The Prince of Wales has been awarded in the US for his environmental work.
The royal couple at a concert at Philadelphia's Academy of Music
He was awarded the Global Environmental Citizen Prize by Harvard Medical School's Center for Health and the Global Environment in New York.
Prince Charles, on a three-day tour in the US with his wife Camilla, received the prize from last year's winner, former Vice President Al Gore.
The prince said mankind was unlikely to stop damaging the planet until there was a change of outlook.
However, some environmental campaigners have criticised the prince for flying to the US to pick up the award and said he should have accepted it via video link.
Harvard Medical School's Center for Health and the Global Environment said Prince Charles was awarded the prize for "his outstanding work towards protecting the environment".
He told the audience the campaign had taken on greater urgency.
"Every passing year has seen further evidence emerge of the damage we are doing to this poor old planet, the only one we've got so far... that sustains life in such a miraculous and well-ordered way," the prince said.
Earlier, the royal couple visited New York's Harlem Children's Zone and saw several social service, health and educational projects.
A meeting with schoolchildren and their families to watch a maths carnival, basketball practice and rehearsal for Shakespeare's A Midsummer Night's Dream were also on the itinerary.
They arrived in New York on board a private electric train with academics and policy makers.
Charles and Camilla's decision to travel to city by train, rather than take an internal flight, is seen as an attempt to appear more environmentally friendly.
They arrived at Penn Station after leaving Philadelphia's 30th Street Station in three vintage carriages, powered by The Pennsylvania Railroad Business Car 120 locomotive.
It is the same one that once transported John F Kennedy to a football game, and later transported the body of his brother Robert Kennedy to Washington after he was assassinated.
On Saturday the royal couple were welcomed at a civic reception in Philadelphia by the governor of Pennsylvania, Ed Rendell, where 400 people gathered outside.
Charles and Camilla also saw the city's famous Liberty Bell, with its distinctive crack down the side.
They then attended a white-tie concert at Philadelphia's Academy of Music where the bill included rock star Rod Stewart.
The duchess wore a spectacular necklace - 36 rubies interlaced with diamonds - which Clarence House said had been presented to her while she was accompanying Charles on other recent overseas duties.
But they refused to confirm who gave her the generous gift.
Camilla teamed the rubies with a deep red velvet Robinson Valentine floor-length evening gown.
The prince and the duchess travelled to the US on a scheduled British Airways flight from Heathrow.