Global temperature to rise by at least 4C in next 90 years.

Global average temperatures will rise by 4C by the end of the century if carbon dioxide emissions are not reduced, experts have warned.

According to researchers at the University of New South Wales' Centre of Excellence for Climate System, the average temperature could rise by more than 8C by 2200 if emissions are not curbed.

Published in the journal Nature, scientists say global climate is more sensitive to CO2 than previous estimates have suggested.

Rises in global average temperatures of this magnitude will have profound impacts on the world
Steven Sherwood

In their study, the team looks at the role of cloud formation and if it will have a positive or negative effect on climate change.

Their observations showed that when water vapour is taken in by the atmosphere through evaporation, it can rise to 15km to form clouds producing heavy rain, or it can rise just a few km and return to the surface without forming clouds.

When it only rises only a few km, cloud cover is reduced as the process pulls vapour from higher cloud forming regions. Current models, they say, do not account for this lower-level water vapour process enough.

If only higher water vapour is accounted for, models show more cloud forms and subsequently there is an increased reflection of sunlight. But this is not the case in real-world observations.

When adjusted for real observations, models produce cycles that take water vapour to a range of heights in the atmosphere, meaning fewer clouds are formed.

Current models do not accurately account for cloud formation on climate change, report says. Reuters

This means increased sunlight and heat entering the atmosphere and therefore increased sensitivity to CO2.

Explaining their findings, lead author 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 1.5C 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."

When water vapour processes are "correctly represented", the doubling of CO2 – which will happen in the next 50 years – will result in temperature increases of at least 4C by 2100.

Sherwood said: "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.

"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."