Prince Charles warned last night that mankind has eight years or less to save the planet from a climate-created disaster.

The heir to the throne told 150 business leaders in Rio de Janeiro, Brazil, that "the best projections tell us that we have less than 100 months to alter our behaviour before we risk catastrophic climate change and the unimaginable horrors that this would bring".

He added: "Any difficulties which the world faces today will be nothing compared to the full effects global warming will have on the worldwide economy. It will result in vast movements of people escaping either flooding or droughts, in uncertain production of foods and lack of water and, of course, increasing social instability and potential conflict.

"It will affect the well-being of every man, woman and child on our planet." The prince's warning coincided with scientists' claims, at a Copenhagen conference, that the world is facing an increasing risk of "irreversible" changes to our climate as global warming speeds beyond the worst predictions.

Experts said temperatures, sea levels, ice sheets, oceans and extreme weather were already moving "beyond the patterns of natural variability within which our society has developed and thrived".

The situation even worse than worst-case scenarios predicted by the Intergovernmental Panel on Climate Change, which issued warnings in 2007 of a future beset by flooding, drought, storms and mass extinction of species, said the scientists.