With Japan's oil and gas plants firing at full capacity, officials here say there is little chance of meeting a pledge to cut greenhouse gas emissions significantly over the next decade, a startling retreat for a country that once spearheaded an international agreement on climate change.

The earlier, ambitious target to slash emissions 25 percent from 1990 levels by 2020 has been overrun by a more urgent, short-term need: to burn fossil fuels and maintain a steady electricity supply in the wake of the country's abrupt turn away from nuclear power.

Japan, still the world's third-largest economy, was once the poster child for aggressive environmental policy. It chaired the historic conference 15 years ago that led to the Kyoto Protocol, the world's first climate pact, and it pioneered clean technology, using decades of research to boost energy efficiency.

The centerpiece of Japan's efforts to combat global warming was nuclear power. But since last year's Fukushima nuclear complex disaster, this resource-poor country has been forced to sharply increase its use of dirtier fossil fuels.