The Latest | UN Climate Summit

Alok Sharma, the British official who chaired last year's climate talks in Glasgow, declined to comment on criticism of the Egyptian presidency but made clear that an ambitious outcome to combat climate change was crucial.

"Every presidency runs things in their own way," he said. "The key issue for me and for the UK is that what we have here at the end of the day is a balanced and ambitious text across all the key pillars," he said.

"For us it's also vitally important to not just preserve what we agreed in Glasgow but that we build on that as well," said Sharma, referring to the recommitment made last year to limiting warming to 1.5 degrees Celsius (2.7 Fahrenheit) and a pledge to increase efforts to slash emissions cuts.

___ Spain's environment minister said they are willing to walk out if they can't reach a fair deal at the UN climate talks.

"We could be exiting of course," said Teresa Ribera. "We won't be part of a result that we find unfair and not effective to address the problem that we are handling, which is climate change and the need to reduce emissions." Ribera said she is "concerned" that a draft of the final document may not include a mention of the 1.5 degrees Celsius (2.7 degrees Fahrenheit) warming limit target set in Paris in 2015.

She added she didn't want to see a result "that may backtrack what we already did in Glasgow," referring to the renewed commitment to the 1.5 C goal at the climate summit last year.

"That's something that we'd like to see, that there is a strong commitment to the 1.5 targets," said Teresa Ribera.

On the role of the presidency, Ribera said that the process has been "very confusing." "It is not clear … and we are running out of time," she said.