(ANSA) - Rome, December 18 - The United Nations climate change summit in Copenhagen headed towards its conclusion on Friday with world leaders seeking a compromise on emissions targets, but no binding treaty.

Earlier in the day, the Vatican envoy to the UN, Msgr.

Celestino Migliore predicted meagre results from the summit, saying ''massive international meetings had outworn their usefulness as a format for addressing the world's problems''.

The Papal nuncio said the summit was hamstrung from the outset by disagreement over ''what is causing climate change and how to stop it''.

''Without consensus for the diagnosis, it's going to be hard to agree on a cure,'' he said.

Migliore also underlined the ''all too familiar problem of how and in what measure to help developing countries''.

''Should they be given money outright, or should rich countries subsidize individual projects?'' he asked.

''The question is how to keep these funds from falling into the wrong hands''.

Migliore said ''large international summits worked well in the 1990s, when they were something of a novelty, but the mechanism has grown outdated''.

Pointing to a long-running debate on reforming the UN Security Council, Migliore said ''it's hard enough to get 15 parties to agree,'' let alone the nearly 200 national delegations present in Copenhagen.

He said that the system needed to be ''streamlined and revitalized to keep national interests from getting in the way of much needed progress''.

Delegates in Copenhagen worked through the night on Thursday to outline a 13-point agreement in a last-ditch attempt to salvage the conference in its final hours.

The draft proposed $30 billion between 2010-2012 towards stopping temperatures from rising more than two degrees Celsius above pre-industrial levels, but left values for emissions cuts blank in the hopes world leaders would step into fill them.

US President Barack Obama made his much awaited appearance at the summit on Friday attempting to rally delegates with the promise of $100 billion to help developing countries.

''Now I believe it's the time for the nations and the people of the world to come behind a common purpose. We are ready to get this done today, but there has to be movement on all sides,'' he said.

But the president met with lukewarm applause from an audience hoping he would lead the way with a commitment for new emission targets inciting other big polluters to follow his example.

Speaking at the plenary session ahead of Obama, Chinese Premier Wen Jiabo assured delegates that ''China takes the issue of climate change seriously''.

But he underlined the ''historic responsibility'' of the US and other countries for climate change, which he said far outweighed that of developing countries like China.

The US and China together produce over half the world's greenhouse gas emissions, making their cooperation a vital part of an eventual deal.

After addressing the assembly, the two leaders met for bilateral talks aimed at saving the conference with a deal allowing them to walk away from the summit having made significant progress towards establishing a new protocol.

Diplomatic sources said the new accord could include targets as high as 50% for C02 emissions by 2020, though Chinese delegates are reportedly unwilling to sign onto cuts any larger than 30%. The deal would lay the foundations for another climate summit in Bonn next June with the objective of turning the targets into a binding agreement.