Christian charities and climate campaigners have expressed disappointment after the Vatican said the Pope wouldn't be travelling to the COP28 conference this week.
Francis, who is nearly 87, is suffering from flu and lung inflammation.
He was due to travel to the conference in Dubai for three days on Friday.
In a statement last night the Vatican said:
"Although the Holy Father's general clinical condition has improved with regard to the flu and inflammation of the respiratory tract, doctors have asked the Pope not to make the trip planned for the coming days to Dubai."
It added that the pope had agreed not to travel "with great regret," but that it would look into ways that the leader of the world's Roman Catholics could contribute to the discussions remotely.
Peter Williams from Catholic Voice told Premier Christian News:
“I’m not massively surprised, as he is 86. The Vatican will be worried about pneumonia at this point, because when he was 21 he had part of his lung removed so he only has one workable lung. So for all these reasons, they're being extremely cautious, and rightly so.
“I think his general condition means they are very, very cautious about him going somewhere like Dubai, and engaging in a three-day visit like that, based on not just the stress of travel, but the change in the climate. All of this when you're that old and you are that frail, that's something which they'd be very cautious about.”
In a briefing earlier this week, Vatican spokesperson Matteo Bruni had said Francis would deliver one of the keynote speeches in Dubai on Saturday and have bilateral meetings the same day with about 30 people, including about 20 heads of state.
The pope has made protection of the environment one of the cornerstones of his pontificate.
In a document issued in October, Francis had appealed to climate change deniers and foot-dragging politicians to have a change of heart, saying they cannot gloss over its human causes or deride scientific facts while the planet "may be nearing the breaking point".
Responding to the news that the Pope wouldn’t be attending COP28 in person, CAFOD’s Director of Advocacy, Neil Thorns, said:
"We hope that countries at COP28 will live up to Pope Francis’ urgent call for greater ambition on addressing the climate crisis, and for politicians to leave a legacy they can be proud of.
“We hope he recovers soon and will continue to encourage leaders from Rome.”