COPENHAGEN - U.N. talks billed as a turning point in a bid to slow global warming open on Monday seeking to agree curbs on greenhouse gas emissions and raise billions of dollars for the poor in aid and clean technology.

The two-week talks, ending with a summit of 105 world leaders including U.S. President Barack Obama on December 18, will have to overcome deep distrust between rich and poor nations about sharing out the burden of costly curbs on emissions.

The planned attendance of the leaders and pledges to curb emissions by all the top emitters -- led by China, the United States, Russia and India -- have raised hopes for an accord after sluggish negotiations in the past two years.

Copenhagen is already a turning point in the international response to climate change, said Yvo de Boer, head of the U.N. Climate Change Secretariat.

South Africa added new impetus on the eve of the event, saying on Sunday it would cut its carbon emissions to 34 percent below expected levels by 2020, if rich countries furnished financial and technological help.

World leaders did not attend the last time the world's environment ministers agreed the existing U.N. climate pact, the Kyoto Protocol, in 1997. Copenhagen will be the biggest climate meeting in history with 15,000 participants from 192 nations.

In a conference hall with wind turbines outside generating clean energy, Danish Prime Minister Lars Lokke Rasmussen and Rajendra Pachauri, head of the U.N.'s panel of climate experts, will be among speakers at Monday's opening session.

Plans by world leaders to attend have brightened hopes since Rasmussen said last month that time had run out to agree a full legal treaty in 2009. The aim for Copenhagen is a politically binding deal and a new deadline in 2010 for legal details.

Some 56 newspapers from 45 countries including The Guardian, Le Monde, El Pais and Toronto Star published on Monday a joint editorial urging rich and poor to unite in Copenhagen.

At the deal's heart must be a settlement between the rich world and the developing world, it said. Social justice demands that the industrialized world digs deep into its pockets. Many of us, particularly in the developed world, will have to change our lifestyles.

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The existing Kyoto pact obliges binds industrialized nations to cut emissions until 2012 and even its supporters admit is only a pinprick in rising world temperatures, especially since Washington did not join its allies in ratifying the pact.

This time, the idea is to get action from all major emitters including China and India to help avert more droughts, desertification, wildfires, species extinctions and rising seas.

The meeting will test how far developing nations will stick to entrenched positions, for example that rich nations must cut their greenhouse gases by at least 40 percent by 2020 -- far deeper than targets on offer.

De Boer wants developed nations to agree deep cuts in greenhouse emissions by 2020 and come up with immediate, $10 billion a year in new funds to help the poor cope. And he wants developing nations to start slowing their rising emissions.

It needs to be new money, real and significant, he said.

De Boer said that Pachauri on Monday would address a scandal about leaked e-mails from a British university that skeptics say show that some researchers exaggerated evidence for warming.

But he said the U.N. process of reviewing climate science was well insulated against manipulation.

I do not believe there is any process anywhere out there that is that systematic, that thorough and that transparent, he said.

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