Boris Johnson has been pictured using a no-frills airline to travel to Cop27.
The former prime minister was seen on a Pegasus Airlines flight to Egypt via Istanbul on Sunday.
Mr Johnson spoke on the fringes of the summit on Monday where he urged leaders “not to go weak on net zero”.
“The reason I’m here is because the discussion about Ukraine is having all kinds of negative effects,” he said. “This is not the moment to go weak on net zero, this is the time to double down.”
Mr Johnson insisted he wanted to play a supportive role to UK Prime Minister Rishi Sunak, but said he would act as the guardian of the commitments made when he was leader at Cop26 in Glasgow.
Mr Sunak made a late about-turn to attend the conference, having previously suggested he would be too busy dealing with the domestic economic problems.
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”.
“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,” he said.
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 Russia’s invasion of Ukraine, with countries questioning the goal of cutting emissions at a time of soaring energy prices.
This year, the summit will be focusing on four areas of the climate crisis: mitigation, adaptation, finance and collaboration.
Cop26, which took place last year in the Scottish city of Glasgow, resulted in the Glasgow Pact, which committed participants to lower carbon emissions.