In a grim and powerful assessment of the future of the planet, the leading international network of climate scientists has concluded for the first time that global warming is “unequivocal” and that human activity is the main driver, “very likely” causing most of the rise in temperatures since 1950.

They said the world was in for centuries of climbing temperatures, rising seas and shifting weather patterns — unavoidable results of the buildup of heat-trapping gases in the atmosphere.

But their report, released here on Friday by the Intergovernmental Panel on Climate Change, said warming and its harmful consequences could be substantially blunted by prompt action.

While the report provided scant new evidence of a climate apocalypse now, and while it expressly avoided recommending courses of action, officials from the United Nations agencies that created the panel in 1988 said it spoke of the urgent need to limit looming and momentous risks.

“In our daily lives we all respond urgently to dangers that are much less likely than climate change to affect the future of our children,” said Achim Steiner, executive director of the United Nations Environment Program, which administers the panel along with the World Meteorological Organization. “Feb. 2 will be remembered as the date when uncertainty was removed as to whether humans had anything to do with climate change on this planet,” he went on. “The evidence is on the table.”