The world has less than 15 years to take urgent action against global warming through the use of new technology if it is to prevent a climate catastrophe, the United Nations warns in the as yet unpublished third part of its World Climate Report.

If carbon emissions are not substantially reduced by 2020, the report warns, global warming will set in motion irreversible natural processes such as the melting of the ice shields in Greenland and the over-acidification of the oceans.