The Duke of Sussex was duped into speaking about his decision to quit the royal family by Russian hoaxers posing as activist Greta Thunberg.
During two phone calls recorded by the pranksters, Harry also claimed that US President Donald Trump has "blood on his hands", the Sun reported.
Speaking about Prime Minister Boris Johnson, the duke described him as a "good man" but as someone who is set in his ways.
The phone conversations, said to have been made by Vladimir Kuznetsov and Alexey Stolyarov – known as Vovan and Lexus – took place on New Year's Eve and January 22.
They tricked Harry into believing he was speaking to 17-year-old climate change activist Greta and her father.
Speaking about his decision to step down as a senior royal, the duke said: "Sometimes the right decision isn't always the easy one", the Sun reported.
"And this decision certainly wasn't the easy one but it was the right decision for our family, the right decision to be able to protect my son.
"And I think there's a hell of a lot of people around the world that can identify and respect us for putting our family first."
An extract from one of the recorded calls was published on YouTube along with an animated cartoon of Harry.
In the audio, a voice which is reportedly the duke's tells hoaxers that the world is being led by "some very sick people".
"The fossil fuel industry and certain presidents around the world are driving completely the wrong agenda," he said.
"I think the mere fact that Donald Trump is pushing the coal industry so big in America, he has blood on his hands.
"Because the effect that that has on the climate and the island nations far, far away – again out of sight, out of mind."
Harry said in the recording that he was "confident" that in the next five to 10 years "things will change" with regard to the climate agenda.
He adds: "But we can't wait five to 10 years, so I think if Donald Trump can become president of the United States of America, then anything's possible, right?"
According to the Sun, the duke told the prankster posing as Greta that the activist is "one of the few people" who could reach into Prime Minister Mr Johnson's "soul" and get him to believe in her cause.
"But you have to understand that, because he has been around for so long, like all of these other people, they are already set in their ways," he reportedly said.
Members of the royal family have been the target of hoax callers before.
In 1995 Canadian DJ Pierre Brassard, pretending to be Canadian Prime Minister Jean Chretien, was put through to the Queen.
The pair spoke for around 15 minutes and he even managed to elicit a promise that she would try to influence Quebec's referendum on proposals to break away from Canada.
In 2012, a nurse who was treating the Duchess of Cambridge while she was pregnant took her own life after being duped by hoaxers.
Jacintha Saldanha had been tricked by two Australian radio DJs who impersonated the Queen and the Prince of Wales into giving a condition update on Kate, who was suffering severe morning sickness at the private hospital.