Prince Harry has said the science on the climate crisis is undeniable as, led by Greta Thunberg, the “world’s children are striking” to force action.

The Duke of Sussex is in Botswana helping to create a new forest habitat after decades of deforestation because of locals gathering firewood and through elephant activity.

Speaking on the banks of the Chobe River, he referred to the speech by the UN secretary general, António Guterres, at the UN general assembly in which he warned that the world had seen unprecedented temperatures.

“This week, led by Greta, the world’s children are striking. There’s an emergency. It’s a race against time and one which we are losing. Everyone know it. There’s no excuse for not knowing that,” he said.

“And the most troubling part of that is I don’t believe there is anybody in this world who 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 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.”

It takes several men, including Harry, to plant a 10-metre baobab tree. Photograph: Dominic Lipinski/Getty Images

Prince Harry, whose use of private jets has led to criticism and accusations of environmental hypocrisy, was working with a conservation organisation helping locals to create a nature and cultural park for the community.

He shared the strain with a group of men to get a 10 metre (32ft) baobab tree into the ground, then joined young schoolchildren planting mahogany saplings.

He was accompanied by Dr Mike Chase, conservationist and founder of Elephants Without Borders, which will manage the new reserve with the aim of creating a thriving riverbank forest. Harry also met youth leaders from his Sentebale charity, which supports young people affected by HIV, at a health centre in Kasane.

On a highly personal note, Harry spoke of how Botswana had offered him a place to escape following the death of his mother, Diana, Princess of Wales.

“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.

“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,” he said.