With this week’s UN climate science report laying bare the staggering economic costs and losses already faced from climate change, an inevitable question arises: who should pay?

Within UN climate negotiations, “loss and damage” refers to the costs countries are incurring from climate-related impacts and disasters - costs that disproportionately hit the world’s poor and vulnerable who did least to cause global warming.

Drawing on more than 34,000 references from the latest scientific papers, the report released on Monday by the UN Intergovernmental Panel on Climate Change (IPCC) confirmed that economic sectors from agriculture and fishing to tourism were already being damaged.

Extreme heat has fuelled crop losses. Rising seas have turbo-charged cyclones that have razed homes and infrastructure, slashing economic growth.

And as the bills mount up, poorer countries are left with even less to spend on heath, education and infrastructure – compounding suffering.

“It’s an unending situation,” said Anjal Prakash, a lead IPCC author and research director at the Indian School of Business.

The report is likely to intensify a years-long political fight over funding to pay for climate-linked losses, ahead of the next UN climate summit, COP27, in Eygpt in November.

Vulnerable countries for years have sought funding to help them shoulder these costs. So far, it hasn’t arrived, and rich nations have resisted steps that could legally assign liability or lead to compensation.

The mention of “loss and damage” in the 2015 Paris Agreement came with the caveat that it “does not involve or provide a basis for any liability or compensation”.

Last November at the COP26 climate summit in Glasgow, poor countries called for a special “loss and damage” fund to be established, but the United States and other rich nations resisted. The delegates agreed to set up a UN body to help countries address loss and damage, and to continue discussions towards making “arrangements” for funding.

But there is no clarity on where the money would come from.

“We can’t just create more talk shops when people are dying,” said Harjeet Singh, senior adviser at Climate Action Network. He said COP27 needed to establish the funding facility that developing countries, including China, had called for at COP26.

Singh and other campaigners said the IPCC report – which has been approved by nearly 200 governments – could intensify pressure on the world’s most powerful nations.

“It will help us to say that science is clear, the impacts are clearer now. So you are accountable for this, and you have to pay for this,” said Nushrat Chowdhury, a policy advisor at NGO Christian Aid.

Accounting for costs

The report’s discussion of climate losses is bolstered by recent improvements in “attribution science”, which allows scientists to confirm when climate change caused or worsened a specific extreme weather event.

Still, putting a number on the resulting losses remains contentious. For example, can climate-linked losses from a weather event be separated from losses caused by poor disaster planning? Can costs be counted for losses outside our economic systems, such as when nature is degraded or a community burial site is destroyed?

“We are still debating that in the scientific community,” said another IPCC lead author Emily Boyd, a professor at Sweden’s Lund University.

As climate disaster costs mount and UN negotiations remain stuck, some are considering other options.

“Liability and compensation have other avenues to be taken forward, which are courts,” said Saleemul Huq, an adviser to the Climate Vulnerable Forum group of 55 countries.

Sophie Marjanac, lawyer at environmental law firm ClientEarth, said the IPCC report “will generally support litigation” to address climate change.

The legal avenue faces other obstacles, however.

Last year a federal appeals court rejected New York City’s attempt to use state law to hold five oil companies liable to help compensate harm caused by global warming. The court said the regulation of greenhouse gas emissions should instead be addressed under federal law and international treaties.

“Challenges in climate change litigation are related to the law, not to do with the science,” Marjanac said. “The science has been clear, very clear for years.”