It’s a measure of the total amount of harmful greenhouse-gas emissions that people produce, either directly or indirectly. These gases warm the atmosphere by absorbing heat that’s radiated by the earth, then releasing only a portion of that heat into space. The most dangerous, long-lasting greenhouse gases produced by humans are carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons (aerosols containing this were banned in the U.S. nearly 30 years ago). Carbon dioxide, or CO2, is the most pervasive of the evil gases (a molecule stays airborne for more than a century), and since it’s tough to separate and quantify each distinct greenhouse gas, scientists commonly use CO2 to measure the global-warming problem.
A carbon footprint is made up of the sum of two parts, the primary footprint (shown by the green slices of the pie chart) and the secondary footprint (shown as the yellow slices).
1. The primary footprint is a measure of our direct emissions of CO2 from the burning of fossil fuels including domestic energy consumption and transportation (e.g. car and plane). We have direct control of these.
2. The secondary footprint is a measure of the indirect CO2 emissions from the whole lifecycle of products we use - those associated with their manufacture and eventual breakdown. To put it very simply – the more we buy the more emissions will be caused on our behalf.
