TONY Abbott is under pressure to justify a claim to primary school students that it was considerably warmer when Jesus was alive than it is today.

The Opposition Leader urged year 5 and 6 students at Trinity Gardens Primary School in Adelaide to be sceptical about the human contribution to climate change, saying it was an open question.

During a question-and-answer session on Friday, Mr Abbott said that it was warmer ''at the time of Julius Caesar and Jesus of Nazareth'' than now.

Leading scientists said there was no evidence to suggest the globe was hotter 2000 years ago. Australian Academy of Science president Kurt Lambeck said true scepticism was fine, but required looking at published data with an open mind.

''To make these glib statements to school students, I think, is wrong,'' Professor Lambeck said.