Rich countries will need to boost the $100bn (€75.9bn) in financial assistance given to the developing world each year by 50 to 100 per cent if they want a global deal to curb climate change, the United Nations’ top development official has told the Financial Times.

“If donors are not willing to think in these orders of magnitude, I am pessimistic,” said Kemal Dervis, head of the UN Development Programme, adding that the extra support was needed to make a deal “fair and workable”.