Britain should prepare for its climate to rise by 4C

Britain should prepare for its climate to rise by up to 4C, one of the Government's chief scientific advisers has said.

The UK and EU believe global warming must be limited to no more than a 2C temperature rise above pre-industrial times to avoid dangerous climate change.

But Professor Bob Watson, the chief scientific adviser to the Department for the Environment, Food and Rural Affairs, told the Guardian the country should plan for the effects of a 4C global average rise.

It would impact on policy areas such as agriculture, coastal erosion and flood protection.

Prof Watson told the newspaper: "There is no doubt that we should aim to limit changes in the global mean surface temperature to 2C above pre-industrial.

"But given this is an ambitious target, and we don't know in detail how to limit greenhouse gas emissions to realise a 2C target, we should be prepared to adapt to 4C."

The Government's 2006 Stern Review on the economics of climate change warns a 4C rise would leave global food production "seriously affected". It would also put hundreds of millions of people in small islands and coastal cities such as London and New York at risk of flooding because of rising sea levels.

To emphasise the impact of a 4C rise, the report states that we are now only around 5C warmer than in the last ice age.

Prof Watson's comments were echoed by the Government's former chief scientific adviser, Sir David King.

He said that even with a comprehensive global deal to keep carbon dioxide levels in the atmosphere at below 450 parts per million there is a 50% likelihood that temperatures would exceed 2C and a 20% probability they would exceed 3.5C.