The 86-year-old, who has made protecting the environment a cornerstone of his 10-year papacy, had planned to become the first pontiff to attend the UN event since the process began in 1995.
"Although the Holy Father's general clinical picture has improved with regard to his flu-like condition and inflammation of the respiratory tract, doctors have asked the Pope not to make the trip planned for the coming days to Dubai," Vatican spokesman Matteo Bruni said in a statement.
"Pope Francis accepted the doctors' request with great regret and the trip is therefore cancelled," Bruni said.
Bruni -- who just hours earlier had told a briefing that the pope would be attending -- added that the pope still wished to be part of discussions in Dubai, without specifying.
With Francis's withdrawal from the conference, which begins Thursday, COP 28 will lose one of the highest profile advocates of the environment, a moral authority recognisable on the global stage whose words some believed could nudge leaders to take concrete action.
- Touch of flu -
Francis, who turns 87 next month, has suffered a series of health issues in recent years, from knee and hip pain to an inflamed colon and most recently, hernia surgery in June.
On Saturday, he cancelled events due to what the Vatican called "light flu symptoms". It said that a CT scan had ruled out "risks of pulmonary complications".
The pope was forced to recite the traditional Angelus prayer on Sunday from his residence rather than overlooking St Peter's Square.
But Bruni said the pope would lead his weekly audience on Wednesday morning as planned.
The leader of 1.3 billion Catholics, more than half of whom live in the developing world, Francis has long insisted on the link between climate change and poverty, with the world's most marginalised paying the highest price for global warming.
In Dubai, the pope was expected to use the platform to castigate countries for a lack of action on climate change, and seek to persuade them to dramatically cut their greenhouse gas emissions.
He was also expected to play a role in rebuilding trust between climate-vulnerable nations and rich, consumerism-driven polluters.
- 'Breaking point' -
Francis's address to world leaders at COP28 would have come just weeks after he published a text in October warning that the world was "collapsing" and near the "breaking point" due to global warming.
That warning -- which expressed frustration at inadequate responses by governments to the climate crisis -- was a follow-up to his seminal 2015 thesis on the environment "Laudato Si" (Praise Be To You), a passionate critique of manmade climate change and its repercussions across the globe that relied on science.
It is believed to have helped contribute to a breakthrough in UN climate talks in Paris a few months later, when countries committed to limit warming to "well below" two degrees Celsius above pre-industrial levels, and preferably the safer 1.5C limit.
Francis wrote in October that the COP 28 talks could "represent a change of direction" if participants were to make binding agreements on moving from fossil fuels to clean energy sources such as wind and solar.
The talks will draw up the first official assessment of humanity's efforts to respect the 2015 agreement and its ambition to limit global warming "if possible to 1.5 degrees Celsius" since the pre-industrial era.
Besides addressing world leaders, Francis was expected to inaugurate the first-ever faith pavilion at COP, in a sign of the growing engagement of religion in climate issues.
Sverker Sorlin, a specialist in global environmental governance at the KTH Royal Institute of Technology in Stockholm told AFP before the pope cancelled that his presence at COP represented a "tipping point".
"The pope may not turn the tables at the meeting, but be a 'tipping point' that may nudge and push the negotiators... in the right direction," said Sorlin, calling Francis' personal engagement on climate change "of tremendous importance."
Last year, knee pain caused Francis to postpone a trip to the Democratic Republic of Congo and South Sudan. He made the visit earlier this year.
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