MADRID — After two weeks of contentious negotiations, world leaders put in charge of averting a cluster of accelerating climate threats remained at loggerheads late Saturday about whether they could commit, just on paper, to raise voluntary climate targets next year.

The annual talks, formally known as the Conference of Parties, which had been scheduled to end on Friday, were meant to hammer out the final details of the landmark 2015 Paris climate accord, and expectations initially ran high that they would yield a collective political call for raising climate targets.

That is vital for the future of millions. With greenhouse gas emissions on their current trajectory, average global temperatures are on pace to increase to levels where heat waves are very likely to intensify, storms are set to become more severe, and coastal cities are at risk of drowning, according to scientific consensus.