On Feb. 16, the Kyoto Protocol, aimed at curbing the air pollution blamed for global warming, took effect. To become valid, the accord had to be ratified by at least 55 countries, including developed countries that accounted for at least 55 percent of carbon dioxide (CO2) and other greenhouse gas emissions from "Annex I" countries.
The final requirement was met in November when Russia ratified the agreement. The protocol came into force 90 days later.
The accord requires Japan to cut its greenhouse-gas emissions between 2008 and 2012 by 6 percent from 1990 levels. Japan could try to reduce CO2 emissions -- which accounts for 90 percent of all greenhouse gases -- through voluntary programs, restrictions, economic measures or a combination thereof.