Changes that are directly or indirectly attributed to human activity and alter the composition of the world’s atmosphere and that is added to that caused by the natural climatic variability observed over comparable periods.
Entry into force
Intergovernmental agreements, including protocols and amendments, are not legally valid until ratified by a certain number of countries. For the UNFCCC creation, it took 50 countries; as for ratifying the Kyoto Protocol, at least 55 countries were required...