The head of the Bureau of Meteorology has rebuked Cardinal George Pell for his scepticism about climate change, insisting the man has been misled.

Sydney's Catholic Archbishop is an outspoken disbeliever in man-made global warming, arguing that it was hotter during the Middle Ages and carbon dioxide levels are not historically high.

Bureau chief Greg Ayers used an appearance at a Senate estimates hearing yesterday to rip into the cardinal's personal views.

He said the core of his arguments were based on a book by Australian scientist Ian Plimer called Heaven and Earth: Global Warming the Missing Science.

But Cardinal Pell's convictions were misplaced, Dr Ayers said.