Prince William said: "2025 marks the midway point of the Earthshot decade and each year we've witnessed the remarkable power of human ingenuity in addressing our planet's most pressing challenges."
"It is an honour to profile the people making our world a better place for us and for our children," he added.
A video announcing the plans featured the prince and several Earthshot supporters including David Beckham, Cate Blanchett, Hannah Waddingham and former Brazilian footballer, Cafu.
Fifteen projects will be shortlisted for a chance of winning the prizes.
The judging panel has received 232 nominations from projects based in South America – more than double the number received from the region last year.
Christiana Figueres, chair of the board of Earthshot trustees, has led a number of negotiations on international climate accords during a long career pushing for global climate solutions.
As a Costa Rican, Ms Figueres said it was a significant moment to see Brazil host the prize.
"It's very exciting, certainly for me as a Latin American….Brazil is at the heart of the challenge Earthshot faces," she told me.
"To have the prize come in just before COP brings attention to Earthshot. It is win-win for both COP and Earthshot."
This year's Earthshot is being viewed as the curtain raiser to COP which is due to begin a few days later in Belém, the gateway to the Amazon.
It comes against the backdrop of Donald Trump's recent return to the White House in the US.
Trump is a known climate sceptic who has been vocal in his criticism of global climate action.
"That doesn't help but it doesn't stop the progress either," Ms Figueres said.
"He can't stop the advance of green technologies, he can't stop the public demand for cleaner air and a more sustainable world. None of that can stop because of political ignorance."
Ahead of COP, there has been criticism of Brazil from conservationists for cutting down tens of thousands of acres of protected Amazon rainforest to build a new four-lane highway in preparation for the climate summit.
