Tokyo ? Japan hopes to slash greenhouse gas emissions and fight global warming with a revolutionary plan to pump carbon dioxide into underground storage reservoirs instead of releasing it into the atmosphere, an official said Monday.

The proposal aims to bury 200 million tons of carbon dioxide a year by 2020, cutting the country’s emissions by one-sixth, said Masahiro Nishio, an official at the Ministry of Economy, Trade and Industry. Introduced last month, the plan is still under study.

Underground storage of carbon dioxide underlines the new urgency felt by industrialized countries trying to rein in the effects of global warming. But capturing carbon dioxide from factory emissions and pressurizing it into liquid form, scientists can inject it into underground aquifers, gas fields or gaps between rock strata, safely keeping it out of the air.

Japan has no commercial underground carbon dioxide storage operations, Nishio said. But the proposed project would dwarf similar operations under way in Norway, Canada and Algeria, each of which pump about 1 million tons a year.

Tackling carbon dioxide is a top priority for Japan, the world’s second-largest economy. The country expels 1.3 billion tons of carbon dioxide a year, making it one of the world’s top offenders, despite being a key driver behind to the Kyoto Protocol – an international agreement to cut global output of carbon dioxide by 2012.

Underground storage could begin as early as 2010, but there are still many hurdles to overcome, Masahiro said.