The prime minister had been under growing pressure to U-turn after his predecessor Boris Johnson confirmed he would be going to the event at Sharm el Sheikh.
In apparent dig at the new PM, Mr Johnson said it had “become unfashionable” to talk about the sucesses of the previous Cop26 meeting held in Glasgow.
On Wednesday Mr Sunak tweeted: “There is no long-term prosperity without action on climate change. There is no energy security without investing in renewables.”
He added: “That is why I will attend Cop27 next week: to deliver on Glasgow’s legacy of building a secure and sustainable future.”
No 10 previously said Mr Sunak was not expected to attend “due to other pressing domestic commitments”, despite the UK handing over presidency to Egypt for the 6 to 18 November summit.
But by Monday a No 10 spokesperson said the position was “under review”, before Mr Sunak announced the change on Wednesday.
Labour leader Angela Rayner said the PM had been “dragged kicking and screaming into doing the right thing” after he committed to attend the Cop27 climate summit. “Embarrassing,” she added.
Labour’s shadow climate secretary Ed Miliband said Mr Sunak was a “phony” following his U-turn. “Sunak on Thursday: I can’t possibly go to Cop. Sunak six days later: I can’t possibly not go to Cop. The guy is a phoney.”
Liberal Democrats’ climate spokesperson Wera Hobhouse said Mr Sunak was “only going after being embarrassed by Boris Johnson’s attendance” and said the UK needs “action” from the PM.
Green MP Caroline Lucas – who had said she hoped Mr Johnson would “embarrass” Mr Sunak into going – said she was “glad to see Sunak’s screeching U-turn on Cop27”.
She added: “But what an embarrassing mis-step on the world stage. Let this be a lesson to him – climate leadership matters. Now he urgently needs to increase UK ambition on emission reduction targets and pay what we owe to global climate funds.”
Mr Sunak’s initial decision to avoid the summit raised eyebrows. His predecessor Liz Truss was set to go and Scotland’s first minister Nicola Sturgeon is also attending, along with US president Joe Biden, France’s Emmanuel Macron and other world leaders.
Mr Johnson, ousted in the summer after Mr Sunak and other ministers resigned, told Sky News that he would be going, and desribed the summit hosted in the UK as a “fantastic global success” which did “a huge amount of good for the planet”.
Cop26 president Alok Sharma said he was “delighted” at the new prime minister’s U-turn over Cop2, after saying he was “disappointed” over his planned failure to attend.
The outgoing climate minister also said the Sunak government should think again about plans to open Britain’s first new coal mine in a generation in Cumbria.
Mr Sunak said “a significant proportion of this coal that’s generated would be exported”, telling Politico: “My personal opinion on this is that I think if this is about creating jobs, then … you can create a lot more jobs doing this in green sectors.”
The Cop27 decision is not the first climate U-turn from Mr Sunak. The PM announced last week that the ban on shale gas fracking will be reinstated, reversing a policy launched by Liz Truss’s short-lived government.
Lord Deben, the government’s top adviser as chair of the Climate Change Committee, told The Independent at the weekend that Britain’s climate leadership was falling short on multiple fronts.
Britain’s own bid to tackle emissions was “off track”, said Lord Deben, adding that the turmoil at the top of government had meant that the UK had failed to lead “anybody” on the issue in recent months.
Activist Greta Thunberg said she would not be going to Cop27 because of the country’s record on human rights record.
She also dismissed the annual UN conference as an opportunity for leaders to indulge in “greenwashing, lying and cheating”.
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