By the end of this century world temperature will increase by at least 4°C if current CO2 emissions are not reduced.
The findings come from a study published in Nature, carried out by a group of researchers from the University of New South Wales’ Centre of Excellence for Climate System Science in Australia.
The world’s climate is more sensitive to CO2 (carbon dioxide) emissions than previous estimates, the scientists added.
The research team also solved a great unknown – what role cloud formation has on climate and whether it influences world temperatures.
Lead author, Prof Steven Sherwood said:
“Our research has shown climate models indicating a low temperature response to a doubling of carbon dioxide from preindustrial 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 1.5°C to 5°C. This new research takes away the lower end of climate sensitivity estimates, meaning that global average temperatures will increase by 3°C to 5°C with a doubling of carbon dioxide.”
By gathering and examining data from real world observations regarding the role of water vapor in cloud formation the scientists were able to make a narrower but much higher estimate of its impact.
The study authors found that when water vapor rises into the atmosphere through evaporation, the updraughts either rise to 15 km to form clouds that produce heavy rain, or just rise a few kilometers into the air and then return to the surface without forming rain clouds.
When water vapor rises just a few kilometers and then comes down again, cloud cover is much smaller – the updraughts pull more vapor from the higher cloud forming areas.
When only deep 15 km updraughts are present, water vapor is not pulled away from cloud forming regions.
World temperature predictions must be modeled on both types of updraughts
The authors found that climate models showing a low worldwide temperature response to CO2 do not include vapor that rises just a few kilometers. Rather, they simulate almost all updraughts as rising to 15 kilometers and forming clouds.
When just cloud-forming updraughts are present in the climate models, there are obviously more clouds and greater reflection of sunlight (and heat). Consequently, global climate predictions in these models underestimate sensitivity to atmospheric CO2.
According to real observations, however, this behavior is wrong. The researchers wrote “When the processes in climate models are corrected to match the observations in the real world, the models produce cycles that take water vapor to a wider range of heights in the atmosphere, causing fewer clouds to form as the climate warms.”
This raises the amount of light and heat that enters the atmosphere, which in turn increases the sensitivity of our climate to CO2 or any other disturbance.
When water vapor processes are represented correctly, the planet’s sensitivity to a doubling of CO2 would result in an increase in global temperature of 4°C or more. Experts say that CO2 levels will double within the next 50 years.
Prof. Sherwood said:
“Climate sceptics like to criticize 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.
“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.”
