ABOARD THE PAPAL PLANE (WASHINGTON POST) Pope Francis said Monday (Sept 11) that US President Donald Trump should allow young immigrants to stay in the United States if he is truly "pro-life".

"I have heard it said that the president of the United States presents himself as a man who is pro-life, and if he is a good pro-life (man) then he will understand that the family is the cradle of life, and that it must be defended as a unit," Francis said, in response to a question about Trump's decision to discontinue the Deferred Action for Childhood Arrivals program (DACA) that allowed immigrants brought to the United States as children to live and work or study in the US. The pope's comments were reported by America magazine.

In the same conversation with reporters, aboard a plane leaving Colombia after a five-day trip to his native South America, Francis returned to the subject of climate change, a favourite for the wonky pontiff who was a scientist early in his career. Anyone who doubts that the climate is changing should listen to scientists, who "speak very clearly", he said.

Francis has a long habit of making some of his most pointed political comments while giving news conferences on his plane flights. It was on a plane during the 2016 election campaign that the pope said that Trump's plan of building a wall on the Mexican border "is not Christian".

Despite tension over that remark and subsequent differences of opinion, Francis and Trump met at the Vatican in May - and Francis pushed the issue of climate change in person, handing Trump a copy of his own science-laden encyclical about the moral responsibility to protect the environment, just as Trump was mulling his eventual decision to pull out of the Paris climate accord.

On DACA, Francis said that he would like to study the American policy more thoroughly, but he is troubled by the possibility of young immigrants in any nation being compelled to move away from their families. He expressed interest in Congress extending what Trump has ended, saying he has "hope that it can be rethought a little".