CO2 certificates are used to compensate for CO2 emissions of any kind. In the regulated market, companies have to buy one CO2 certificate per ton of CO2 they produce. In the voluntary market, however, private people are also able to buy CO2 certificates to compensate for their private CO2 emissions.
One CO2 certificate corresponds to the saving of one ton of CO2 – physically bound through a climate protection project that has demonstrably saved or reduced this amount of CO2. The Kyoto Agreement has made this possible – through the purchase and retirement of such a certificate, you can offset one ton of CO2 that is emitted at any place on the planet.