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U.S. Energy-Related Carbon Dioxide Emissions, 2010

Release Date: August 18, 2011   |  Next Release Date: August 2012  |  

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This analysis examines the level and drivers of energy-related carbon dioxide emissions in 2010. After a historic decline in 2009, energy-related carbon dioxide emissions rebounded in 2010, but still remain 358 million metric tons (6 percent) below the 2005 level.

What happened to carbon dioxide emissions from energy use in 2010?

In 2010, energy-related carbon dioxide emissions in the United States saw their largest absolute and percentage increase (213 million metric tons or 3.9 percent) since 1988 when they grew by 218 (4.6 percent). As shown below, only two years – 1996 and 2000 – have shown similar growth in the time period since 1990. However, unlike those years, 2010 was preceded by declines in three out of the four previous years. As will be discussed below, 2010 was an atypical year for emissions growth, just as 2009 showed an unusual decline.


How much of the 2010 emissions increase is related to a rebound in economic growth?

In 2009 the economy as measured by the real gross domestic product (GDP) fell by 3.5 percent compared to the previous year, but emissions fell by over 7 percent. In 2010 GDP grew by 3.0 percent, but emissions increased by 3.9 percent. While changes in emissions are highly correlated with economic activity, clearly there are additional factors that influence changes in emission levels. Since 1990, carbon dioxide emissions in the United States have grown much more slowly than GDP; in 2007 emissions reached a peak of about 20 percent greater than 1990, but even after the 2010 increase, carbon dioxide emissions are only about 12 percent greater. GDP has increased by 63 percent over that same time period.

Note: For a full definition of gross domestic product see the end of this analysis.


In addition to the economic rebound what factors caused the large increase in 2010 emissions?

Using the "Kaya Identity," changes in energy-related carbon dioxide can be understood in terms of the economy, the energy component of the economy and the carbon intensity of the fuel mix to meet the demand for energy. The total change in output is the sum of population growth (0.9 percent)1 and growth in per capita output (2.1 percent). In 2010 manufacturing industries showed a strong recovery from the 2008-9 recession and energy-intensive manufacturing experienced high growth as well. As a result energy intensity rose 0.7 percent.2 Additionally, because the industrial sector directly consumes coal and indirectly consumes electricity fueled heavily by coal, the carbon intensity of the energy supply increased by 0.1 percent.3 Also, a hot summer led to increased air-conditioning demand in the residential sector. The four factors: population (0.9 percent), output per capita (2.1 percent), energy intensity (0.7 percent), and carbon intensity (0.1 percent) combined to yield an emissions increase of 3.9 percent.4

1 Population growth in 2010 was estimated as 0.9 percent, the same growth rate as 2009.
2 Energy intensity is defined as energy consumed per unit of economic activity (Btu/GDP).
3 Carbon intensity of energy is defined as carbon dioxide emissions per unit of energy consumed (CO2/Btu).
4 Percent changes don't always exactly add up due to independent rounding and are an approximation of the actual changes in emissions.
For a full definition of Kaya Identity, energy intensity and carbon intensity see the end of this analysis.


Why did the energy intensity of the economy increase in 2010?

Total energy consumption rose by 3.8 percent in 2010 across all end-use* sectors. Because GDP increased by 3.0 percent, it meant that the energy intensity of the economy increased by 0.7 percent. The industrial sector experienced an increase in total energy consumption of 5.7 percent in 2010 - about two percentage points greater than overall energy demand. The residential sector total energy demand grew by 5.2 percent. Other sectors saw smaller increases-energy use in the transportation and commercial sectors grew by 1.9 percent and by 1.7 percent respectively.

Note: Total energy consumption includes both direct use of primary fuels and the energy value of primary fuels used to generate electricity consumed in each sector.
For a full definition of British thermal unit see the end of this analysis.


What drove demand growth in the industrial and residential sectors?

Primary (non-electrical) energy consumed in the industrial sector grew by 6.6 percent in 2010. The next largest increase was electrical energy demand in the residential sector (6.0 percent). The increase in primary energy in the industrial sector was largely the result of the rebound in manufacturing-up 5.8 percent from 2009 as measured by the manufacturing index. The electrical demand in the residential sector was the result of a 19 percent increase in cooling-degree days (CDDs) from 2009 as a very hot summer (CDDs 18 percent above normal) led to increased electricity demand to cool homes. The demand for industrial electricity, which has been either flat or declining in recent years also increased by 4.6 percent in 2010. Primary energy in the residential sector grew slightly less than overall energy demand -- 3.4 percent.

Note: Primary energy is that consumed directly in the sector. Electricity-related energy includes both the energy value of the electricity and losses from generation, transmission or distribution.
For a full definition of cooling degree-days and primary energy, see the end of this analysis.


Why did the carbon intensity of the energy supply increase in 2010?

After an unprecedented drop of 12 percent in 2009, coal consumption rose by almost 6 percent in 2010. This increase in coal consumption and related emissions contributed to a 0.1 percent increase in overall carbon intensity. While this is not a large increase per se, it should be seen in contrast to 2009 when the carbon intensity of the energy supply fell by over 2 percent.


How did the change in fuel supply mix in the electric power sector impact the carbon intensity of energy supply in 2010?

The electric power sector saw growth in demand of 4.2 percent in 2010, while emissions rose by 5.2 percent. This indicates an increase in the carbon intensity of electric power generation of about 0.9 percent. In 2010, coal generation grew by 90 billion kWh or 56 percent of the increase in generation. And because coal is the most carbon-intensive of fuels, this increased the overall carbon intensity of the electric power sector. The overall share of coal in total generation increased slightly from 45.7 percent in 2009 to 46.1 percent in 2010. The natural gas share of total generation rose from 22.1 percent in 2009 to 22.6 percent in 2010.


What happened to non-carbon options in 2010 electricity generation?

There is a mixed story in terms of the non-carbon generation options in 2010. The total category of non-carbon generation saw an increase of 1.2 percent. However, because total generation increased by 4.2 percent, it meant that the share of non-carbon generation fell from 30 percent to 29 percent. A large drop in hydropower generation offset much of the increase in nuclear and wind and solar. Wood generation saw only small increases. The result was that non-carbon generation sources increased less than 14 billion kWh.

Note: Although biomass-based renewable electricity generation emits carbon dioxide during combustion, this analysis assumes those emissions are offset through biological sequestration, resulting in net-zero emissions.


How did 2010 compare to the last several years on a month-by-month basis?

Total monthly emissions show some seasonality with peaks at the beginning and end of each year. There is also a summer peak but at a lower level than the winter peaks. One thing that is noticeable is that the 2008 monthly values show both the seasonal weather effects as well as the economic downturn. The first half of the year saw positive economic growth, while the second half of the year began to show the economic slowdown. The slowdown continued throughout 2009.


Which end-use sector shows the most seasonality?

Residential sector emissions show distinct seasonal weather patterns. In addition to the economic downturn, 2009 experienced a relatively mild summer with less cooling-degree days than in 2008. The summer of 2010, on the other hand was much warmer than average. These factors can be seen in the emission patterns over the three years. The commercial sector shows some seasonality, but less than the residential sector.


What end-use sector is the least seasonal in its emissions patterns?

The industrial sector shows little seasonality as its energy use and emissions is largely determined by economic activity. This can be seen in the three years shown below. The economic downturn that began in 2008 is further reflected in 2009 where the emissions are at their lowest. In 2010, the recovery places energy usage and emissions above 2009 but below 2008. In December of 2010 emissions exceed both previous years. The transportation sector also does not show much seasonality despite the summer driving season, as fuels other than gasoline are consistently consumed throughout the year.


Does the electric power sector exhibit seasonality in its emissions patterns?

The electric power sector exhibits strong seasonality with a summer peak tied to cooling requirements and smaller winter peaks corresponding to demand for electric heating. The very warm summer of 2010 can be seen in the figure below where August of 2010 was the monthly emissions peak for the year.


What are the implications of the carbon dioxide emissions increase in 2010?

It is difficult to draw conclusions from one year of data. Just as 2009 was an atypical year in terms of the magnitude of the emissions decline, 2010 likely does not signal a new trend in emissions growth.

For EIA's projections on emissions and the factors that contribute to their underlying trends, see either our short-term forecast through 2012 that is updated monthly at www.eia.gov/steo, or longer-term projections through 2035 that are updated annually at www.eia.gov/aeo. EIA's projection of international energy consumption and emissions to 2035 can be found at http://www.eia.gov/oiaf/ieo/index.html.

Starting in the fall of 2010, the Energy Information Administration (EIA) expanded its reporting of energy-related carbon dioxide emissions in both the Monthly Energy Review (MER) and the Short-Term Energy Outlook (STEO). The MER now reports monthly energy-related carbon dioxide emissions derived from our monthly energy data, while the STEO now forecasts these emissions to accompany its traditional forecasts of energy use.

All the latest emissions data (including annual updates) can now be found in Chapter 12 of the Monthly Energy Review at www.eia.gov/mer.

For the full range of EIA's emissions products see: http://www.eia.gov/environment/

Terms used in this analysis:

British thermal unit: 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:The amount of carbon by weight emitted per unit of energy consumed. A common measure of carbon intensity is weight of carbon per British thermal unit (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.

Cooling degree-days (CDDs): 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 British Thermal Units (Btu) that 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.

Kaya Identity: An equation stating that total energy-related carbon dioxide emissions can be expressed as the product of four inputs: 1) population, 2) GDP (output) per capita, 3) energy use per unit of GDP, and 4) carbon emissions per unit of energy consumed.  The change in the four inputs can approximate the change in energy-related carbon dioxide.

Primary energy: Energy in the form that it is first accounted for in a statistical energy balance, before any transformation to secondary or tertiary forms of energy. For example, coal can be converted to synthetic gas, which can be converted to electricity; in this example, coal is primary energy, synthetic gas is secondary energy, and electricity is tertiary energy. In the context of this analysis it would mean energy consumed directly by a home, business or industrial operation as opposed to electricity generated elsewhere and supplied to the end-user.

For other definitions see the EIA glossary: http://www.eia.gov/tools/glossary/