Guterres told delegates from over 130 countries meeting in the Polish city of Katowice that they had less than three days to find the political will to reach difficult compromises, sacrifices and common ground needed for a deal.

"Failing here in Katowice would send a disastrous message to those who stand ready to shift to a green economy," he said. "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."

Three years to the day after the Paris climate accord was adopted by over 190 countries, delegates in the Polish coal-mining city are still grappling with how the accord will be implemented.

This slow progress after more than a week of negotiations prompted Michal Kurtyka, the Polish president of the talks, to tell delegates time was precious and they needed to find wordings which were acceptable to all.

Environmental activists and some developing countries have also raised concern that the rulebook could fall short of pushing countries towards curbing their emissions to meet the Paris targets.

"The clock is ticking. While we spend time debating texts and demanding their implementation, the planet outside is deteriorating. Species are becoming extinct. Habitats disappearing. Emissions piling up," Brazilian Environment Minister Edson Duarte said.

Guterres said a recent report by the U.N. Intergovernmental Panel on Climate Change acknowledged what global warming beyond 1.5 degrees will mean for billions of people, especially those who live in small island states.

The report outlined a catastrophic future if no action was taken by countries immediately, he said, adding that the window of opportunity was closing.

The Paris Agreement aims to restrict warming to "well below" two degrees Celsius (3.6 Fahrenheit) above pre-industrial times.

"This may sound like a dramatic appeal, but it is exactly this: a dramatic appeal," Guterres said.

REUTERS