TONY ABBOTT is under pressure to justify telling students it was considerably warmer when Jesus was alive after leading scientists said his claim was wrong.

He urged year 5 and 6 pupils at an Adelaide school to be sceptical about the human contribution to climate change, saying it was an open question.

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In a question-and-answer session on Friday, the Opposition Leader said it was warmer "at the time of Julius Caesar and Jesus of Nazareth" than now.

Leading scientists said there was no evidence to suggest it was hotter 2000 years ago.