Although the ruling Democratic Party of Japan vowed to slash 25 percent of greenhouse gas emissions by 2020 from 1990 levels, the U.S., India, China and other global players must also join a worldwide framework for Japan to implement the pledge, according to Economy, Trade and Industry Minister Masayuki Naoshima.

"Efforts to fight global warming should be worldwide, and it won't be solved by efforts of just Japan and Europe," he said during a joint interview with The Japan Times on Thursday.

Critics say the DPJ's target is too bold to achieve and would prove too much of a burden to companies and households.