Fierce bargaining at UN climate talks in Azerbaijan dragged into Saturday after a $250 billion a year offer from rich nations was flatly refused by developing countries hardest hit by Earth's rapid warming.

Negotiations at Cop29 in Baku, Azerbaijan were scheduled to finish on Friday evening but a final deal on climate finance remains elusive.

A key task of the UN gathering, which kicked off on Nov 11 in Baku, Azerbaijan, is to establish a 2025-35 climate finance commitment from developed nations to developing countries, which is officially known as the New Collective Quantified Goal.

COPs have been getting progressively longer; the excellent team at Carbon Brief extrapolated the trend line, which suggests COP29 will end in the small hours of Sunday morning. Even that may be optimistic.

The main goal of COP29 is to agree how much money richer developed countries will provide poorer developing ones to help them fight climate change.