The naturalist said that it was "silly" to play down the issue of climate change in an interview with Sky News.
The 88-year-old said: Wherever you look there are huge risks. The awful thing is that the people in authority and power deny that when the evidence is overwhelming.
"They deny it because it's easier to deny it.
"It's a very major, serious problem facing humanity but at the same time it would be silly to minimise the size of the problem.
"Never in the history of humanity in the last 10 million years have all human beings got together to face one danger that threatens us.
"It's a big ask but the penalty of not taking notice is huge."
One essential letter combination is missing from Sir David´s already impressive list - GWA (for global warming alarmist).