Pope Francis has opened his visit to the United States with a call for action to combat climate change.
Speaking in front of a crowd of thousands at the White House, the Pope called climate change a problem that "can no longer be left to a future generation".
US President Barack Obama hailed the pontiff as a moral force who is "shaking us out of our complacency" with reminders to care for the poor and the planet.
Francis delivered a strong message against those who doubt the science of climate change, saying that the warming planet "demands on our part a serious and responsible recognition" of conditions awaiting today's children.
The Pope's message also had something for conservatives, with a call to protect religious liberties - "one of America's most precious possessions".
"All are called to be vigilant,' he said, "to preserve and defend that freedom from everything that would threaten or compromise it."
The message is expected to be welcomed by many US bishops and conservatives who have objected to the Obama administration's healthcare mandate and the recent Supreme Court legalisation of same-sex marriage.
The Pope and president stood on a red-carpeted platform decorated with red, white and blue bunting, standing at attention for the national anthems of the Holy See and the United States.