One of the world's leading naturalists has accused U.S. politicians of ducking the issue of climate change because of the economic cost of tackling it and warned that it would take a terrible example of extreme weather to wake people up to the dangers of global warming.

Speaking just days after the subject of climate change failed to get a mention in the U.S. presidential debates for the first time in 24 years, Sir David Attenborough told the Guardian: "[It] does worry me that the most powerful nation in the world ... denies what the rest of us can see very clearly [on climate change]. I don't know what you do about that. It's easier to deny."

Asked what was needed to wake people up, the veteran broadcaster famous for series such as Life and Planet Earth said: "Disaster. It's a terrible thing to say, isn't it? Even disaster doesn't do it. There have been disasters in North America, with hurricanes and floods, yet still people deny and say 'oh, it has nothing to do with climate change.' It visibly has got [something] to do with climate change."

But some U.S. politicians found it easier to deny the science on climate change than take action, he said, because the consequence of recognizing the science on human-made climate change "means a huge section from the national budget will be spent in order to deal with it; plenty of politicians will be happy to say 'don't worry about that, we're not going to increase your taxes.'"

Neither Barack Obama or Mitt Romney mentioned climate change in three TV debates, despite a summer of record temperatures and historic drought in the U.S.