Carbon emissions factors

Summary: Increasing concern about rising concentrations of greenhouse gases in the atmosphere has resulted in the need to identify the source of these emissions and to quantify them, allowing a carbon footprint to be calculated for any specific individual, event, product, or organization.

Calculating a carbon footprint requires a large amount of data that can be very difficult and time consuming to obtain, but the use of carbon emissions factors allows a reasonable estimate of a carbon footprint to be made from assessing emissions. The carbon footprint can be used to compare similar organizations, for instance, and also to identify carbon reduction strategies.

As an example, many colleges and universities in the United States have calculated their carbon footprint, which involves three separate categories. The first is direct emissions from a source owned or controlled by the institution, such as boilers used to heat campus buildings, vehicles owned by the institutions, releases of refrigerants or other greenhouse gases from refrigeration equipment, and can also include methane emissions from institution-owned farm animals. The second category is emissions related to electricity used by the campus produced from an outside source such as a local electric utility or merchant generator. The third category is broad and can include emissions from student and staff commuting to and from campus as well as institution-related business travel.

Other methodologies have been used by various companies to calculate similar data for their products and/or services, and many local and national governments also calculate carbon emissions.

Table 1 shows carbon emissions factors used by the U.S. Environmental Protection Agency. Other countries produce similar factors. In addition, the EPA also publishes carbon emissions factors for electric generation for each state and for individual plants, generally expressed as pounds of CO₂/MWh. Various methods are used to calculate carbon emissions, and the conversion factors in table 2 can be used to determine the desired units of measure (e.g., Carbon, CO₂).

Methods of reducing carbon emissions and global warming include increased energy efficiency, increased use of noncarbon-based energy sources, limiting economic growth, and the imposition of both voluntary and mandatory emissions controls by corporations, governments, or international agreements. Clean technologies such as carbon capture and storage or sequestration remove emissions before they are released into the atmosphere. An emerging and controversial practice is the growing market in carbon emissions trading, whereby countries or corporations trade carbon emissions to other countries or corporations with lower emissions rates in order to meet mandated carbon emissions limits.

Table 1. CO₂ Emission Factors by Fuel Type per Unit Volume, Mass, and Energy

Table 2. Carbon and CO₂ Conversions

Bibliography

Cowie, Jonathan. Climate Change: Biological and Human Aspects. New York: Cambridge University Press, 2007.

Smith, Adrian D. Toward Zero Carbon: The Chicago Central Area DeCarbonization Plan. Mulgrave, Victoria, Australia: Images Publishing Group, 2011.

United Nations Statistics Division. “CO₂ Emissions.” http://unstats.un.org/unsd/environment/air‗co2‗emissions.htm

U.S. Environmental Protection Agency. “Air Emissions/Clean Energy.” http://www.epa.gov/cleanenergy/energy-and-you/affect/air-emissions.html

Volk, Tyler. CO₂ Rising: The World’s Greatest Environmental Challenge. Cambridge, MA: MIT Press, 2008.