Any more warnings that time is running out to stop global warming and Hollywood will have the script for a sequel to Groundhog Day. Tuesday’s report on climate change by the United Nations Development Programme sounds the latest alarm call. After the shortcomings of Kyoto, it declares, the world has one final chance to avert a disaster.

Like many blockbusters, the report’s conclusions are eye-catching. The cost of inaction will be higher than the spending needed to cut carbon emissions. A rise in temperature of 3-4 degrees Celsius could trigger catastrophe, depriving 1.8bn people of plentiful water supplies and displacing hundreds of millions more. Killer diseases could rampage through poor countries and species could become extinct. To avoid that, the report says, emissions must be cut by half. It puts the cost at 1.6 per cent of annual global output.