The key facts on global warming are already known and leaders should not wait for the next edition of the UN climate panel's report to step up action, the body's top scientist says.
The 4th Intergovernmental Panel on Climate Change (IPCC) report, released in 2007, "is very clear," Rajendra Pachauri told AFP in Paris, before a five-day meeting of the body in Brest, France.
The fifth multi-volume assessment, which summarises peer-reviewed science to help policy makers make decisions, is due out in 2013/14.
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"We have enough evidence, enough scientific findings which should convince people that action has to be taken," he said after a round-table discussion with French Environment Minister Nathalie Kosciusko-Morizet.
"Based on observation, we know that there will be more floods, more drought, more heat waves and more extreme precipitation events. These things are happening," Pachauri said.
Pachauri, whose organisation shared the Nobel Peace prize in 2007 with former US vice-president Al Gore, announced that a special IPCC report on the relation of extreme weather events and disasters to climate change, and how to adapt to them, would be released on November 19.
The much anticipated report will review efforts by scientists to connect the dots between well identified long-term climate change trends and short-term weather patterns.
While scientists agree that the risk of more violent storms and flooding will rise over time, it remains difficult to attribute any single weather event to climate change, they say.
Pachauri cautioned that the widely accepted goal of preventing average global temperatures from increasing by more than 2 degrees Celsius compared with preindustrial times is fast slipping beyond reach.
To achieve that goal in a cost-effective manner "concentration of greenhouse gases [in the atmosphere] must peak not later than 2015", he said.
The IPCC weathered a firestorm of controversy in late 2009 and 2010 when several minor but embarrassing errors were uncovered in the massive 2007 report, leading to initiatives to tighten standards for inclusion and review of material.
Pachauri was re-elected chairman of the IPCC in 2008.