Carbon footprint is a measure of the amount of greenhouse gases released by human activities. Greenhouse gases trap heat in Earth’s atmosphere, much like the glass walls of a greenhouse. Many human activities release carbon dioxide and methane—two greenhouse gases—into the atmosphere. Most scientists think that the release of such gases by human activity has contributed to global warming. Global warming is a potentially harmful increase in Earth’s average temperature (see Global warming). The carbon footprint of a particular activity or lifestyle measures the release of greenhouse gases connected with it.
A carbon footprint has two parts: a primary footprint and a secondary footprint. The primary footprint measures the emissions caused directly. For example, the primary footprint of driving a car includes greenhouse gases emitted by the car’s engine. The footprint would depend on the distance traveled, the car’s fuel efficiency, and whether the driver carpooled.
A secondary carbon footprint measures the greenhouse gases that go into the manufacture and maintenance of products people use or buy. For example, wearing shoes does not directly result in greenhouse gas emissions. But such gases are emitted in the manufacture and transport of shoes. Different products have different secondary footprints. For example, leather sneakers made in China and sold in the United States have a different secondary footprint than plastic sandals made in the United States.
Businesses and other organizations also have primary and secondary carbon footprints. Special surveys called carbon footprint calculators help people and organizations to estimate the release of greenhouse gases as a result of their activities and choices.
