John Kerry, the US secretary of state, has said governments trying to reach a climate agreement in Paris face a tough fight in the 72 hours remaining to reach a deal.
The talks move into the endgame on Wednesday, when the French hosts produce a new draft text for review by the 195 assembled countries.
French officials have said the talks will end with a strong outcome and on time on Friday – although climate negotiations typically run over into the early hours of Saturday and even Sunday.
But Kerry said governments face a tough slog to reach a deal.
“I think consensus is slowly being built. There will be differences tomorrow. Some of them will be sharp, and that is where your final stage fight will be beginning, but I think there is a growing feeling of possibility,” Kerry told a small group of reporters.
The challenge of reaching an agreement has now been handed off from negotiators to ministers and cabinet officials like Kerry.
When the talks got underway at the start of the week, the 48-page draft text was littered with more than 900 sets of brackets indicating areas of disagreement – which is considered a relatively positive position for a climate negotiation.
After mainly upbeat statements from US and European officials, Kerry offered a fairly sober view of the prospects for an agreement in Paris that would ensure that future warming remains below dangerous levels.
Kerry indicated some areas of emerging agreement. After meetings with leaders of Tuvalu and other small islands most vulnerable to climate change, he said that the US was inclined to support their demands to set a goal of limiting warming to 1.5C. However, he described the target as an add-on to the agreement, and more of an aspiration than a must-do.
“I think you can write that aspiration into the agreement in a way that doesn’t make it the target or guidepost for the agreement,” Kerry said.
Even after lengthy negotiations, conducted by smaller working groups huddled behind closed doors, a number of stumbling blocks to an agreement remain – the main one being the division of responsibility between rich and poor countries for cutting emissions.
But Kerry rejected a key argument from developing countries that the current structure of the deal – that was widely influenced by the US – did not adequately reflect those different economic histories. “The entire agreement is based on differentiation,” he said.
Other obstacles to a strong deal remain, Kerry said. He accused unnamed countries of getting in the way of a deal.
“I think there are a few countries that wouldn’t mind coming out of here with a minimalist consequence and result and I think the verdict is very much out on what is manageable there,” Kerry said. “We just have to see where the text emerges before we really know how the lines are drawn.”
As the talks move towards the finish, China, Brazil and South Africa joined India in rejecting a key OECD study saying that rich countries have already mobilised two-thirds of the $100bn (£67bn) pledged to secure a new climate deal.
Their stand suggests that finance will continue to be a big sticking point in the negotiations.