Scientists say they are more certain than ever that humans are the main cause of global warming.

The Intergovernmental Panel on Climate Change said Friday it is "extremely likely" that global warming was man-made. In its last report in 2007, the United Nations panel had said it was "very" likely.

U.S. Secretary of State John Kerry called the latest report another "wake-up call." In a statement Friday, he said "those who deny the science or choose excuses over action are playing with fire."

The co-chair of the IPCC working group that wrote the new report said it finds that the atmosphere and oceans have warmed, snow and ice have diminished, the global mean sea level has risen and the concentrations of greenhouse gases have increased.

The U.N. panel predicts global temperatures and sea levels will continue to rise this century . It says the Earth will likely see more heatwaves, droughts and floods. And it warns some effects of global warming will last far beyond the lifetimes of current generations.

The assessments of the IPCC are important because they form the scientific basis of U.N . negotiations on a new climate deal. In a video statement, U.N. Secretary-General Ban Ki-Moon said the report will be "essential" for governments working to finalize an agreement in 2015. But it is unclear whether they will commit to the greenhouse-gas emissions cuts that scientists say will be necessary to limit damage to the climate.

The findings released Friday are part of a 2,000-page report. The IPCC will put out two more reports next year.