"Soon will come a day when climate change escapes all control. We are on the verge of the irreversible," Chirac told the meeting, which began just hours after the release of a key United Nations scientific report on global warming.

"Faced with this emergency, the time is not for half measures. The time is for a revolution -- a revolution of our awareness, a revolution of the economy. A revolution of political action."

Chirac opened the two-day gathering flanked by European Commission President Jose Manuel Barroso, Orthodox Patriarch Bartholomew I and the head of the UN General Assembly, Sheikha Haya Rashed Al-Khalifa.

The Paris conference aims to build support for the creation of a United Nations environment agency, with more far-reaching powers and greater means than the existing United Nations Environment Programme.

"Our international political organisation is inadequate for dealing with the vital challenge of the 21st century -- the question of the environment," Chirac told the gathering of 200 delegates, including environment ministers and scientists from more than 50 countries.

High-profile delegates at the meeting were to include the Kenyan environmentalist and Nobel Peace Prize winner Wangari Maathai and the British economist and climate expert Nicolas Stern.

The Intergovernmental Panel on Climate Change (IPCC), the UN's paramount scientific authority on global warming, said on Friday global warming was almost certainly caused by humans and will be unstoppable for centuries to come.

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