Ban told an international U.N. school conference on global warming, meeting in the U.N. General Assembly hall, that the world needed a more coherent system of international environmental governance and he hoped the US would take the lead in the climate-change fight beyond Kyoto's end in 2012.

"The majority of the United Nations work still focuses on preventing and ending conflict," Ban said. "But the danger posed by war to all of humanity and to our planet is at least matched by the climate crisis and global warming.

"In coming decades, changes in our environment and the resulting upheavals from droughts to inundated coastal areas to loss of arable land are likely to become a major driver of war and conflict."

Last month a U.N.-organized panel of 2,500 top climate scientists from more than 130 nations blamed human activities for global warming and predicted more droughts, heat waves and a slow rise in sea levels that could continue for more than 1,000 years even if greenhouse-gas emissions were capped.

The panel predicts a "best estimate" that temperatures would rise by between 1.8 and 4.0 degrees Celsius (3.2 and 7.8 Fahrenheit) in the 21st century.