UN research shows that the pledges and promises made last year by 80 countries to reduce climate change emissions fall well short of what is needed to hold the global temperature rise to 2C and avoid the worst consequences of global warming.

The findings by 30 leading scientists suggest that if countries do everything they have promised, there will still be a 5bn tonne gap per year between their ambition and what the science says is needed. This gap, said the UN, is the equivalent of the emissions released by all the world’s vehicles in a year. Many countries have committed themselves to holding temperature rises to no more than 2C (3.6F) by 2080 but to achieve this global emissions must be reduced from 56bn tonnes annually today to 44bn tonnes by 2020.

If only the weakest pledges made last year in the Copenhagen accord are implemented, emissions could be lowered to 53bn tonnes a year by 2020, leaving a gap of 9bn tonnes.

In the best case, says the report, emissions could drop to 49bn tonnes, reducing the gap to 5bn. But if nothing is done, then the emissions gap would rise to 12bn tonnes by 2020 – roughly what all the world’s power stations emit.