Video report by ITV News Royals Editor Chris Ship
Prince Harry stressed "no one can deny science" as the "world's children are striking" for action on climate change.
The Duke of Sussex is in Botswana helping to create a nature and cultural park for the community as art of his royal tour with Meghan and baby son Archie, both in South Africa.
In a brief interview at a new forest habitat on the banks of Botswana’s Chobe River, he referred to UN Secretary General Antonio Guterres' speech at the UN General Assembly, in which he warned the world has seen unprecedented temperatures.
“I don’t think there’s anyone that’s not involved in conservation somehow or shouldn’t be involved in conservation somehow,” he said.
“This last week, led by Greta Thunberg, the world’s children are striking. It’s a race against time and one which we are losing – everyone knows it, there’s no excuse for not knowing that.
“And I think the most troubling part of it is that 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 for the last 30, maybe 40, years and it’s only getting stronger and stronger.
“I genuinely 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.”
Prince Harry is back in Botswana more than 20 years after his first visit, which was months after his mother Diana, Princess of Wales died.
He spoke about how Botswana offered him a place to escape to following her death.
He said: "15 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.
"I came here in 1997 or 1998 straight after my mum died, so it was a nice place to get away from it all.
"I feel deeply connected to this place and to Africa."
The Duke of Sussex shared the strain with a group of men to get a 10-metre tree into the ground as he took part in the ultimate planting ceremony.
Harry clearly enjoyed the challenge of helping to create a new forest habitat.
After decades of deforestation from locals gathering firewood and elephant activity, a conservation organisation working with locals is trying to create a nature and cultural park for the community.
The duke got stuck in trying to plant the tree and worked with a group of men to push it upright before packing it with soil.
When he saw the huge mound of earth that needed to go into the hole, he smiled and joked: “How long do we have?”
Harry later joined school children planting mahogany trees, crouching down with one young child to help him pack the sandy soil around the tiny sapling and at the end he high-fived the youngster to celebrate.
When the duke first arrived he was hugged by his friend Dr Mike Chase, conservationist and founder of Elephant Without Borders, which is working with a local organisation to develop the site into a nature and cultural reserve.
The land was privately owned but has been pledged to the local community and Dr Chase’s organisation will manage it with the aim of creating a thriving riverbank forest.
ITV News Royal Editor Chris Ship says Harry has also spoken about why Botswana means so much to him.
He said it was where he came in the months following his mother's death.
Harry is on a solo leg of the royal tour to southern Africa. He will spend six days away from wife, Meghan and son Archie, who will stay in Cape Town.