Carbon Footprint

A CARBON FOOTpRINT is defined as the total amount of carbon dioxide (CO2) and other greenhouse gases such as methane (CH4), nitrous oxide (N2O), hydro-fluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) emitted directly and indirectly to support human activities such as the burning of fossil fuels, deforestation, livestock raising, and agricultural production. Calculating a carbon footprint is a tool for understanding the amount of global warming gases everyday activities create. For example, when heating a living space with oil, gas, coal, or electricity, a certain amount of CO2 is emitted. In addition, when buying consumer items from a store, the production, transportation, and packaging of these products also create a certain amount of CO2 and other greenhouse gases. A carbon footprint is the sum of the total amount of CO2 produced by human activities in a given time frame (typically a year's time). Carbon footprints are generally expressed in annual tons of CO2.

The carbon footprint is not only a method of estimating the amount of CO2 and greenhouse gases humans are producing, but a way to understand the chemical nature these substances have in different parts of the atmosphere. CO2 and other greenhouse gas molecules created from the burning of fossil fuels have different chemical behaviors than their original fossil fuel molecules. Many greenhouse gas molecules produced from human activities accumulate in parts of the atmosphere where they have an undesirable effect. For example, the production of ozone gas (O3) is desirable in the stratosphere (upper atmosphere) where it protects humans from harmful ultraviolet radiation; however, production of an abundance of O3 in the troposphere (closer to where humans live) is undesirable because it acts as a lung irritant for people with respiratory illnesses (such as emphysema, asthma, and chronic bronchial inflammatory diseases), and contributes to smog production.

The largest sources of CO2 from the burning of fossil fuels are: liquid fuels (such as gasoline or diesel), 36 percent; solid fuels (such as coal and wood), 35 percent; gaseous fuels (such as natural gas), 20 percent; international bunkers, four percent; and cement production, 3 percent, according to research by M.R. Raupach. The most common human activity that produces an abundance of CO2 in the atmosphere is the use of liquid fuels in driving an automobile. Other greenhouse gases that are produced from the burning of liquid fuel in engines include, but are not limited to, methane and ozone gas (CH4 and O3).

One method for estimating the amount of CO2 and other greenhouse gases produced by human activities is determined from a balanced chemical equation (for example, stoichiometry) and then converted to an equivalent amount of CO2, which allows it to be added together to determine an individual, household, city, state, national, or total global carbon footprint. Human activities on the entire planet produce approximately 27,500 million tons of CO2 annually.

In 2006, China passed the United States as the number one emitter of CO2 with 6,200 million tons annually. The United State's emission of CO2 was 5,800 million tons, according to the Netherlands Environmental Assessment Agency. However, in a per person comparison, the average Chinese citizen is responsible for 10,500 pounds or 4,763 kilograms of CO2, while the average U.S. citizen is responsible for 42,500 pounds or 19,278 kilograms of CO2 as a result of heating and electricity for living spaces, driving, traveling by airplane, and purchasing manufactured products.

There are a number of groups and organizations working to create a more scientifically literate population and proposing and implementing programs and policies that reduce CO2 and other greenhouse gases. A provision in the Kyoto Protocol is the Clean Development Mechanism (CDM), which is an offset that allows more developed countries to invest in lower emission-producing facilities in developing or less-developed countries to avoid reducing emissions in their home countries.

Another proposal is a carbon tax, or the taxation of burning fossil fuels (such as liquid, solid, and gaseous fuels) to reduce CO2 emissions. Some groups are proposing a carbon label, where consumer products would report their carbon footprint on the label. Other practical methods for reducing carbon footprints are to reduce driving (for example, to use public transportation or bikes), reduce household heating by a couple of degrees, purchase green energy, plant a tree, recycle, and buy products with reduced packaging.

SEE ALSO: Carbon Cycle; Carbon Dioxide; Carbon Emissions; Carbon Permits; Public Awareness.

BIBLIOGRApHY. Netherlands Environmental Assessment Agency, "Chinese CO2 Emissions in Perspective," www.mnp.nl (cited July 2007); M.R. Raupach et al., "Global and Regional Drivers of Accelerating CO2 Emissions," PNAS (v.104, 2007); Thomas Wiedmann and Jan Minx, "A Definition of Carbon Footprint: ISA-UK Research Report 07-01" www.isa-research.co.uk (cited June 2007).

Andrew Hund, Ph.D University of Alaska, Anchorage

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