U.S. Energy Information Administration - EIA - Independent Statistics and Analysis
U.S. Energy-Related Carbon Dioxide Emissions, 2015
Release Date: March 16, 2017 | Next Release Date: December 2017 | full report
U.S. Energy-related carbon dioxide emissions decreased 2.7% in 2015
Note: Unless otherwise indicated, all data in this analysis refer to the U.S. Energy Information Administration's (EIA) October 2016 Monthly Energy Review. Because of differing coverage and data vintage, percent changes may differ slightly with other EIA publications.
Natural gas carbon dioxide emissions almost matched those from coal in 2015
Of the four end-use sectors, only transportation emissions increased in 2015
The 2015 increase in energy-related carbon dioxide emissions from the transportation sector was led by motor gasoline
The 28% decrease in gasoline prices (in nominal dollars) from 2014 to 2015, along with the continued economic recovery, led to higher fuel consumption. Transportation-related CO2 emissions increased by 38 million metric tons (MMmt) (2.1%) in 2015.
Commercial sector energy-related carbon dioxide emissions declined in 2015
Commercial sector CO2 emissions declined by 53 MMmt (5.4%) in 2015, accounting for 36% of the total decrease in CO2 emissions.
Residential energy-related carbon dioxide emissions were lower in the last quarter of 2015 compared with recent years
Both 2012 and 2015 were warm years; however 2012 was very warm in the first quarter, 20% above normal as measured in heating degree days (HDD). While warmer than the first quarter of 2014, the first quarter of 2015 was close to normal. The last quarter of 2015 was particularly warm (also 20% warmer), and CO2 emissions reflected the lower use of fuel for heating.
Industrial sector energy-related carbon dioxide emissions declined from 2014 to 2015
The industrial sector's CO2 emissions, which fell by 4% (60 MMmt) in 2015, have remained essentially flat in recent years despite increasing output. Continuing growth in less energy-intensive output helped to stabilize emissions.
The increasing share of non-fossil fuel electricity generation has helped lower the carbon intensity of electricity supply
The trend of declining coal-fired electricity generation in the power sector and increasing non-fossil and natural gas-fired generation continued in 2015.
Growth in wind and solar electricity generation has supported the decreasing carbon intensity of the electricity supply
Although nuclear power remains the dominant source of non-fossil electricity generation, growth in wind and solar generation since 2008 has also contributed to a decline in the carbon intensity of electricity generation.
The decrease in energy-related carbon dioxide emissions in 2015 mainly reflected a decline in energy intensity
In 2015, the energy intensity of the U.S. economy declined by 3.4%. Over the previous decade, the average annual decline was 1.5%. Structural changes in the economy and weather fluctuations that affect energy use for heating and air conditioning can affect annual changes in energy intensity. CO2 emissions were 105 MMmt lower in 2015 than they would have been if energy intensity had declined by only 1.5% in 2015.
Increased use of natural gas and the growth in non-carbon generation has contributed to the decline in electric power sector* carbon intensity since 2005
*Note: includes data on distributed generation from U.S. Energy Information Administration, Monthly Energy Review, Table 10.6 Solar electricity net generation, October 2016.
Table 1 decomposes the rates of change by sector for electricity (indirect) and primary (direct) energy consumption and separates them from the changes in the respective carbon intensities. The sums of those changes multiplied by the share of CO2 emissions from each energy type approximates the sectoral changes in CO2 emissions.
Using the residential sector as an example, the drop in electricity consumed between 2014 and 2015 of 0.8% added to the decline in carbon intensity of the electricity supply (-5.1%) yields a total of -5.9% (not shown in the table). When -5.9% is multiplied by the electricity emissions share of 69.3%, the resulting electricity-weighted CO2 change is -4.1%. When this is added to the residential sector’s weighted change of primary energy (-2.4%) the result is the largest total sector change of -6.5%. Finally, when weighted by the residential share of total CO2 emissions (19.8%), the weighted sector share of -1.3% is about half the total change in energy-related CO2 emissions in 2015. In the commercial sector, the slight increase in electricity consumption somewhat offsets the drop in carbon intensity. Because energy use in the residential and commercial sectors is primarily electricity, their overall rate of CO2 change is largely determined by changes in power sector fuel consumption and the carbon intensity of the electricity supply. By contrast, the transportation sector is not significantly affected by electricity changes in 2015 and is almost totally dominated by primary energy consumption.
The industrial sector, while still dominated by primary energy consumption, has a large enough electricity share that large changes in electricity supply mix (as happened in 2015) can outweigh the relatively small change in primary energy consumption and produce a total sector change of -3.9%.When weighted by each sector's share of the total, as indicated above, the largest change in CO2 emissions (-1.3%) is in the residential sector. The industrial sector is the next largest contributor to the decline (-1.1%), followed by the commercial sector (-0.9%). The transportation sector’s growth offsets the total CO2 decline by +0.7%.
Future implications of the 2015 decline in carbon dioxide emissions
Specific circumstances, such as the very warm fourth quarter of 2015 and relatively low natural gas prices, put downward pressure on emissions as natural gas was substituted for coal in electricity generation. The downward pressure on emissions was slightly offset by an uptick in transportation energy consumption that was influenced by lower fuel prices that put upward pressure on emissions. These conditions do not necessarily reflect future trends.
For EIA's forecasts and projections on emissions and their key drivers, see the Short-Term Energy Outlook (STEO),with monthly forecasts through 2018 and the Annual Energy Outlook (AEO) with annual projections through 2050. EIA's International Energy Outlook (IEO) contains projections of international energy consumption and emissions through 2040. Full-length versions of the AEO and IEO are on a biennial schedule. Summary versions of these publications appear in alternating years.The analysis of energy-related CO2 emissions presented here is based on data in the Monthly Energy Review (MER). Chapter 12 of the MER reports monthly U.S. energy-related CO2 emissions derived from EIA’s monthly energy data. For the full range of EIA's emissions products, see the Environment webpage.
Terms used in this analysis:
British thermal unit(s) (Btu): The quantity of heat required to raise the temperature of 1 pound of liquid water by 1 degree Fahrenheit at the temperature at which water has its greatest density (approximately 39 degrees Fahrenheit).
Carbon intensity (economy): The amount of carbon by weight emitted per unit of economic activity. It is most commonly applied to the economy as a whole, where output is measured as the gross domestic product (GDP). The carbon intensity of the economy is the product of the energy intensity of the economy and the carbon intensity of the energy supply. Note: this value is currently expressed in the full weight of the carbon dioxide emitted (CO2/GDP).
Carbon intensity (energy supply): The amount of carbon by weight emitted per unit of energy consumed. A common measure of carbon intensity is weight of carbon per Btu of energy. When there is only one fossil fuel under consideration, the carbon intensity and the emissions coefficient are identical. When there are several fuels, carbon intensity is based on their combined emissions coefficients weighted by their energy consumption levels. Note: this value is currently measured in the full weight of the carbon dioxide emitted (CO2/energy or CO2/Btu).
Cooling degree days (CDD): A measure of how warm a location is over a period of time relative to a base temperature, most commonly specified as 65 degrees Fahrenheit. The measure is computed for each day by subtracting the base temperature (65 degrees) from the average of the day's high and low temperatures, with negative values set equal to zero. Each day's cooling degree days are summed to create a cooling-degree day measure for a specified reference period. Cooling degree days are used in energy analysis as an indicator of air conditioning energy requirements or use.
Energy intensity: A measure relating the output of an activity to the energy input to that activity. It is most commonly applied to the economy as a whole, where output is measured as the gross domestic product (GDP), and energy is measured in Btu to allow for the summing of all energy forms. On an economy-wide level, it is reflective of both energy efficiency as well as the structure of the economy. Economies in the process of industrializing tend to have higher energy intensities than economies that are in their post-industrial phase. The term energy intensity can also be used on a smaller scale to relate, for example, the amount of energy consumed in buildings to the amount of residential or commercial floor space.
Gross domestic product (GDP): The total value of goods and services produced by labor and property located in the United States. As long as the labor and property are located in the United States, the supplier (that is, the workers and, for property, the owners) may be either U.S. residents or residents of foreign countries.
Heating degree days (HDD):A measure of how cold a location is over a period of time relative to a base temperature, most commonly specified as 65 degrees Fahrenheit. The measure is computed for each day by subtracting the average of the day's high and low temperatures from the base temperature (65 degrees), with negative values set equal to zero. Each day's heating degree days are summed to create a heating-degree-day measure for a specified reference period. Heating degree days are used in energy analysis as an indicator of space heating energy requirements or use.
See the EIA glossary.
Methodology used in this analysis
With the exception of figures 10 and 11, the data in this report are directly from the published values in the MER or based on relatively simple calculations such as CO2/Btu of energy. The methodology of figures 10 and 11 is as follows:
Figure 10. The decrease compared to trend in energy-related carbon dioxide emissions in 2015 was due primarily to a decline in energy intensity: This figure gives context to the most recent year-to-year change by comparing it to the average change for key parameters over the previous decade. The key parameters are population, per capita GDP (GDP/population), energy intensity, and carbon intensity of the energy supply. The changes in these key parameters determine changes in energy-related carbon dioxide. By comparing the rate of change for each parameter from 2014 to 2015 to the average rate of change for that parameter for the previous decade, the contribution of each parameter towards the overall deviation from trend can be calculated. The table below summarizes the rates of change that drive the results. The larger the positive value, the greater the increase in emissions. The larger the negative value, the lesser the increase in emissions.
Figure 11. Increased use of natural gas and the growth in non-carbon generation have contributed to the decline in power sector carbon intensity since 2005: This figure shows the emissions savings from two factors that have allowed emissions to decrease from 2005 to 2015 while generation has risen slightly. The first factor is the shift within fossil fuel generation from coal to natural gas. To capture this shift, the fossil fuel carbon factor (fossil fuel CO2/fossil fuel generation) is frozen at the 2005 level. This factor is then multiplied by the actual fossil fuel generation for subsequent years. The difference between that value and the actual value for fossil fuel generated CO2 emissions is the savings in that year. For example, the carbon factor in 2005 for fossil fuel generation was 0.865 metric tons per megawatthour. By 2015 the carbon intensity had declined to 0.735 metric tons per megawatthour. Multiplying the 2005 value times the 2015 level of generation would yield 2,259 MMmt, versus the actual value of 1,919 MMmt. Therefore, the savings was 341 MMmt in 2015. Because non-carbon generation (the second factor) has a zero-carbon factor for direct emissions, the overall reduction in total carbon intensity was applied to total generation, i.e., multiplying total generation by the 2005 value of 0.619 metric tons per megawatthour. The savings in fossil fuel generation was subtracted from the total and the difference was credited to non-carbon generation. For example, the total savings in 2015 was 522, so the amount allocated to non-carbon generation is 522 minus 341 = 181.