There is a 50-50 chance of temperature rises reaching dangerous levels over the next century, climate scientists have warned.

Even with heavy cuts in greenhouse gas emissions of 3 per cent a year from 2015, the chance of preventing the temperature rise from exceeding 2C 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.

European leaders have made a commitment to limiting rises to 2C because anything above that is expected to damage people's lives and the environment. A 2C increase would in itself cause more heat waves and droughts, many of which could be worse than the 2003 heat wave, which killed thousands of people across Europe.

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.

Jason Lowe, of the Hadley Centre, will present findings showing that gas emissions, including carbon dioxide, should peak by 2015 and fall 3 per cent annually until 2050 if they are to be reduced to half of those in 1990.

The 50 per cent cut by 2050 is seen widely as the minimum necessary for the EU to have a reasonable expectation of limiting temperature rises to 2C. 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 per cent annually, the temperature rise will be 2.9C. If emissions peak in 2035 the average temperature will rise by 4C above pre-industrial levels. Failure to cut emissions at all could leave temperatures to rise by 7.1C by the end of the century.

Scientists fear that temperature rises above 2C would lead to wars over key resources, including water supplies, falls in crop yields in southern Europe and the spread of diseases such as malaria and dengue fever. Almost a third of animal and plant species could become extinct. Warm-water corals are among the species most at risk; animals that will struggle to survive include polar bears and emperor penguins.

Before leaving for Copenhagen, Dr Lowe said: “If global warming continues unabated then the risks of even greater warming are increased, making climate change more dangerous.”

Since 2000 global greenhouse gas emissions have risen between 2 per cent and 3 per cent each year, roughly in line with the rate of increase of the world's gross domestic product. The 0.5 per cent contraction of the global economy has led to greenhouse gas emissions falling by the same amount.

Vicky Pope, head of climate change advice at the Hadley Centre, said that a 2C rise could be delayed but it was extremely unlikely that it could be avoided.

“In order to stabilise at a 2C rise we have to make very drastic cuts,” she said. “But however drastic the emission cuts are, there is going to be a rise in temperatures.

“We are pretty much going to head towards 2C whatever we do. There are some impacts that are already happening and we are going to be living in a very different world.”

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