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Climate Uncertainty Reduced

By Stephen Luntz

A new way of estimating the uncertainty of the Earth’s average temperature for the rest of this century anticipates warming very similar to predictions by the Intergovernmental Panel on Climate Change (IPCC) while narrowing the uncertainty.

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However, the modelling uses only known processes, leaving out tipping points such as a sudden release of methane from permafrost.

“The IPCC used 20 models and estimated uncertainty from the range,” says Prof David Karoly of the University of Melbourne. However, the models did not consider the way the carbon cycle is affected by interactions with the oceans and land surface. Extra uncertainty was added to allow for this.

Karoly and Dr Roger Bodman of Victoria University used a simpler model but added these carbon cycle factors. They then used not only 20th century temperature observations to constrain their model, as is standard, but past observations of carbon dioxide variations.

By considering these neglected factors Karoly and Bodman have shown that we are only likely to exceed a 6°C temperature increase by 2100 if human-induced warming triggers a runaway effect they could not model. However, the pair also reveal that it is even less likely than previously recognised that temperatures will remain within the globally agreed target of 2°C of pre-industrial levels without substantial action to stem emissions.

“The model was not constrained to produce the same median warming as the IPCC’s average,” Karoly says, but the findings on this point were effectively identical. The research was published in Nature Climate Change.


The full text of this article can be purchased from Informit.