In what was widely denounced as one of the worst outcomes in a quarter-century of climate negotiations, United Nations talks ended early Sunday morning with the United States and other big polluters blocking even a nonbinding measure that would have encouraged countries to adopt more ambitious targets for reducing greenhouse gas emissions next year.

Because the United States is withdrawing from the Paris climate agreement, it was the last chance, at least for some time, for American delegates to sit at the negotiating table at the annual talks — and perhaps a turning point in global climate negotiations, given the influence that Washington has long wielded, for better or worse, in the discussions.

The Trump administration used the meeting to push back on a range of proposals, including a mechanism to compensate developing countries for losses that were the result of more intense storms, droughts, rising seas and other effects of global warming.

The annual negotiations, held in Madrid this year, demonstrated the vast gaps between what scientists say the world needs and what the world’s most powerful leaders are prepared to even discuss, let alone do.