World leaders descended on the United Nations annual climate summit in Brazil on Thursday.

Addressing the delegations, Brazilian President Luiz Inacio Lula da Silva said the world's eyes were on Belem, the host city in the heart of the Amazon rainforest.

"More than 30 years after the Earth Summit in Rio de Janeiro, the climate convention returns to the country where it was born. Today the eyes of the world turn to Belem with immense anticipation," he said.

Antonio Guterres, united Nations Secretary-General, also addressed the delegations Thursday.

He warned of "unliveable conditions" should global temperatures continue to rise.

"Every fraction of a degree means more hunger, displacement, and loss, especially for those least responsible," he said.

Britain's Prince William was also at the summit after hosting the Earthshot Prize in Rio de Janeiro earlier this week.

"All of us here today understand that we are edging dangerously close to the Earth's critical tipping points, thresholds beyond which the natural systems we depend on may begin to unravel," he said.

"These are not distant threats; they are fast approaching and will affect every one of us no matter where we live," the prince added.

As the summit progresses, Lula is expected to unveil a flagship multibillion-dollar international fund to offer compensation to countries who help preserve forested areas.

Organizers are hoping this COP30 will yield action to advance the many unmet promises laid out at previous such meetings.