The prime minister has reversed an earlier decision not to go to the COP27 climate summit in Egypt.
No 10 had said Rishi Sunak was too busy preparing for the 17 November budget to attend the event which opens on Sunday.
But this had been widely criticised by climate campaigners, opposition parties and climate adviser Alok Sharma.
Mr Sunak said there was "no long-term prosperity without action on climate change" or energy security without investment in renewables.
"That's why I will attend COP27 next week - to deliver on Glasgow's legacy of building a secure, clean and sustainable future," he told MPs during Prime Minister's Questions.
On Tuesday, former prime minister Boris Johnson said he would attend COP27 in Sharm El Sheikh.
The UK hosted last year's COP (Conference Of The Parties) in Glasgow and it was chaired by Mr Sharma.
Green MP Caroline Lucas welcomed what she called a "screeching U-turn" after "an embarrassing mis-step on the world stage".
"Let this be a lesson to him - climate leadership matters," she added.
Labour leader Sir Keir Starmer accused the prime minister of acting "in the name of political management" rather than the national interest.
"Caving in to criticism is not leadership. Real leadership is seizing your seat at the table. For UK jobs. For clean energy. For our environment," he tweeted.
Liberal Democrat climate change spokesperson Wera Hobhouse said: "This whole debacle has shown the environment is simply not a priority for Rishi Sunak. He's only going after being embarrassed by Boris Johnson's attendance."
Foreign Secretary James Cleverly defended the prime minister's approach, saying he had always recognised COP27 was an "incredibly important event".
Mr Cleverly said Mr Sunak had wanted to make sure the economic situation was in hand, and had now reassured himself that was the case - freeing him up to travel to Egypt.
Mr Sharma, who had said he was "disappointed" Mr Sunak would not be attending, tweeted that he was "delighted" the prime minister would now be going.
Many world leaders including US President Joe Biden and France's Emmanuel Macron are due to attend the UN event.
Mr Sunak's predecessor Liz Truss had been set to go and Scotland's First Minister Nicola Sturgeon will also be there.
A number of countries had also criticised Mr Sunak's earlier decision not to go and questioned the UK's commitment to tackle the climate crisis.
The Egyptian government, which is hosting COP27, voiced its "disappointment". Carlos Fuller, Belize's ambassador to the UN, told The Guardian it looked as if the UK was "washing their hands of leadership".
Mohammed Nasheed, speaker of the Maldives parliament and a former president, said nothing was more serious than climate change.
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