An apocalyptic scenario, if radical action is not taken to cut carbon emissions soon, has been painted by the normally cautious Met Office. A study by the UK Met Office’s Hadley Centre says that action must be taken within just two years if damaging climate change is to be avoided.

The study shows that cutting global emissions by 3% a year from 2010 offers the only possible hope of avoiding a global temperature rise of more than 2C – widely recognised as the threshold beyond which the worst impacts of sea level rise and drought become a significant risk.

It raises the prospect of far-reaching changes, including a rapid spread in wave and tide power, improvements in public transport, big shifts to cycling and walking and changes in diet. It would also lead to huge pressure for the UK to abandon plans for a third runway at Heathrow, a new ‘Heathrow-on-Sea’ in the Thames Estuary and new coal-fired power stations.

The Hadley Centre advises the UK government, the United Nations and other governments and businesses and will spur calls for urgent action at the big UN meetings in Poznan, Poland, in December and in Copenhagen at the end of next year, when a replacement for the Kyoto protocol is due to be agreed.

At 2C, scientists have warned that at least one fifth of species are at risk of extinction and 1 to 2 billion people could suffer increased water stress; above 2C plants and soil significantly reduce the amount of carbon they absorb; and above 4C experts warn there is a danger of passing a “tipping point” at which methane release from permafrost and the collapse of big ice sheets accelerate the problems.