Ministers and negotiators from more than 75 nations made headway in talks ahead of a crunch UN climate summit but "the task ahead is considerable", France's foreign minister said Tuesday.
Laurent Fabius, who will preside over the November 30-December 11 conference in Paris, told journalists the three days of talks ending Tuesday had been an important step and "progress has been made on at least five points".
Nevertheless, he said, "the task ahead is considerable".
UN climate chief Christiana Figueres added: "It (Other OTC: ITGL - news) continues to be entirely possible to come to an agreement... despite all the challenges in front of us."
Fabius announced that 117 heads of state and government -- including US President Barack Obama, China's Xi Jinping, Narendra Modi of India and Russia's Vladimir Putin -- have confirmed they will attend the summit, tasked with inking a pact to stave off dangerous levels of global warming.
A rough draft of that hoped-for agreement has been drawn up by rank-and-file diplomats, with ministers set to sign the final deal at the end of the Conference of Parties (COP) in Paris.
The deal will be underpinned by national pledges to curb greenhouse gas emissions from burning fossil fuels blamed for climate change.
The "pre-COP" meeting sought to identify areas of potential compromise on issues still dividing nations, and thus avoid a repeat of the 2009 Copenhagen summit which ended without a binding global pact.
Fabius said there was momentum toward ensuring that countries ratchet up their efforts to slash carbon pollution beyond pledges submitted ahead of the summit.
"A review should take place every five years... to prepare an upward revision of national plans," he said.
Current national plans would yield average global temperatures three degrees Celsius above pre-industrial times -- far beyond the 2 C (3.6 degrees Fahrenheit) limit that scientists say is the threshold for dangerous warming.
"The COP21 will put in place the mechanism to close the gap," Manuel Pulgar-Vidal, Minister of Environment for Peru, told AFP. "Getting to 2 C depends on boosting our ambition."
Enshrining the principle that nations would not be allowed to "backtrack" on their carbon-cutting promises is also gaining ground, Fabius said.
Another make-or-break issue on the table in the three-day talks: chanelling money to developing nations to help them decarbonise their economies, and to shore up defences against unavoidable climate impacts.
"Climate finance was very central" to the discussions, said Thoriq Ibrahim, Minister of the Environment and Energy for the Maldives, one of many small island states whose very existence is threatened by rising seas.
"Adaptation is a matter of survival for us," he told AFP. "Nobody wants to leave the Maldives, we are there to stay."
The 195-nation UN climate forum has officially adopted the goal of limiting global warming to 2 C, but many vulnerable and poor nations are pushing for that threshold to be lowered to 1.5 C.
Recent scientific studies have shown that even if the 2 C goal is attained, the impact could be devastating in many parts of the world.
A 2 C spike would submerge land currently occupied by 280 million people, while an increase of 4 C -- humanity's current trajectory -- would cover areas home to 600 million, according to a study published by Climate Central, a US-based research group.