carbon emissions to also decline.  Refer to the following graph.


Source: EIA MER data Tables 12.1 thru 12.6.  Carbon emissions based on ‘primary energy’ consumption only.

The carbon emissions of all end-use Sectors have decreased since 2005.  The largest reductions appear to be due to the Electric Power and Transportation sector’s emissions, followed by the Industrial, Residential and Commercial sectors. 

AllU.S. end-use Sectors’ carbon emissions have been impacted by a broad range of factors.  These include expanding renewable energy, increasing efficiency, and replacing coal with lower carbon alternatives.  The following summarizes some of the most significant factors which have successfully reduced carbon emissions in each end-use Sector 2005-2012:

  • Residential – natural gas and petroleum heating oil consumption has declined significantly.  These fossil fuels have been replaced by geothermal and electric heat pumps, and reduced by a large increase in residences’ thermal efficiencies; increased insulation and appliance efficiencies.  Distributed solar PV has also increased.
  • Commercial – coal and petroleum heating oil consumption has declined significantly.  Reduced consumption is largely due to energy efficiency increases.  One of the largest improvements has been a very significant increase in biomass based energy used for heat and distributed power generation.  In addition the use of geothermal heat systems has expanded significantly.
  • Industrial – petroleum and coal consumption has declined very significantly.  This has been due to large energy efficiency increases across most Industries and ‘fuels switching’ from coal and petroleum to natural gas.  Significant increases of biomass energy have also reduced the need for fossil fuels.
  • Transportation – petroleum motor fuels consumption has very significantly decreased due to increasing CAFE (fuel efficiency) standards.  The expansion of liquid biofuels has also significantly reduced petroleum consumption.  The replacement of petroleum with alternative natural gas fuels has made a small contribution towards total reduced carbon emissions.  The impact of electric vehicles has surprisingly been relatively insignificant.
  • Power – the largest reduction to carbon emissions is due to coal-to-natural gas ‘fuels switching’ and construction of higher efficiency power plants.  Expansion of renewable power, overwhelmingly due to expanded wind power, has been the second largest factor to reduced Power Sector carbon emissions. 

Another general factor that has affected overall end-use Sectors and markets fossil fuels use has been a change of Consumer behavior.  Beside the impacts of the recent economic recession (high unemployment and reduced income), Consumer concerns for the environment has also possibly reduced fossil fuels consumption and increased energy efficiency.

Innovative Technologies Impact on Carbon Emissions – there is no question that innovation and creative improvements have contributed substantially to renewable energy development and expansions.  Significant improvements have also contributed to the thermal efficiency and carbon emission reductions of replacing coal with state-of-art natural gas power generation technology.  The largest improvement has been upgrading older basic and relatively inefficient fossil fuels fired boilers & steam turbine generators with state-of-art combined cycle natural gas (CCNG) turbine power generation plants.  To illustrate refer to the following graph.


Source: EIA MER data Tables 2.6 and 7.2b.  The energy efficiency is estimated based on the unit heat:power value of 3413 Btu per KWH.

The above graph shows the significant difference between average U.S. CCNG and coal power plant efficiencies.  Since about 2000 the penetration of CCNG power plants has grown quite substantially.  The efficiency of conventional coal power plants has remained relatively constant until recent years.  Increasingly strict environmental regulations, which have required installation of emissions controls, have slightly decreased average coal power plant energy efficiencies.

In addition to thermal efficiency another factor that affects the reduction in carbon emissions of coal-to-natural gas ‘fuels switching’ are the physical ‘carbon factors’.  The EIA carbon factors for coal and natural gas are 95 and 53 kgCO2/MBtu respectively.  The combination of carbon factors and thermal efficiency has contributed to the carbon emissions differences per unit power generation of coal & natural gas.  Refer to the following graph.


Source: EIA MER data Tables 12.6 and 7.2b.  Note: NG – natural gas

The carbon emissions of average conventional coal power plants are now over twice that of natural gas power plants per KWH.  The combination of increased efficiency and reduced fuel costs have been major factors to the rapid replacement of coal with natural gas in recent years. 

Major Contributing Factors to Actual U.S. Carbon Emission Reductions – U.S. carbon emissions from the consumption of fossil fuels have declined by 700 MMT/yr. since 2005.  The reduction of carbon emissions has been due to four primary factors: 1) Improved Energy Efficiency, 2) Coal-to-Natural Gas Fuels Switching, 3) Increased Renewable Power + Heat, and, 4) Increased Liquid Biofuels.   Based on my detailed analysis of each end-use Sector’s energy consumption, the following table was developed to show the four different carbon emission reduction categories’ impacts on reducing U.S. carbon emissions 2005-2012.


Source: EIA MER data Tables 2.2-2.6 and Tables 12.2-12.6.  Note: Power sector natural gas efficiency+carbon factor impacts are classified as coal-to-NG fuel switching only since these are dependent variables.  Liquid biofuels impact is based on 20% average carbon emission reduction of the full lifecycle balances per the EISA 2007 standard for conventional ethanol.

The above table shows that 50% of the total reduced U.S. carbon emissions over the past 7 years are due to reduced Electric Power sector’s emissions.  This improvement resulted at nearly constant total U.S. power generation rates between 2005 and 2012.  The second largest (22%) reduction in U.S. carbon emissions is due to improvements in the Transportation sector, followed by the Industrial sector (18%). 

The table also shows that coal-to-natural gas ‘fuels switching’ is the largest contributing factor category (47%) towards reduced total U.S. carbon emissions 2005-2012.  The second largest contributing factor is increased ‘energy efficiency’.  Although renewable power/energy and biofuels have been very strongly supported and have increased significantly, these two factors have only contributed to 12% and 2% respectively towards total reduced U.S. carbon emissions over the past 7 years. 

U.S. Carbon Emissions Without Natural Gas – without the contribution of coal-to-natural gas ‘fuels switching’ over the past 7 years total U.S. carbon emissions could have increased up to 328 MMT/yr., or the costs of electric power and natural gas heating fuels would have increased substantially.  If the recent boom in domestic shale (natural) gas had not occurred or was not allowed to develop, the U.S. would have been forced to import increasing and substantial amounts of liquefied natural gas (LNG) after about 2005.  Without shale gas U.S. conventional natural gas production would have continued to deplete well below domestic demand levels.  Importing LNG to meet growing demand could have increased natural gas heating and power costs by over double current retail market prices.

Renewable energy development would have also been affected significantly without increased shale gas.  Variable wind and solar power cannot displace baseload coal power directly and requires 100% intermediate-peaking natural gas backup power in order to reliably supply existing power grids.  Without natural gas power backup, increasing levels of variable wind/solar power would compromise power grid stabilities-reliabilities (i.e. increased black-outs).  Biofuels also consumes significant amounts of natural gas during overall lifecycle cultivation-through-production & distribution.  Only hydro, biomass and geothermal renewable power sources or nuclear power can feasibly replace coal power directly without the need for natural gas backup.

With the recent and planned EPA regulations that make new and many existing coal power plants uneconomical, the U.S. will be required to displace this critical baseload power capacity by either importing increasing amounts of LNG and/or substantially expanding all non-coal power sources, other than variable wind and solar power.

Feasible Reductions of Future U.S. Carbon Emissions – significantly reducing U.S. total future carbon emissions will require a Federal ‘energy policy’ that builds on the successes of recent years.  This should include not only continued increases in energy efficiency and further development of reasonably cost effective renewable energy, but also, new support for current-future shale gas production.  Until the U.S. either substantially expands hydroelectric power and associated pumped storage or realistically develops alternative Industrial scale electric power storage, expanded renewable wind and solar will continue to require essentially 100% CCNG power backup.

To comply with current and future EPA regulations that will prevent new construction and likely shutdown significant existing coal power plants, this capacity must be replaced by either baseload renewable power (geothermal, biomass or hydropower), expanded nuclear power, and/or increased CCNG power capacity.  Of these feasible alternatives to existing coal power, new CCNG power plant capacity is currently the most cost effective.  To ensure that the needed domestic shale gas supplies are available to meet future growing U.S. demand the Federal Government needs to change its current strategies towards the Natural Gas Industry and the developing hydraulic fracturing technology.  Rather than just putting up barriers to current and future shale gas development, the Federal Government needs to work with the Natural Gas Industry and help facilitate the development of critical domestic natural gas supplies in an environmentally responsible manner.  Only through a cooperative partnership between the responsible Federal Agencies and the Natural Gas Industries will the U.S. be capable of making the greatest progress towards reducing total future carbon emissions and ensuring the critically needed natural gas supplies are available during the interim until alternative renewable energy supplies are truly capable of replacing the need for all fossil fuels.