But he is no longer attending the event, as he and his family continue to observe a period of mourning for his late grandmother.
In a video - recorded on Tuesday at the Windsor Estate and broadcast on Wednesday - the prince said he believed the Queen would have “been delighted to hear about” the summit.
Earthshot Prize Awards Ceremony 2021 - In pictures
In a virtual message to those attending the event, William said: “Though it is the saddest of circumstances that means I cannot join you in person today, I am pleased to be able to join you in video form as you gather in New York for the Earthshot Prize innovation summit.”
He added: “During this time of grief, I take great comfort in your continued enthusiasm, optimism and commitment to the Earthshot Prize and what we are trying to achieve.
“Protecting the environment was a cause close to my grandmother’s heart. And I know she would have been delighted to hear about this event and the support you’re all giving our Earthshot finalists, the next generation of environmental pioneers.”
The royal family is continuing its period of mourning for the Queen, to be observed until seven days after the funeral.
Members of the royal family are not expected to carry out official engagements, and flags at royal residences will remain at half-mast until 8am on Tuesday – after the final day of royal mourning.
The Earthshot Prize was founded by William and his Royal Foundation in 2020, and in July this year the project became an independent charity, with the prince as its president.
The second Earthshot Prize awards ceremony is set to be held in Boston in December, after the inaugural event at London’s Alexandra Palace last year.