The Duke said: "This last week, led by Greta, the world's children are striking.
"There is an emergency, it's a race against time and one in which we are losing, and everyone knows it.
"There is no excuse for not knowing, that I think the most troubling part of it is - I don't believe there is anybody in this world that can deny science, undeniable science and facts.
"Science and facts that have been around the last 30, nearly 40 years, and it's only getting stronger and stronger.
"Genuinely I don't understand how anyone in this world, whoever we are, you, us, children, leaders, whoever it is, no-one can deny science, otherwise we live in a very, very troubling world."
On a more personal note, Harry then opened up about how Botswana had offered him refuge after the death of his mother.
“Fifteen years I’ve been coming here, it’s a sense of escapism, a real sense of purpose … I have some of my closest friends here over the years," he said.
"I came here in 1997, 1998, straight after my mum died, so it was a nice place to get away from it all.
"But now I feel deeply connected to this place and to Africa."
Harry and Meghan's use of private jets has led to recent criticism of the couple, and accusations of hypocrisy as they speak out on climate change and environmental issues.
The Duke and Duchess of Sussex will continue on their royal tour of Africa until October 2.
