Johnson made the mistake during a special press conference, in which he spoke alongside COP26 president Alok Sharma.
He was asked about the reaction that António Guterres, Secretary-General of the United Nations, had to the final outcome of the climate talks. In response, Johnson said: “I don’t think Antonio would want people to think that we’ve cracked it here at COP in Edinburgh, of course not.”
Following this comment, which was broadcast live on the BBC, Johnson was mocked online for his mistake.
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During the press conference, The Prime Minister also said that COP26 “sounded the death knell for coal power”, but his delight at any progress made at the Glasgow summit is “tinged with disappointment”.
He hailed the “truly historic” outcome of the summit, describing the agreement as “game-changing”, but acknowledged not all countries were willing to meet the level of ambition expected by many.
However, Johnson insisted the aim of keeping global temperatures from rising above 1.5C is “still alive”.
On Saturday, Cop26 President Alok Sharma was close to tears on a couple of occasions during an hours-long final plenary, including as he apologised to delegates for the way a change to the pact’s wording on fossil fuels was brought about at the eleventh hour.
Following a push led by China, and backed up by India, it was decided to change the language from accelerating the “phase out” of unabated coal to “phase down”, a move that prompted angry responses from European and vulnerable countries.
However, on Sunday, Mr Johnson said the watered-down language in the Glasgow Pact’s coal pledges do not “make that much of a difference”.
He said: “It’s an immense thing to get a commitment from 190 countries to phase down or phase out coal.
“Whether the language is phase down or phase out doesn’t seem to me as a speaker of English to make that much of a difference. The direction of travel is pretty much the same.”