It's time for the global community to "grow up" and deal with the climate change crisis, British Prime Minister Boris Johnson told United Nations representatives, urging nations to "listen to the warnings of the scientists" in remarks at odds with some of his past statements.

Speaking in New York on Wednesday, Johnson said countries need to take responsibility for "the destruction we are inflicting, not just upon our planet, but ourselves."

"We still cling with parts of our minds to the infantile belief that the world was made for our gratification and pleasure," he told delegates at the 76th session of the U.N. General Assembly. "And we combine this narcissism with an assumption of our own immortality."

"We believe that someone else will clear up the mess, because that is what someone else has always done," Johnson said.

He said that an upcoming U.N. climate change conference in Scotland in November would be a "turning point for humanity."

Along with climate change, Johnson pointed to COVID-19 as another "example of gloomy scientists being proved right."

But trumpeting the scientific consensus on climate change is a somewhat recent position for Johnson.

Since becoming prime minister two years ago, he has sounded a largely mainstream message, promising in April, for instance, to "build back greener" after the coronavirus pandemic. But in years previous, Johnson has supported conspiracy theorists who deny a link between human activity and climate change.

Asked recently to defend past tweets by his newly appointed trade secretary, who had called climate change scientists "doom-mongers" and "fanatics," Johnson acknowledged that some of his own past articles "from 20 years ago" were not "entirely supportive of the current struggle."

"Facts change," he said, according to The Guardian, "and people change their minds."