The Vatican, which under Pope Francis' insistence has strongly backed the Paris climate change deal, would see a US exit as a slap in the face and a "disaster for everyone," a senior official says.
At their meeting last month, the pope gave US President Donald Trump a signed copy of his 2015 encyclical letter that called for protecting the environment from the effects of climate change and backed scientific evidence that it is caused by human activity.
Vatican Secretary of State Cardinal Pietro Parolin urged Trump in a separate meeting not to quit the Paris accord.
"If he really does (pull out), it would be a huge slap in the face for us," said Bishop Marcelo Sanchez Sorondo, head of the Pontifical Academy of Sciences, which has hosted numerous international conferences on climate change.
"It will be a disaster for everyone," he told the Rome newspaper La Repubblica. In a telephone call with Reuters, Sanchez Sorondo confirmed the comments in the newspaper.
Trump is due to announce his decision later on Thursday US time.
A source briefed on the decision has told Reuters in Washington that he will follow through on his campaign pledge to leave the global agreement.
