A DIRE warning about the need to mitigate man-made global warning from a Vatican-appointed panel of scientists has not yet convinced Australia's highest-ranking Catholic, who said the causes of climate change were "unclear".

A report released this month by the Pontifical Academy of Sciences called on "all people and nations to recognise the serious and potentially irreversible impacts of global warming" caused by man-made greenhouse gas emissions.

Cardinal Pell ...agnostic on climate change causes. Credit:AFP

"By acting now, in the spirit of common but differentiated responsibility, we accept our duty to one another and to the stewardship of a planet blessed with the gift of life," it read.

The Archbishop of Sydney, Cardinal George Pell, said he would study the document carefully but questioned the effectiveness of any action.