The document discusses the concept of carbon footprint, which is defined as the total greenhouse gas emissions caused by an individual, organization, product, etc. It notes that while the total carbon footprint is difficult to calculate precisely, experts have suggested measuring the amount of carbon dioxide and methane emissions from a population or activity. Common sources of carbon emissions include transportation, land use changes, and production and consumption of food. The carbon footprint is often expressed in terms of the carbon dioxide equivalent emitted.