A UN report has revealed that wealthy donor countries are more than $20bn short of their 2020 target to help poorer nations combat climate change, as the host of next month’s international climate summit warned that funding will be a contentious issue. Rich nations delivered about $55bn in climate-related public aid in 2016, or more than $70bn if private capital is included, according to the report seen by the Financial Times.

But both figures fall short of the $100bn per year that rich countries have been promising poorer countries for nearly a decade. Michal Kurtyka, the Polish minister presiding over the summit in the city of Katowice, said funding will be one of the main sticking points in the negotiations that begin on December 3. “There is a very big debate around the issue of mobilisation of funding,” he said.

The promise of $100bn in annual climate funding by 2020 was a vital element that convinced developing countries to back the Paris climate agreement in 2015, but it has become a major source of disagreement. The Paris accord committed nations to limit global warming to well below 2C, but left it to individual countries to set their own targets on how to accomplish this. This year’s talks, the most significant since Paris, will face an uphill battle on issues such as deciding the rule book agreed in France. There are also growing fears that the threat of trade wars and nationalism may damage the co-operation that underpins climate talks.