Boris Johnson has declared he is “cautiously optimistic” about a deal at Cop26 to keep global temperature rises below 1.5C as he urged China to commit to bringing emissions down by 2025.

The prime minister had previously said the world would be 5-1 down in a football match when it came to the 1.5C target but he said on Monday that the score was now more like 5-2 or 5-3.

He claimed there had been a turnaround since the G20 leaders’ summit at the weekend, arguing that a commitment from Brazil on halting deforestation, the Indian pledge on decarbonising power by 2030 and extra cash promised by Japan were good signs.

However, he said there was still a “very long way to go” before a deal to keep 1.5C alive was achieved. Experts have said that reductions of 28 gigatonnes of emissions by 2030 are necessary to meet that target but pledges so far do not add up to anywhere near that amount.

Johnson said talks with China, the world’s biggest emitter, were now focussed on trying to persuade its negotiators to bring forward its pledge for its emissions to peak in 2030 by five years.

“You bet we need more progress from China … and everyone here at this gathering,” he told a press conference in Glasgow. “The question is how much before [2030]. That’s the issue. There’s a world of difference between peaking in 2030 … and peaking in 2025. That’s where we’re keeping the pressure up.”

Johnson said another area of pressure was asking developed countries to contribute more in climate finance for developing countries, saying they are going to “have to do more”. UK government sources have acknowledged this is the most difficult area of negotiation and where Cop is likely to fall short.

The prime minister said commitments from countries would be “100% useless if the promises are not followed up with action”. Asked about concern among voters about the cost of net zero, Johnson said people had to realise that failing to tackle the climate crisis would be an “economic catastrophe”.

“I happen to think that there’s a great wisdom in the British people and I think that they can see that this is an issue that needs to be fixed and they may not listen to me, but they certainly listen to Sir David Attenborough and they look at what’s actually happening around the world,” he said.

“They look at the fires, they look at the floods, and they look at the hurricanes, and the increased incidence of all three, much-increased incidence, and they think something’s happening here.”

“They’re not dumb and they can see that this is something that needs to be tackled,” he added, while ruling out a referendum on the push for net zero.

Johnson’s demeanour was more upbeat than at the G20 summit, when he warned of a serious risk of failure in Glasgow. His official spokesperson dismissed the idea that the prime minister had deliberately lowered expectations to later declare his negotiations with other world leaders in Glasgow a success.

Asked whether Johnson’s weekend gloom had been expectation management,
the spokesperson said: “The PM felt very much at the G20 that limited progress was made but was by no means the significant boost that was needed. What we’ve seen so far is some early signs that we are starting to make some progress. Again, we are not complacent. This is not a done deal by any means. There is a huge amount of work left to do.”

Johnson has still not made a decision on whether to come back at the end of Cop26, and could instead make a statement from Downing Street on what is agreed.