Carbon Footprint

A carbon footprint is defined as the total amount of carbon dioxide (CO2) and other greenhouse gases (GHGs) such as methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) that are emitted directly and indirectly from 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 created by everyday activities. For example, when a living space is heated with oil, gas, coal, or electricity, a certain amount of CO2 is emitted. In addition, when consumer items are sold in a store, the production, transportation, and packaging of these products also create a certain amount of CO2 and other GHGs. A carbon footprint is the sum of the total amount of CO2 produced by human activities in a given time frame (typically one year). 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 GHGs humans are producing, it is also a way to understand the chemical nature these substances have in different parts of the atmosphere. The creation of CO2 and other GHG molecules from the burning of fossil fuels have different chemical behaviors than their original fossil fuel molecules. Many GHG 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 UV radiation; however, 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.

Determining the Source and Impact

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 (fuel used for international aviation and maritime transportation), 4 percent; and cement production, 3 percent. The most common human activity that produces an abundance of CO2 in the atmosphere is burning liquid fuels in automobiles.

Other GHGs produced from the burning of liquid fuel in engines include, but are not limited to, methane and ozone gas (CH4 and O3, respectively). One method for estimating the amount of CO2 and other GHGs 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 combined in order to determine the individual, household, city, state, nation, or total global carbon footprint. Human activities on the entire planet produce approximately 27,500 million tons of CO2 annually. In 2006, China surpassed the United States as the number one emitter of CO2, with 6,200 million tons annually. The U.S. emissions of CO2 was 5,800 million tons, according to the Netherlands Environmental Assessment Agency. However, on a per-capita basis, the average Chinese citizen is responsible for 10,500 lb. (4,763 kg) of CO2, while the average U.S. citizen is responsible for 42,500 lb. (19,278 kg) as a result of driving, traveling by airplane, heating and electricity for a living space, and purchasing manufactured products.

There are a significant number of online carbonfootprint calculator tools available, ranging from the very basic to the very complex, which demonstrates an increased public awareness and interest in understanding how individuals, groups, and/or countries utilize carbon-based resources. Most of these tools provide a basic snapshot of an individual’s carbon footprint. A typical basic carbon footprint example is Yahoo Green: Your Carbon Footprint. A more comprehensive example of an individual/household footprint can be found with the Carbon Footprint Calculator, which covers consumption of energy, flights, transportation, lifestyle, and food preference. Businesses can use the TerraPass Carbon Balanced Business program. For a country-by-country comparison, the researchers at the Norwegian University of Science and Technology and the Centre of International Climate and Environment Research in Oslo have created a detailed country footprint that includes countries’ transportation and manufactured goods.

There are a number of groups and organizations working to create a more scientifically literate population as well as propose and implement programs and policies that reduce CO2 and other GHGs. The Clean Development Mechanism (CDM), a provision in the Kyoto Protocol, is an offset that allows more developed countries to invest in lower emissions-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 (by using public transportation or bicycles), reduce household heating by a couple of degrees, purchase green energy, plant a tree, recycle, and buy products with reduced packaging.