Boris Johnson will issue a rallying call to not to allow “defeatism” in the face of the worsening economic situation to undermine the fight against global warming.

The former prime minister, who is attending the Cop27 climate change summit in Egypt, will warn on Monday a “corrosive cynicism” is jeopardising efforts to wean the world away from fossil fuels.

In a rare public intervention since being ousted from No 10 earlier this year, he will insist it is still possible to achieve the goal of limiting temperature rise to 1.5C – avoiding the worst effects of climate change.

“Because the spike in oil and gas prices – and the consequent global inflation, the hikes in the cost of fertiliser and food have had an impact here and everywhere, they have led some naysayers to a corrosive cynicism about net zero,” he will tell a Climate Forward event organised by The New York Times.

“We must end the defeatism that has crept in since last year, we must end Putin’s energy blackmail, we must keep up our campaign to end global dependence on hydrocarbons, and if we retain the spirit of creative and promethean optimism that we saw at Paris and Glasgow, then we can keep 1.5 alive.”

Mr Johnson emerged as an enthusiastic champion of the net zero agenda at last year’s Cop26 summit in Glasgow, having in the past been sceptical about green issues, and his appearance in Sharm El-Sheikh is an indication of his determination to keep its legacy alive.

It comes two weeks after he abandoned an attempted return to No 10 after he failed to persuade Rishi Sunak to join him on a joint ticket following the resignation of Liz Truss – paving the way for the former chancellor to become prime minister.

Mr Sunak is also in Egypt for the opening day of the conference – although it is unclear whether the two men will meet.

Speaking to The Sun on the flight out, Mr Sunak said he hoped he would “bump into him” at some point.

“Isn’t it great we have a PM and a former PM both at Cop? That says something special about our country,” he said.

“Boris has been a stalwart champion of building a greener future, he deserves praise and credit for that, its great that he’s there.”

Nevertheless, there is likely to be some nervousness among the Prime Minister’s entourage that Mr Johnson may seek to upstage his first appearance on the world stage since entering No 10.

In an interview with The Times on Saturday, Mr Sunak insisted their talk about the leadership had been “cordial”, despite his role earlier this year in bringing Mr Johnson down.

“We worked very closely with each other for a long time, I have an enormous amount of affection and respect for him,” he said.