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.”