Global temperatures could rise 4 degrees by 2100
Global average temperatures could rise at least 4 degrees Celsius by 2100 and twice that by 2200 if carbon dioxide emissions are not reduced, according to a new study published in the journal Nature. So, Scientists found global climate is more sensitive to carbon dioxide than most previous estimates.
The research also appears to solve one of the great unknowns of climate sensitivity: the role of cloud formation on global warming. “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,” said lead author from the University of New South Wales’ Center of Excellence for Climate System Science Steven Sherwood.
“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.”
The key to this new estimate is real world observations of water vapor’s role in cloud formation. When water vapor is taken up by the atmosphere via evaporation, updraughts can rise up to 15 km to form clouds that then result in heavy rain, or just a few kilometers before they return to the surface again, never having formed rain clouds. These less ambitious updraughts reduce total cloud cover because they draw more vapor away from the higher-up regions where clouds are formed.
Together, the scientists realized that climate models indicating a limited global temperature response to carbon dioxide fail to include sufficient levels of this lower-level process, instead simulating nearly all updraughts as rising to 15 km where they go on to form clouds. This increase in clouds means an increase reflection of sunlight, causing the climate to become less sensitive to atmospheric carbon dioxide.
So, Sherwood showed his worry. “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.”