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Our future: hotter than expected

03 January, 2014

Global average temperatures will rise at least 4°C by 2100 and potentially more than 8°C by 2200 if carbon dioxide emissions are not reduced, according to new research published in Nature that shows our climate is more sensitive to carbon dioxide than most previous estimates.

The research could solve one of the great unknowns of climate sensitivity, the role of cloud formation and whether this will have a positive or negative effect 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 UNSW's Centre of Excellence for Climate System Science, Professor 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 narrower but much higher estimate can be found in the observations around the role of water vapour in cloud formation.

Observations show when water vapour is taken up by the atmosphere through evaporation the updraughts often rise up to 15 km to form heavy rains, but can also rise just a few km before returning to the surface without forming such rains.

In addition, where updraughts rise this smaller distance they reduce total cloud cover because they pull more vapour away from the higher cloud forming regions than when only the deep ones are present.

Climate models that show a low global temperature response to carbon dioxide do not include enough of this lower-level process. They instead simulate nearly all updraughts rising to 15 km.

These deeper updraughts alone do not have the same effect, resulting in increased reflection of sunlight and reduced sensitivity of the global climate to atmospheric carbon dioxide.

However, real world observations show this behaviour is wrong.

When the processes are correct in the climate model, this produces cycles that take water vapour to a wider range of heights in the atmosphere, causing fewer clouds to form in a warmer climate. This increases the amount of sunlight and heat entering the atmosphere and increases the sensitivity of our climate to carbon dioxide or any other perturbation.

When water vapour processes are correctly represented, the sensitivity of the climate to a doubling of carbon dioxide - which will occur in the next 50 years – means we can expect a temperature increase of at least 3°C and more likely 4°C by 2100.

"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 Professor 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."

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ceirano | Friday, January 10, 2014, 3:33 PM
Why are people still putting this great lie about. It's finished, It's an absolute hoax. Get used to it. Look forward to a great future of inventiveness & innovation that will change our lives for the better.
Graeme | Monday, January 13, 2014, 7:58 AM
Seriously, the more evidence found that shows that the earth has been cooling the more outrageous the claims of global warming become. Even after an IPPC rep said that there had been no global warming for years. Has anyone heard about the Polar Vortex?
Despairing | Monday, January 13, 2014, 1:08 PM
Sigh. Climate change will lead to increased episodes of extreme weather such as your polar vortex. obviously neither of you have descendants to care about, given you don't care for their future. You can have your opinion but you can't deny facts. Do some research, why don't you?
Ken Goldsmith | Tuesday, January 14, 2014, 8:51 AM
Climate changes, has done before industrial revolution, will do regardless of small CO2 contribution by mankind. IPCC agreed Facts: NO warming since 1998.Northern Winter '11-'12 saw record Arctic ice accumulation. The actual measured Global Temperature is near the bottom of the warmist prediction range, and projects to fall through the bottom of the range soon. Sea levels have not been increasing as predicted, and rise is decelerating. All IPCC agreed facts. As Graeme wrote, the worse the evidence for warming, the more outrageous the claims. Perhaps YOU should do some research, Despairing?
ceirano | Wednesday, January 15, 2014, 9:46 PM
Congratulations Graeme & Ken. You've obviously been listening & taken notice of the scientific evidence that unbiased scientists have reported.
Ken Goldsmith | Thursday, January 16, 2014, 10:17 AM
Thank you ceirano. It appears the big majority of technical people who read these pages are in agreement. I got the years wrong in this fact:"Northern Winter '11-'12 saw record Arctic ice accumulation". It was of course '12-'13, winter '11-'12 had the alarmists crowing that we were headed for their earlier prediction of an "ice free Arctic" in 2013. Well, they got that one wrong, too, but they won't learn.
Goldie | Monday, January 20, 2014, 3:29 PM
Modelling, in this case climate modelling is seen by some to be indisputable proof that what a group or individual may claim, will definitely happen. Models of any kind will only give you an idea of 'what might' happen when a given set of data is entered into a model that has been independently verified as being capable of managing the required computation. They can and frequently are used as a tool to convince others of an outcome as we are seeing with the climate predictions. If a person was so inclined it would not be difficult to manufacture an outcome that supports an opinion by simply manipulating the data inputs or being selective about where you source your inputs in order to deliver the results you want. I think people have every right to be sceptical about the dire predictions being made about what the temperature will be in 86 years time if certain measures are not taken. It is perhaps convenient that people espousing such claims will not be around the answer if things don't go to script.