In an emphatic address to the 194-nation talks, the UN chief highlighted studies by scientists who say the world has a limited gateway to cut carbon emissions or risk irreversible damage to the planet.

"I'm deeply concerned that our efforts so far have been insufficient, that despite the evidence and many years of negotiation we are still not rising to the challenge," Ban said as the two-week talks entered the final four days.

"Business as usual cannot be tolerated," he said. "Cancun must represent a breakthrough…" "The world, particularly the poor and vulnerable, cannot afford the luxury of waiting for the perfect agreement," Ban said, adding: "Every country can and must do more."

Host Mexico has encouraged nations to look for building blocks to an eventual climate accord, hoping to undo some of the damage from last year's Copenhagen summit.

China has climbed down from its past refusal on verification of nations' promises to fight climate change after India drafted a compromise under which all countries responsible for more than one percent of emissions would submit to verification but not face ‘punitive consequence’.

AFP