PARIS (Reuters) - World population growth is a bigger problem than climate change, French presidential candidate Nicolas Sarkozy said on Thursday, pouring more fuel on a fire he ignited this week when he appeared to downplay man-made climate change.

Sarkozy, acknowledging on a late night TV talk show that climate change was "a very serious challenge" said that: "the real challenge is that of demographic change."

Earlier this week, the former head of state who is running for the center right Les Republicains party nomination, was quoted in a weekly publication as saying "only man could be so arrogant to think that it is us who is changing the climate."

His mainstream conservative rival, former prime minister Alain Juppe, went on the attack after Sarkozy's first comments, saying the former leader was in denial of reality.

"The first cause of environmental degradation... is the number of people on the planet," Sarkozy said.

(Reporting by Bate Felix; Editing by Richard Lough)