TLDR: The carbon footprint is a way to measure the amount of greenhouse gases emitted from different activities, products, companies, or countries. It helps us compare the climate change impact of different things and make choices that are better for the environment.

The carbon footprint is a measure of the total amount of carbon dioxide (CO2) and other greenhouse gases emitted from a specific activity, product, company, or country. It is usually reported in tons of emissions per unit of comparison, such as per year, per person, or per kilogram of protein. For example, the carbon footprint of a product includes the emissions from its entire life cycle, from production to disposal. Similarly, for an organization, its carbon footprint includes both direct and indirect emissions caused by the organization.

There are different methods and tools available to calculate the carbon footprint, depending on the focus of the analysis. For example, there are calculators that help individuals estimate their personal carbon footprint based on their lifestyle choices. The carbon footprint can also be calculated for whole countries or specific sectors. By understanding the carbon footprint of different activities, products, companies, or countries, we can make comparisons and identify areas where emissions can be reduced.

The carbon footprint is commonly expressed as carbon dioxide equivalent (CO2eq) per unit of comparison. This means that it takes into account not only carbon dioxide emissions but also other greenhouse gases like methane and nitrous oxide. The greenhouse gas protocol, a set of standards for tracking greenhouse gas emissions, includes all the important greenhouse gases in its calculations.

The carbon footprint is divided into three scopes: Scope 1, Scope 2, and Scope 3. Scope 1 emissions are the direct emissions from an organization or activity, like burning fossil fuels. Scope 2 emissions are the indirect emissions from the purchase of electricity, heat, or steam. Scope 3 emissions are the indirect emissions from sources outside the organization's control, such as transportation or waste disposal.

Calculating the carbon footprint requires expert knowledge and careful examination of what should be included. There are software tools available to assist in the calculation process, and input-output analysis is often used to analyze global supply chains. It is important to note that the carbon footprint is just one indicator of environmental impact and should be considered alongside other factors like water usage, biodiversity loss, and habitat destruction.

The carbon footprint concept has been criticized for shifting responsibility from corporations to individuals and for not taking into account other environmental impacts. However, it remains a useful tool for comparing the climate-relevant impacts of different entities and for identifying areas where emissions can be reduced.