PARIS, France -- Insufficient investment in developing countries is putting efforts to reduce global warming at risk, a UN economics expert group said Wednesday, calling for COP28 to push for "radical change".

The UN's high level expert group on climate finance last year said developing nations (excluding China) need to spend some $2.4 trillion a year on clean energy and climate resilience by 2030 -- four times current levels.

In an updated analysis, released just before the start of crunch UN climate talks in Dubai, the authors warned that climate investment in emerging economies "has stalled" and that near-term action was critical.

"Why are we off track on emissions? Because we have not invested nearly enough in what we have to do to bring them down," said co-author Nicholas Stern. "We are in a hurry."

The central focus of the November 30 to December 12 COP28 talks will be a damning stocktaking of the world's limited progress on cutting greenhouse gas emissions.

The report said a failure to provide sufficient funding would "fail on Paris", referring to the landmark 2015 agreement to limit global warming to well below two degrees Celsius from preindustrial levels and preferably a safer 1.5C.

"The consequences would be devastating, particularly for the poorest people," it said.

Many developing nations least to blame for the greenhouse gases that stoke global warming are among the most exposed to the costly and destructive effects of extreme weather and rising seas.

But they are also some of the world's fastest-growing economies with surging demand that experts say could be best met by pivoting to clean energy -- if they can shrug off debt burdens and access financing.

The report said around $1.4 trillion of the $2.4 trillion needed would be domestic spending, adding international private finance needs to be increased by more than 15 times and funding from the multilateral development banks to triple.

"This is radical change," said Stern, who authored a landmark 2006 report on the economic impact of global warming.

- 'Huge' gap -

The authors stressed that the world needs to act fast.

"The more we wait, the more expensive it becomes," economist Vera Songwe, another of the report's co-authors told reporters, warning that the estimated investment needs would likely need to be revised upwards by 2025 if action is slow.

Finance has long been at the heart of international climate negotiations, with talks in recent years tainted by the failure of richer countries to make good on their 2009 promise to provide $100 billion a year in climate finance for resilience and clean energy by 2020.

That target looks likely to have been met last year, monitors have said, although needs continue to grow as climate impacts surge.

Developing countries have spearheaded a high profile campaign to refocus the World Bank and International Monetary Fund on climate priorities.

Experts have also suggested a range of taxes on high-emitting sectors to raise money -- particularly the shipping and airline industries -- as well as moves to redirect subsidies away from polluting activities and towards the green transition.

Songwe praised COP host United Arab Emirates for pledging $4.5 billion in September to accelerate Africa's switch to clean energy and said she would be looking for similar vows at the Dubai meeting.

"We know what is needed, but the gap between what is needed and what is being put in place today is still quite huge," she said.