United Nations leaders will demand "concrete results" from the looming Cancun climate summit as global warming is accelerating, a top UN organizer of the event said Monday.

A scientist stands in front of a globe during the United Nations Climate Change Conference in Copenhagen in 2009.

Robert Orr, UN under secretary general for planning, said the next Intergovernmental Panel on Climate Change report on global warming will be much worse than the last one.

Representatives from 194 countries are to meet in the Mexican resort city of Cancun from November 29 to December 10 for a new attempt to strike a deal to curb greenhouse gases after 2012.

Orr told reporters that negotiators heading for the Cancun conference "need to remind themselves, the longer we delay, the more we will pay both in terms of lives and in terms of money."

He said UN Secretary General Ban Ki-moon would make it clear to world leaders in Cancun "that we should not take any comfort in the climate deniers\' siren call."

"The evidence shows us quite the opposite-- that we can\'t rest easy at all" as scientists agree that climate change "is happening in an accelerated way."

"As preparations are underway for the next IPCC report, just about everything that you will see in the next report will be more dramatic than the last report, because that is where all the data is pointing."

The fourth IPCC assessment released in 2007 said that global warming is "unequivocal" and mainly caused by human activity.

Its next report, involving contributions from thousands of scientists around the world, is due in 2014.

With many countries fearful of a repeat of last year\'s bitter Copenhagen summit failure, Orr said that progress is possible in Cancun.

If governments "understand the peril that their populations are in, it is much easier to get over the political hurdles to do what you have to do," he said.

The United Nations wants breakthroughs on verifying deforestation and financing to combat the lost of tropical forests.

Efforts to speed up technology transfers to combat global warming and financing projects to slow the phenomenon could also be advanced, Orr said.

Thirty billion dollars of emergency funding over three years was agreed at Copenhagen and a UN panel on how to raise 100 billion dollars a year from 2020 has already delivered its report.

The panel recommended taxes on carbon emissions and international transport, including air tickets.

Orr said no one should expect "the final deal" in Cancun.

But he said: "The time has come for some decisions on issues and therefore we do want some concrete results."