Prince William's children have driven home for him how urgent it is to "fix the planet"

He said in a short film shared on his social media channels: "Now, more than ever, is the time to fix the planet.

"I sat under this oak tree five years ago, soon after we launched The Earthshot Prize. The planet, the only home we have, needed our help, as scientists made it clear that we had to make significant changes by 2030.

"Back then, a decade felt a long time. George was seven, Charlotte five and Louis two; the thought of them in 2030 felt a lifetime away.

"But today, as we stand halfway through this critical decade, 2030 feels very real.

"The Earthshot Prize was founded because this decade matters. 2030 is a threshold by which future generations will judge us; it is the point at which our actions, or lack of them, will have shaped forever the trajectory of our planet."

William praised the "urgent optimism" of the finalists, who he described as "heroes of our time".

He said: "It is impossible to hear these finalists' stories, to see the impact they are already having and not feel encouraged by their energy and momentum.

"For me, it is that urgent optimism that has been at the heart of this Prize from the beginning. And it feels unstoppable.

"The people behind these projects are heroes of our time, so let us back them. Because, if we do, we can make the world cleaner, safer and full of opportunity - not only for future generations, but for the lives we want to lead now."

Jason Knauf, CEO of the Earthshot Prize, believes the initiative is "more important than ever".

He said: "Earthshot was founded because we are in a decisive moment. it's a ten-year window of opportunity where our actions today will shape life on Earth for generations to come.

"The Earthshot Prize was also founded because Prince William believes that this decade can be a great human success story.

"That with urgency and optimism we can make these years count. Today as we stand at the half way mark of our mission, our work feels more important than ever.

"And we continue to be driven by the belief that the solutions already exist, we just need to identify, celebrate and back them. Today that's exactly what we're doing.

"The 15 finalists we are about to present alongside the amazing 60 before them are showing the world what's possible."

This year's ceremony will take place in Rio de Janeiro next month.