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Allowing the window of opportunity to close would represent a moral and political failure without precedent in human history

Nations must agree an action plan to curb climate change or face an "unprecedented reversal" in human development, a UN assessment warns.

The UN Human Development Report said the poorest nations risked a downward spiral of malnutrition, water scarcity and ecological damage.

While rich nations were able to afford to "climate-proof" their economies and population, poor nations were woefully under-funded.

According to the report, international funding for adaptation in developing nations to date amounted to $26m (£13m), roughly the same amount as the UK spends on its flood defences in a week.

The UN Development Programme (UNDP) report coincides with next week's key UN climate negotiations in Indonesia.

"It is the poor, a constituency with no responsibility for the ecological debt we are running up, who face the most immediate and severe human costs."