"We'll look back on all of this in 10 or 15 years and realise how foolish it was," Dr Gray said.
"The human impact on the atmosphere is simply too small to have a major effect on global temperatures," Dr Gray said.
He said his beliefs had made him an outsider in popular science.
"It bothers me that my fellow scientists are not speaking out against something they know is wrong," he said. "But they also know that they'd never get any grants if they spoke out. I don't care about grants."