A summit last year of the Group of Eight rich nations agreed to "seriously consider" halving global emissions by 2050 in hopes of halting global warming.

To achieve such a goal, Japan -- which is already far behind in meeting its current commitments -- would need to cut emissions by 85 percent by 2050 from 1990 levels, said Norichika Kanie, assistant professor at the Tokyo Institute of Technology.

His joint research with Yasuaki Hijioka, researcher at the National Institute of Environmental Studies, found that the United States would need to cut emissions by 88 percent and the European Union by 83 percent.

He made the calculations on the premise that all countries will emit at the same level on a per capita basis by 2050.

The United States has rejected the Kyoto Protocol, the landmark treaty requiring emissions cuts through 2012, arguing that it is unfair by making no demands on fast-growing polluters in the developing world.

The Japanese study found that China would need to cut emissions by 35 percent while India, whose current per capita emissions are small, could actually increase its output by 137 percent by 2050.

But even if all countries achieve the daunting tasks, the average global air temperature will rise by 2.2 to 2.6 degrees Celsius by 2050, Kanie said.

"It may seem impossible to achieve such shocking and ambitious targets, but I think it is a matter of changing lifestyle and not necessarily in an austere way," Kanie said.

"For example, I often ride my bike instead of driving a car. If the government provided a more bicycle-friendly infrastructure, people's lifestyles will change for a low-carbon society," he said.

The Kyoto Protocol, signed in 1997 in the ancient Japanese city, requires rich nations to slash emissions by an average of five percent by 2012 from 1990 levels, with a different figure set for each country.

A UN conference in Bali in December agreed to seal a new pact by the end of 2009 to spell out future commitments.

The European Union has unilaterally set a goal of slashing emissions by 20 to 30 percent by 2020 from 1990 levels and has offered to go further if other major economies join the effort.

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