The Kyoto global warming pact requires nations to cut emissions below 1990 levels, but critics say that is too difficult because emissions in many countries have risen dramatically since then.
Instead, Japan will push to set the base year for 2005 in an agreement that is meant to take effect when Kyoto expires in 2012, said Takao Kitabata, vice-minister of Japan's Ministry of Economy, Trade and Industry.
Kitabata argued 1990 levels are too easy to meet for industrial nations of the European Union, which has absorbed Eastern European countries whose emissions dropped in the 1990s. The EU backs continuing with 1990 as the base year.
"Comparisons with 1990 levels are extremely unfair, and that is the Japanese government's stance," Kitabata told reporters. "It would be fair to set 2005 as the base year."
Kitabata, the top bureaucrat at the ministry, also argued that Japan accepted unfairly tough conditions in the Kyoto accord in 1997. He called for a more equitable burden-sharing in the next pact.
"What happened in Kyoto was that we were forced to swallow disadvantageous conditions for diplomatic reasons," he said.
Kitabata also said that having 1990 as the base year "would be also difficult to obtain support from China, India and other emerging nations because that would be an enormous burden for them."
The Kyoto Protocol requires 36 industrialized countries to cut emissions of greenhouse gases such as carbon dioxide an average of 5 percent below 1990 levels between 2008 and 2012.
The United States is the only major industrialized nation to have remained outside Kyoto, arguing that such cuts would hurt its economy. Washington also says the pact is unfair because it doesn't oblige major emitters such as China to make reductions.
Japan is struggling to meet its Kyoto obligation of 6 percent cuts. While Tokyo has called for cutting global emissions by 50 percent by 2050, it has not yet set a firm base year for such cuts.
Nations have agreed at U.N.-led talks to put together a new climate change agreement by 2009 to take effect when Kyoto ends in 2012.
The United States and Japan are calling on China and other emerging emitters to assume a greater burden for reducing greenhouse gases blamed for global warming, but developing countries say wealthy countries should take more responsibility because they industrialized first.