Kerry says US and China must 'win climate battle' together

"Without China and the United States aggressively moving forward to reduce emissions, we don't win this battle," the former secretary of state told reporters on the eve of the opening of COP28.

"We are number two (biggest emitter), they're number one... So we have decided to actually work together to get a successful COP," said Kerry, who mentioned his last meeting with China's long-standing climate envoy Xie Zhenhua earlier this month.

He said both countries -- who produce 40 percent of all greenhouse gases -- "need to step up and help get the job done at a faster rate" to limit warming to 1.5 Centigrade as was agreed at the Paris climate talks in 2015.

China is the world's biggest greenhouse gas emitter. But when past emissions are taken into account, it is second behind the US.

Fatih Birol, the head of the International Energy Agency (IEA), told AFP in September that he was appealing to both superpowers to put aside "their economic and geopolitical tensions" during the talks.

After months of discreet discussions, both countries released a joint climate statement in which they announced cooperation in various areas including on methane, the second most damaging greenhouse gas after CO2. It also mentioned common objectives from COP28.

The first official audit of the Paris agreement, which has to be agreed by consensus, is one of the most anticipated decisions due to be taken in Dubai.

"This global stocktake needs to earn the credibility of the world by being candid, strong, visionary and comprehensive," added Kerry.

He said the US would push for a "commitment to accelerate the phase out of unabated fossil fuels", meaning without carbon capture -- a key battleground at the talks.

"I feel confident that we're going to make progress. The question is how much progress," he added. "The proof is in the pudding."