A carbon footprint is "the total set of GHG (greenhouse gas) emissions caused directly and indirectly by an individual, organization, event or product" (UK Carbon Trust 2008). An individual, nation, or organization's carbon footprint is measured by undertaking a GHG emissions assessment. Once the size of a carbon footprint is known, a strategy can be devised to reduce it.
Carbon offsets, or the mitigation of carbon emissions through the development of alternative projects such as solar or wind energy or reforestation, represent one way of managing a carbon footprint.
Kyoto Protocol, carbon offsetting, and certificates
Carbon dioxide emits to air (and the emissions of other GHG's) are almost exclusively associated with the conversion of energy carriers like natural gas, crude oil, etc.
The Kyoto Protocol defines legally binding targets and timetables for cutting the greenhouse-gas emissions of industrialized countries that ratified the Kyoto Protocol. Accordingly, from an economic or market perspective, one has to distinguish between a mandatory market and a voluntary market. Typical for both markets is the trade with emission certificates: