Global temperatures set 'to increase'
Global temperatures are set to increase by up to five degrees centigrade by 2100, according to a study suggesting that climate is more sensitive to greenhouse gas emissions than was previously thought.
By 2200, the world could be more than 8C warmer than it was in pre-industrial times if carbon dioxide emissions are not reduced, say the researchers.
The study corrected what were claimed to be earlier errors in calculating the effect of clouds on global warming.
Lead scientist Professor Steven Sherwood, from the University of New South Wales in Australia, said: "Our research has shown climate models indicating a low temperature response to a doubling of carbon dioxide from pre-industrial times are not reproducing the correct processes that lead to cloud formation.
"When the processes are correct in the climate models the level of climate sensitivity is far higher. Previously, estimates of the sensitivity of global temperature to a doubling of carbon dioxide ranged from 1.5C to 5C.
"This new research takes away the lower end of climate sensitivity estimates, meaning that global average temperatures will increase by 3C to 5C with a doubling of carbon dioxide."
The new findings are reported in the journal Nature.
Climate models had failed to take sufficient account of low-level air currents pulling water vapour from higher cloud-forming regions and reducing the amount of cloud cover, said Prof Sherwood's team.
When they were adjusted to match observations in the real world, the computer simulations produced cycles that took water vapour to a wider range of heights in the atmosphere and caused fewer clouds to form.
This, in turn, increased the amount of sunlight and heat entering the atmosphere.
"Climate sceptics like to criticise climate models for getting things wrong, and we are the first to admit they are not perfect, but what we are finding is that the mistakes are being made by those models which predict less warming, not those that predict more," said Prof Sherwood.
"Rises in global average temperatures of this magnitude will have profound impacts on the world and the economies of many countries if we don't urgently start to curb our emissions."