That wipes out a significant chunk of reductions Japan achieved during 2008-2010 through energy efficiency, credits for helping developing countries devise cleaner technologies and planting trees to absorb carbon dioxide. Officials believe Japan can still barely meet its commitment under the Kyoto Protocol to reduce emissions during the five-year period through 2012 by an average of 6 percent from 1990 levels.
Some experts see a model in Germany, which turned decisively against nuclear power after the Fukushima crisis, shutting down eight reactors and planning to close the remaining nine nuclear power plants by 2022. Yet its greenhouse gas emissions decreased 2 percent last year from 2010, and by 26.5 percent compared to 1990.
While a mild winter seems to have helped, Germany's growing renewable energy sector, which now accounts for over 20 percent of power generation, played a key role in that emissions decline, experts say. The German government has been actively promoting green energy for more than a decade, and aims to boost the share of renewables to 35 percent by 2020 — and 80 percent by 2050.
"If the government puts in place the right set of policies and incentives, then Germany is an example that you can reduce nuclear and greenhouse gases at the same time," said Jennifer Morgan, director of climate and energy program at the World Resources Institute in Washington.
Germany, however, has a safety net that Japan lacks. If it has shortfalls or blackouts, Germany can buy electricity from neighboring countries through the European power grid. The island nation of Japan has no such fallback.
Japanese politics, with its high leadership turnover, internal power battles and gridlock, is another obstacle. Its track record in recent years has been marked with indecision.
If Japan can put its collective mind to expand renewable energy, it too can achieve similar levels as Germany, said Sei Kato, deputy director at Environment Ministry's Low Carbon Society Promotion Office.
"We have the technological know-how. Japan can do anything Germany can," Kato said.
Associated Press Writer Juergen Baetz in Berlin contributed to this report.