A carbon footprint is an estimate of the greenhouse gases caused by an activity, product, person, company, or country. It is usually expressed as carbon dioxide equivalent, written as CO2e, because different gases can warm the atmosphere at different strengths. CO2e turns them into one comparison number.
Many everyday actions have a carbon footprint. Driving a car, heating a home, flying, producing food, manufacturing electronics, shipping products, and running data centers all use energy or materials. Some emissions are direct, such as fuel burned in a car. Others are indirect, such as electricity used to make a product in a factory.
A product's footprint can include many stages: raw materials, manufacturing, transport, use, and disposal. For example, a laptop has emissions from mining materials, producing parts, assembling the device, shipping it, charging it, and eventually recycling or discarding it.
The purpose of measuring a carbon footprint is not only to attach a number. It helps identify where changes may matter most. A household may reduce energy use, choose efficient appliances, repair items, reduce waste, or use cleaner transport. A company may improve supply chains, energy sources, packaging, and logistics.
A carbon footprint is an estimate, so methods and assumptions matter. Still, it is a useful way to think about the hidden climate impact of choices that otherwise feel disconnected from energy and emissions.