"There was a time in the 19th century when it was perfectly acceptable for civilised human beings to think that it was morally acceptable to actually own another human being for a slave", he said.
He said public attitudes on climate change and plastic waste had evolved similarly to those on slavery, which "totally transformed". "By the middle of the 19th century it was becoming intolerable".
The respected English broadcaster and natural historian who is famous for his documentaries including Life on Earth and Blue Planet, was invited to speak in front of the UK Parliament's British, Energy and Industrial Strategy Committee overnight about his views on climate change.
"Australia is already facing having to deal with some of the most extreme manifestations of climate change".
Attenborough is right. In the past century, Australia has experienced an increase of almost 1 °C in average annual temperatures, with several areas experiencing substantially reduced rainfall and a higher likelihood of extreme weather events such as drought or wildfires.More news: Amazon Extends 2019 Prime Day, But Is It Enough to Satisfy Customers?
"No one has done more to show the impact of man-made climate change on our planet", said Reeves.
"It had bleached white because of the rising temperatures and increasing acidity of the sea".
"I suspect that we are right now in the beginning of a big change".
"The most encouraging thing that I see, of course, is that the electors of tomorrow are already making themselves and their voices very, very clear", said Attenborough.
But there is also good news, Attenborough says.
Sir David backed the target to cut emissions to net zero by 2050, which the United Kingdom has now set in law, saying it was a "tough target", but he hoped it could be achieved.More news: Inside the world premiere of The Lion King
Attenborough had earlier told the hearing that he drew hope from an upsurge in environmental activism by a younger generation aware that they would bear the brunt of climate impacts as the crisis worsened in coming decades.
It said there has been little progress on many areas for cutting emissions, and the gap between what is being done and what needs to be done to meet existing targets to curb climate change is growing, the committee warned.
It's an intriguing comparison.
Painting a vivid picture for MPs of coral reefs turned "stark white" by warming waters, Sir David warned that the world faced a "serious collapse" caused by climate change over the next 20-30 years.
"These kind of problems are going to grow inexorably and we are going to have to decide what we do about it, that's going to happen".
Despite the climate issues the world faces, Attenborough remains hopeful.More news: Firefighters Tackling Blaze at Warner Bros.' UK Studios at Leavesden
Because not only is it pretty but it's been protecting our coastlines, preventing tidal waves and tropical storms from washing away our cities, regulating the carbon dioxide levels of the ocean to combat climate change and keeping our air and beaches clean.