There is a 50-50 chance the Earth's temperature will rise to a level of disaster over the next century, according to research from British climate scientists.
Even with heavy cuts in greenhouse gas emissions of 3 percent a year from 2015, the chance of preventing the temperature rise from exceeding 2 degrees Celsius (3.8 degrees Fahrenheit) by 2050 is no more than half. And every decade's delay in reducing emissions will cause temperatures to go up by half a degree, say researchers.
European leaders have made a commitment to limit global temperature rises to 2 degrees Celsius because it is believed anything above that could do catastrophic damage to lives and the environment.
A 2-degree increase would in itself cause more heat waves and droughts, many of which could be worse than the 2003 European heat wave, which killed thousands of people.
The warning by researchers at the Met Office Hadley Centre, Exeter, will be made this week at a conference in Copenhagen, which is being held in preparation for a United Nations summit in the city in December, when world leaders will try to agree how to cut gas emissions enough to control climate change.
Dr. Jason Lowe, of the Hadley Centre, will present findings showing that gas emissions, including carbon dioxide, should peak by 2015 and fall 3 percent annually until 2050 if they are to be reduced to half of those in 1990.
The 50 percent cut by 2050 is seen widely as the minimum necessary for the EU to have a reasonable expectation of limiting temperature rises to 2 degrees Celsius. Legislation in Britain imposes a minimum cut in emissions of 80 per cent by 2050.
Dr. Lowe is expected to say that if emissions peak in 2015 but are reduced at a rate of only 1 percent annually, the temperature rise will be 2.9 degrees Celsius. If emissions peak in 2035 the average temperature will rise by 4 degrees Celsius above pre-industrial levels. Failure to cut emissions at all could leave temperatures to rise by 7.1 degrees Celsius by the end of the century.