By Daniel Wallis NAIROBI, Jan 30 (Reuters) - A climate change summit of world leaders would help drive momentum spurred by damning new reports and changing attitudes in Washington to global warming, a U.N. environment spokesman said on Tuesday. The summit, tentatively planned for September, would focus on the hunt for a successor to the Kyoto Protocol on cutting greenhouse gases linked to dire forecasts of heat waves, floods, droughts and rising sea levels. This week, the broadest scientific study so far of the human effect on climate change will conclude there is at least a 90 percent chance human activities, mainly burning fossil fuels, are to blame for most of the warming in the last 50 years. Putting climate change high on his list of priorities after taking over at the helm of the United Nations, Secretary-General Ban Ki-moon was holding talks with U.N. Environment Programme (UNEP) officials at their headquarters in Kenya. "High on the agenda will be a special climate change summit," said Nick Nuttal, spokesman for UNEP boss Achim Steiner. "This is a critical year and we must bring developed and developing countries together towards a conclusion." Under Kyoto, 35 industrial nations agreed to cut carbon dioxide emissions by 5 percent below 1990 levels by 2008-12. "HAVE TO MOVE NOW" The United States pulled out in 2001, arguing that Kyoto would cost jobs and wrongly excluded developing nations from goals for 2012. Still, U.S. President George W. Bush said last week climate change was a "serious challenge". The seriousness of that challenge will be underlined in Friday's release of a study by 2,500 scientists from more than 130 countries for the Intergovernmental Panel on Climate Change (IPCC). Scientific sources say the report, the fourth of its kind, will foresee global average temperatures rising to 2.0 to 4.5 degrees Celsius (3.6 to 8.1 Fahrenheit) above pre-industrial levels by 2100, with a "best estimate" of a 3.0 C (5.4 F) rise. It will say there is at least a 90 percent chance humans are to blame for most of the warming over the last five decades. The previous report, in 2001, put the probability at 66 percent. "It is now absolutely clear that we have to move together and we have to move now," Nuttal said.
