The Japanese government on Wednesday submitted ratification documents to the United Nations for the 1997 Kyoto Protocol on global warming, government officials said.

The Kyoto Protocol requires industrialized countries to cut their greenhouse-gas emissions from 1990 levels by an average of 5.2 percent between 2008 and 2012.

The pact will enter into force 90 days after it is ratified by 55 states who represent 55 percent of the carbon dioxide emitted by industrialized countries in 1990.

Thursday is the deadline for procedures to be taken for the pact to be ratified in time for its enforcement during the World Summit on Sustainable Development, which is scheduled to take place in Johannesburg from Aug. 26 to Sept. 4.

Ratification by Russia and East European countries is essential because the United States — the world's largest emitter of carbon dioxide — has withdrawn from the pact. Russia represents about 17 percent of total carbon dioxide emissions in the world, but it is unclear when it will ratify the pact.

With Japan's move, the number of ratifying countries stands at 74, which represents nearly 40 percent of total carbon dioxide emissions.