Key points about Kyoto Protocol:
Obliges industrialized countries, as group, to cut emissions of carbon dioxide and other greenhouse gases by 5.2 percent from 1990 level by 2012. Gases believed to trap heat in atmosphere, warming Earth.
Nations may offset emission requirements by properly managing forests and farmlands that absorb carbon dioxide. Can earn further credits by helping developing countries cut emissions.
Allows for "emissions trading" — buying and selling of right to pollute, to give profit motive for businesses to reduce emissions.
Member countries face mandatory punishment if they fail to meet emission targets.
Treaty must be ratified by 55 countries responsible for 55 percent of global greenhouse gas emissions. Takes effect 90 days after receiving sufficient ratification.
United States rejected pact in 2001, saying it would harm its economy and unfairly favored developing countries.