Boris Johnson warned Tories against going soft on climate change targets as he suggested that rising temperatures in Westminster may have contributed to his ousting.

The former prime minister dismissed the “nonsense” of calls to resume fracking and return to fossil fuels in response to the soaring energy prices triggered by Vladimir Putin’s invasion of Ukraine.

Mr Johnson, who was speaking on the fringes of the Cop27 climate summit in Egypt, insisted he wanted to play a supportive role to Rishi Sunak, but said he would act as the guardian of the commitments made when he was prime minister at Cop26 in Glasgow.

Mr Sunak made a late U-turn to attend the conference in Sharm El-Sheikh, having previously suggested he would be too busy dealing with the domestic economic problems in the UK.

Mr Johnson said he was glad Mr Sunak was at the summit, telling his audience at a New York Times event: “I’m a foot soldier, a spear carrier. I’m here in a purely supportive role and to remind the world what we did at Glasgow.”

He said the present government “understands that and wants to take it forward”.

Mr Johnson continued: “The PM is here. I’m glad he is here. He made an outstanding speech the other day, he is on absolutely the right lines.”

The former prime minister said he was at the summit to warn “the risk is some people will go weak and wobbly on net zero, we can’t have that”.

He warned the fight against climate change had become one of the “collateral victims” of Mr Putin’s invasion of Ukraine, with countries questioning the goal of cutting emissions at a time of soaring energy prices.

In a swipe at Tories – including successor Liz Truss – he warned against calls to revive fracking, the process of extracting shale gas, in the UK.

Ms Truss had planned to lift the ban on fracking in England, but Rishi Sunak reinstated it.

“There are people who have drawn the conclusion that the whole project of net zero needs to be delayed, mothballed and put on ice – for instance we need to reopen coal-fired power stations and frack the hell out of the British countryside,” he told a Cop27 fringe event.

The former prime minister said the summit in Egypt was a time to “tackle this nonsense head on”.

“Yes, of course, we do need to use hydrocarbons in the transitional period and, yes, in the UK there is more that we can do with our own domestic resources,” he said.

“However, this is not the moment to abandon the campaign for net zero, this is not the moment to turn our backs on renewable technology.”

Meanwhile, Mr Sunak insisted he believes it is “great” that his predecessor in No 10 was also at the summit.

“Oh, it’s great that the former prime minister is here,” Mr Sunak told broadcasters.

“And I think it says something great about the UK that not only have we got the current Prime Minister here, we’ve got a former prime minister here.

“It just demonstrates our leadership on this issue globally. And Boris was a stalwart champion of building a greener future. He deserves enormous credit and praise for that.”