The Duke of Cambridge has issued a rallying cry to the next generation to keep on "demanding change" as innovative green projects from across the globe were awarded $A1.9 million by his Earthshot Prize.
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William called on young people not to "give up hope" during the event.
At the end of the event, televised by the BBC, William, who was joined by his wife Kate, took to the stage to tell the audience: "I want to say something to the young watching tonight".
"For too long, we haven't done enough to protect the planet for your future, the Earthshot is for you," he said.
"In the next 10 years, we are going to act.
"We are going to find the solutions to repair our planet.
"Please keep learning, keep demanding change, and don't give up hope.
"We will rise to these challenges."
Harry Potter star Emma Watson, wearing a wedding dress made of 10 recycled dresses, and Dame Emma Thompson were among those who trod the ceremony's green carpet.
Kate arrived wearing an Alexander McQueen dress made for her in 2011, while her husband wore a dark green velvet blazer and a polo neck.
No stars flew to London for the event and guests were asked by organisers to "consider the environment when choosing their outfit" for the awards inspired by the Apollo moon landings, nicknamed Moonshot, which helped advance mankind's technological achievements.
Among the winners were projects restoring coral reefs, redistributing unwanted food to the disadvantage, and a project battling the issues contributing to air pollution in India.
Kate presented the winning award in the protect and restore nature category to the government of Costa Rica, which has pioneered a project paying local citizens to restore natural ecosystems.
"Nature is vital to us all, she said.
"A thriving natural world, regulates our planet, nurtures our physical and mental health and helps feed our families.
"But for too long, we've neglected our wild spaces and now we're facing a number of tipping points.
"If we don't act now, we will permanently destabilise our planet and we will rob our children of the future they deserve."
Liverpool FC soccer star Mo Salah presented the first Earthshot Prize in the revive our oceans category, to the Coral Vita project which grows coral on land to replant in oceans, giving new life to dying ecosystems.
Watson awarded the fix our climate prize to AEM Electrolyser technology which turns renewable electricity into emission-free hydrogen gas.
The Harry Potter star said: "There have been many other times in history where it's been said something couldn't be done, and then people believed in a better world and made it so.
"(This) time is no different, I know that we can."
The event was launched by the band Coldplay, who pre-recorded their performance, which was powered by 60 people pedalling bicycles, and Ed Sheeran also took to the stage to entertain the audience.
Australian Associated Press
