KATOWICE, Poland - The United Nations secretary-general called on countries to make compromises and sacrifices in talks over tackling global warming, as some observers warned the meeting in Poland could collapse without an agreement on key issues.

Making his second dramatic appeal in the space of 10 days, Antonio Guterres told ministers and senior diplomats from almost 200 countries that they should consider the fate of future generations.

“This is the time for political compromises to be reached,” he said. “This means sacrifices, but it will benefit us all collectively.”

His call came as the two-week meeting in Katowice shifted from the technical to political phase, with ministers taking over negotiations.

Campaign groups warned of the risks of failure and accused powerful players such as the European Union of not pushing hard enough to reach an agreement.

“A new leadership must step up,” said Vanessa Perez-Cirera of the environmental group WWF. “We cannot afford to lose one of the twelve years we have remaining.”

She was referring to a recent scientific report by a U.N.-backed panel that suggested average global warming can only be halted at 1.5 degrees Celsius (2.7 Fahrenheit) if urgent action is taken by 2030, including a dramatic reduction in use of fossil fuels.

Endorsing the report by the Intergovernmental Panel on Climate Change became a crunch issue over the weekend, with the United States, Russia, Saudi Arabia and Kuwait opposing the move.

Jean-Pascal Ypersele, a former deputy chair of the panel, said whether or not countries believe the conclusions of the report was irrelevant because the science was clear.

“Nobody, even the so-called superpowers, can negotiate with the laws of physics,” he said.

Ypersele called for the 1.5-degree target - already mentioned in the 2015 Paris accord - to be recognized in the final text.

“It's a question of survival for a large part of humanity, and many other species,” he said.

Poland, which is chairing the talks, was circulated a condensed draft text Wednesday running to about 100 pages, down from about 300 at the start of the talks.

The Dec. 2-14 meeting is supposed to finalize the rules that signatories of the Paris accord need to follow when it comes to reporting their greenhouse gas emissions and efforts to reduce them.

Jennifer Morgan, the head of environmental group Greenpeace, said the current drafts contain too many loopholes to be effective, including how countries calculate the amount of emissions absorbed by trees when submitting their reports.

“One proposal is that every country can pick to count it however they want to,” Morgan said. “There's no scientific integrity in that.”

Poor countries, meanwhile, want assurances on financial support to tackle climate change. Many say they are already seeing the effects of global warming in droughts, floods and other disasters made worse by emissions that were generated mostly by developed nations.

A third objective of the talks is getting governments to make a firm commit to raising ambitions in the coming two years, albeit without any precise figures.

Guterres, who made a detour on his way to Yemen peace talks in Sweden, said failure to reach agreement in Katowice “would compromise our last best chance to stop runaway climate change.”

“It would not only be immoral, it would be suicidal,” he added.

Guterres said that while he and most people in the room wouldn't be alive by the end of the century, children alive today would be.

“I do not want my granddaughters or anybody else's to suffer the consequences of our failures,” he said, “They would not forgive us if uncontrolled and spiraling climate change would be our legacy to them.”