From the BBC:
"It is very unusual indeed to see such a dramatic shift in opinion in such a short period," Populus managing director Michael Simmonds told BBC News.
"The British public are sceptical about man's contribution to climate change - and becoming more so," he added.
"More people are now doubters than firm believers."
The Department for Environment, Food and Rural Affairs' (Defra) chief scientific adviser, Professor Bob Watson, called the findings "very disappointing".
"The fact that there has been a very significant drop in the number of people that believe that we humans are changing the Earth's climate is serious," he told BBC News.
"Action is urgently needed," Professor Watson warned.
"We need the public to understand that climate change is serious so they will change their habits and help us move towards a low carbon economy."