New Models Reveal Global Temperatures May Rise Four Degrees by 2100

Global temperatures are continuing to rise. Yet exactly how fast and how far will they go? Scientists have found that global average temperatures will rise at least 4 degrees Celsius by 2100 and potentially more than 8 degrees by 2200 if carbon dioxide emissions aren't reduced. The findings show the importance of reducing these emissions before it's too late.

"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 Steven Sherwood, one of the researchers, in a news release. "When 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 degrees C to 5 degrees C. This new research takes away the lower end of climate sensitivity estimates, meaning that global average temperatures will increase by 3 degrees C to 5 degrees C with a doubling of carbon dioxide."

So why does this higher estimate exist? It's due to the real world observations around the role of water vapor in cloud formation. Water vapor is taken up by the atmosphere through evaporation. The updraughts can either rise to 15 km to form clouds that produce heavy rains or just rise a few kilometers before returning to the surface without forming rain clouds. When updraughts rise only a few kilometers, they reduce total cloud cover because they pull more vapor away from higher cloud forming regions. Yet water vapor is not pulled away from low forming regions.

So what does this have to do with temperature? The scientists found climate models that showed a low global temperature response to carbon dioxide do not include enough of this lower-level water vapor process. Instead, they simulate nearly all updraughts as rising 15 km and forming clouds.

"Climate skeptics 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," said Sherwood in a news release. "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."