– Global talks to combat climate change risked breaking up with little to show for them, participants here said Wednesday, with the hostile U.S. stance on aggressive action leaving a leadership void that other countries have been reluctant or unable to fill.

The year's largest gathering of climate negotiators, with nearly 200 countries represented, is seen as a crucial moment when the world will either commit to ramping up its ambitions to attack the issue or risk falling even further behind in staving off the worst effects of global warming.

Yet with two days to go before the talks are scheduled to close, participants say they have seen scant progress. U.N. Secretary-General Antonio Guterres said Wednesday that "key political issues remain unresolved" and warned bluntly that "we are running out of time."

"I understand that none of this is easy. I understand some of you will need to make some tough political decisions," Guterres told the delegates in this snowy, sun-starved Polish city. "To waste this opportunity would compromise our last best chance to stop runaway climate change. It would not only be immoral, it would be suicidal."

Gridlock has been a common trait of past U.N. climate talks, especially in the waning days as top-level diplomats often work well into the night to hammer out the most difficult and fraught details of policy. And getting 197 countries to find consensus on anything is a perpetually difficult task.

But despite the high stakes, there appeared to be little optimism for much of Wednesday, with negotiators refusing to make the sort of aggressive commitments to action that scientists say are needed. Many participants and observers said the absence of a high-powered U.S. role helped explain why.

The United States, which had been a heavyweight player at U.N. climate conferences under previous administrations, has sent a low-profile delegation to this year's summit under President Donald Trump. The administration has said it plans to exit the landmark Paris climate agreement, under which the world agreed to cut emissions, and while U.S. negotiators remain engaged behind the scenes, they are not taking a top role.

On Wednesday evening, as other countries were publicly pushing for more aggressive action, U.S. officials were not among them.

"The United States supports a balanced approach that promotes economic growth, improves energy security and protects the environment," Judith Garber, a veteran State Department diplomat, said in an address to the gathering.