Rich countries have failed to meet a $100 billion promise to help developing nations tackle climate change — but there is hope that they could meet the target by 2023.
The announcement sets the stage for tricky negotiations at the Cop26 summit, at which leaders will be urged to open their wallets to support the global south.
Cop26 president Alok Sharma acknowledged "deep frustration" from poorer countries that the money had not been delivered, more than a decade after it was first promised in 2009.
Many developing nations are particularly vulnerable to climate-related disasters, such as floods and droughts, which will become far more frequent if global warming is not kept in check.
Leaders of developing countries say they need the money to help them grow their economies sustainably, without relying on fossil fuels.
But a report commissioned by Mr Sharma said the promised $100bn had not been raised by the 2020 deadline.
“Even though final figures for 2020 are not available yet, it is becoming clear that developed countries will not have mobilised US$100 billion jointly,” it said.
Total funds rose to $79.6bn by 2019, with most of the money coming from taxpayers rather than the private sector. The report welcomed a "significant effort by developed countries" but said there was still a shortfall.
"Understandably, this has been a source of deep frustration for developing countries," said Mr Sharma. "We can and must do more to get finance flowing to developing nations.
"Crucially, we must increase the sums available for climate adaptation, and we must also urgently improve access to finance. So our work continues."
Jochen Flasbarth, a state secretary in Germany's Environment Ministry, said developing countries were "rightfully disappointed" by the lack of funds.
The ministers set out what they called a Delivery Plan to get the money together by 2023, mainly relying on increased spending from governments.
"It is my strong hope that with this plan, we can show the international community that developed countries remain committed to deliver on their promises," Mr Flasbarth said.
The wealthy countries expected to stump up the money are mainly in Europe and North America, but also include Australia, Japan and New Zealand.
Monday's report was spearheaded by ministers from Germany and Canada, and did not point the finger at specific countries for failing to meet the target.
But experts and aid groups have criticised the US for donating too little money, given the size of its economy, population and carbon footprint.
President Joe Biden plans to double Washington’s contribution during his first term and the report said there were encouraging signs in a number of countries.
“The outlook to 2025 shows a positive trend,” it said, with rich countries “making significant progress towards the $100 billion goal in 2022”.
As a result, the study authors “express confidence that it would be met in 2023”. Mr Sharma said there could be $117bn by 2025.
Teresa Anderson, a climate lobbyist at the charity ActionAid, said the $100bn was a bare minimum needed to build trust in global talks.
"World leaders must recognise and address the glaring gap between the current 100 billion-a-year target and the trillions needed to tackle the scale and urgency of the crisis," she said.
The funding promise agreed in Copenhagen more than a decade ago runs until 2025, when the UN expects a more ambitious target to be adopted.
This will be one of the topics discussed at Cop26, where Mr Sharma hopes to prepare the ground for a new target to be set.
Britain plans to spend £11.6bn ($16.0bn) on climate finance by 2026. The EU is urging other countries to find more money by cutting fossil fuel subsidies.
Private financing has proved disappointing, according to Monday’s report, which said it remained “more or less flat” from 2017 to 2019. Mr Biden’s administration has said it will try to raise more money from investors.
China and India, two of the world’s biggest polluters, are not considered developed countries and therefore not expected to contribute.
However, they will be key players in negotiations on fossil fuels, especially the future of coal power.
The UK wants coal to be “consigned to history” at Cop26, but India has evaded calls for a global agreement to phase it out.
Speaking to schoolchildren on Monday, UK Prime Minister Boris Johnson expressed concern on Monday that the Glasgow summit "might go wrong".
"It's very, very far from clear that we'll get the progress that we need," he said. "We might not get the agreements that we need and it's touch and go."