London, August 7 : A scientist has suggested that the world should be prepared to face an alarming increase of 4 degree Celsius in global temperatures.
A report in The Guardian said that this was suggested by agriculture and coastal erosion Professor Bob Watson, who is one of the UK government's chief scientific advisers.
In policy areas such as flood protection, UK should plan for the effects of a 4C global average rise on pre-industrial levels, said Watson.
Globally, a 4C temperature rise would have a catastrophic impact.
According to the government's 2006 Stern review on the economics of climate change, between 7 million and 300 million more people would be affected by coastal flooding each year.
Also, there would be a 30-50% reduction in water availability in Southern Africa and the Mediterranean, agricultural yields would decline 15 to 35% in Africa and 20 to 50% of animal and plant species would face extinction.
In the UK, the most significant impact would be rising sea levels and inland flooding.
Climate modellers also predict there would be an increase in heavy rainfall events in winter and drier summers.
The EU (European Union) is committed to limiting emissions globally so that temperatures do not rise more than 2C.
"There is no doubt that we should aim to limit changes in the global mean surface temperature to 2C above pre-industrial," said Watson.
"But given this is an ambitious target, and we don't know in detail how to limit greenhouse gas emissions to realise a 2 degree target, we should be prepared to adapt to 4C," he added.
Watson's plea to prepare for the worst was backed up by the government's former chief scientific adviser, Sir David King.
According to King, even with a comprehensive global deal to keep carbon dioxide levels in the atmosphere at below 450 parts per million, there is a 50% probability that temperatures would exceed 2C and a 20% probability they would exceed 3.5C.
"So even if we get the best possible global agreement to reduce greenhouse gasses on any rational basis you should be preparing for a 20% risk so I think Bob Watson is quite right to put up the figure of 4 degrees," he said.
"At 4 degrees we are basically into a different climate regime," said Professor Neil Adger, an expert on adaptation to climate change at the Tyndall Centre for Climate Change Research in Norwich.
"There is no science on how we are going to adapt to 4 degrees warming. It is actually pretty alarming," he added.