Japan drastically scaled back its target for reducing greenhouse gas emissions.

The country wants to reduce emissions by 3.8 per cent from their 2005 level by 2020.

Government spokesman Yoshihide Suga claimed that the revision was necessary because the earlier goal of a 25 per cent reduction from the 1990 level was unrealistic.

The new target represents a 3 per cent increase on 1990 emissions.

Given Japan's status as the world's third-largest economy and fifth-largest source of greenhouse gas emissions, the decision could be a significant setback for climate talks underway in Warsaw.

Under the 1997 Kyoto Protocol Japan had pledged to cut greenhouse gas emissions by 6 per cent to 1.186 billion tons a year over the five years to March 2013.

It has since opted out of the agreement, though it came close to meeting its goal before the 2011 accident at the Fukushima Dai-Ichi nuclear power plant.

The resulting shift back toward reliance on coal, oil and gas for power generation hindered further progress.

Emissions in the year that ended in March were up 2.8 per cent from the year before and at 1.207 billion tons, the second highest after a record 1.218 in 2007.

Mr Suga claimed that the 25 per cent reduction goal had been "completely baseless."

The initial reaction to Japan's announcement in Warsaw was consternation.

"I don't have any words to describe my dismay," said Chinese delegation deputy head Su Wei.