UN Secretary General Antonio Guterres warned global leaders Friday that upcoming climate talks in the Scottish city Glasgow could fail without renewed trust among G20 leaders, calling for "more ambition and more action".

"There is a serious risk that Glasgow will not deliver," Guterres told journalists, on the eve of a weekend meeting of G20 heads of state in Rome.

The leaders of advanced economies are expected to discuss climate change ahead of marathon UN COP26 climate talks beginning Monday in Glasgow, but those talks could fail if trust between G20 members was not re-established, Guterres said. 

"If we want real success and not just a mirage, we need more ambition and more action," Guterres said. 

"That will only be possible with a massive mobilisation of political will, and that requires trust among the key actors," Guterres said, adding that such trust was "in short supply".

Guterres has repeatedly sounded the alarm before, and warned again Friday of the coming "climate catastrophe" if G20 countries fail to act, pointing to their responsibility as producers of the largest share of global emissions.

"This is not a prediction, this is a warning," he said.

"We are still on time to put things on track, and I think the G20 meeting is the opportunity to do that."

"On all our climate goals we have miles to go and we must pick up the pace," said Guterres. 

"It is not too late but we must act now." 

Continued disagreements between G20 member countries, which are at different stages of development, come amid the absence of two key players -- Russian President Vladimir Putin and China's Xi Jinping -- who will attend only by video link.