A global warming target could be missed three times over if countries fail to promote clean energy, the International Energy Agency warned Thursday, amid a possible slowdown in atomic power growth.

An inside view of a nuclear reactor of the nuclear power station in Gundremmingen, southern Germany, during regular maintenance work in 2010.

Nuclear fuel does not emit carbon dioxide, making it a serious option for "clean energy" proponents over fossil fuels, but governments around the world have turned more cautious on it in the wake of the Fukushima crisis in Japan.

The IEA\'s deputy head Richard Jones however cautioned that global warming could accelerate much faster and lead to catastrophic consequences if the international community fails to adopt a more aggressive clean energy policy.

"We are not on the pathway to limit global temperatures," he told the Foreign Correspondents Club in Hong Kong, referring to an international goal to restrict warming to two degrees Celsius by the end of the century.

The target was set by countries at the Cancun meeting in December 2010.

"If you miss it by 0.1 degree Celsius nobody cares but the problem is it looks like we are on track for more than six degrees Celsius (rise)," he said.

"That is serious. We really don\'t know what will happen," said the deputy head of the Paris-based agency, set up to monitor energy use.

In its annual report last year, the IEA projected that 360 gigawatts of nuclear generating capacity would be added worldwide by 2035, on top of the 390 gigawatts already in use.

However fears over the use of nuclear power could see the IEA halve its projection to 180 gigawatts, its chief economist Fatih Birol told AFP earlier this month.

Jones said the earlier projection would be "overly optimistic in today\'s environment", and that the IEA will re-evaluate the statistic, but declined to give any figures.

Germany has announced the temporary shutdown of its seven oldest nuclear reactors while it conducts a safety probe in light of Japan\'s atomic emergency, triggered by an earthquake and tsunami that crippled the power station.

Switzerland suspended plans to replace its ageing atomic plants, while in France -- where nuclear makes up 75 percent of electricity production -- environmental groups have called for a referendum on the future use of atomic power.