PARIS - The UN's top climate scientist on Thursday urged a key conference on global warming to set tough mid-term goals and warned carbon emissions had to peak by 2015 to meet a widely-shared vision.
Rajendra Pachauri, chairman of the Nobel-winning Intergovernmental Panel on Climate Change (IPCC), said the talks in Copenhagen in December must focus on 2020, a far more important target than mid-century.
"Strong, urgent and effective action" is needed, Pachauri told a meeting of ministers of the International Energy Agency (IEA) in Paris.
"It is not enough to set any aspirational goal for 2050, it is critically important that we bring about a commitment to reduce emissions effectively by 2020," he said.
Pachauri added that over the last two years he had witnessed "a massive explosion of awareness and therefore willingness to take action" in climate change.
But, he said, the deal in Copenhagen had to be consistent with the findings of scientists, who say greenhouse gases that trap heat from the Sun are already affecting the climate system, and grave potential problems lie ahead.
The Group of Eight (G8) and other countries have endorsed the target of pegging warming to no more than two degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial times.
Pachauri said this target "is not without some fairly serious impact."
"If this path of mitigation is to be embarked on, to ensure stabilisation of temperatures at the level that I mentioned (2 C, 3.6 F), then global emissions must peak by 2015," he said.
The December 7-18 Copenhagen talks are taking place under the 192-nation UN Framework Convention on Climate Change (UNFCCC).
The objective is a treaty that will tackle carbon emissions and their impacts, and encourage a switch to cleaner energy after 2012, when the current Kyoto Protocol pledges expire.
But UN talks have been bogged down by what is largely a divide between rich and poor countries, complicated by the US position.
President Barack Obama is sweeping away many of George W. Bush's legacy climate policies but has been unable to satisfy demands for deep, swift cuts in US carbon emissions.
He also faces a race against the clock to steer cap-and-trade legislation through Congress before the Copenhagen conference opens.
Pachauri told a press conference that it might take until next year for Washington to formulate its commitments on 2020.
"A reasonably good agreement" could emerge in Copenhagen, Pachauri said, adding though that he would not be dismayed by a delay if this provided a better outcome.
"If we are not getting a good agreement, then the global community really has the option of meeting again six months later or three months later or whatever," he said.
"I think we really have to keep at it until we can hammer out an agreement that meets the requirements of what science has clearly placed before us. It means a delay, it means some degree of disappointment all around, but who knows in the end you might get a much better agreement six months later."