Delegates from around the world will converge in the Amazon rainforest next week for the 30th annual climate change conference at a critical time for the planet, as the UN warned efforts to limit catastrophic global warming were falling short.

"We want to see if it's possible to launch a new phase of implementation for the COP, because here's the thing: enough talking, now we have to implement what we've already discussed," Lula said ahead of a meeting of around 50 heads of state in the Amazon city of Belem Thursday and Friday.

"We have already had several COPs, many decisions were made, many decisions were not implemented," added the 80-year-old leftist leader.

"We don't want the COP to continue being a fair of ideological and climate products...we want it to be very serious and for the things we decide to be implemented."

COP30, which begins next week after the meeting of heads of state, is being held in the Amazon for the first time, with some 50,000 people expected in Belem.

This has caused chaos around accommodation in a city not used to such a large number of visitors, with soaring prices prompting concerns that many from poorer nations are being excluded.

"When we decided to hold COP here...we already knew the conditions of the city. And we decided to do it here because we didn't want comforts, we wanted challenges. And we wanted the world to come and see the Amazon," said Lula.

He said the friendliness and local cuisine would make all visitors feel at home and that they would "leave a little fatter because they will eat well."

A report by the UN Environment Programme (UNEP) released Tuesday said the world was set to blow past a maximum global warming target of 1.5C in a matter of years.

The latest assessment finds that, even if all current pledges to curb emissions are fully implemented, the world is still on track for up to 2.5C of warming by 2100 -- a level that threatens the survival of nations most vulnerable to rising seas and extreme weather.