Worst-case climate change scenarios likely to be most accurate

8th December 2017

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Todd Heller

Climate change models are thought to be underestimating future levels of global warming, with severe forecasts likely to be the most accurate.

That is according to a new study published in the scientific journal Nature, which estimates there is a 93% chance that global warming will exceed 4˚C by the end of this century under a business-as-usual scenario.

That is double the target set in the Paris Climate Agreement to keep temperature rises below 2˚C above pre-industrial levels, with previous models only putting the likelihood of a 4˚C rise at 62%.

The researchers said the different variations in global warming projected by models were largely due to how they simulate changes in clouds reflecting heat from the sun back to space.

Some models suggest this cooling effect could increase in the future, while others suggest it might decrease.

However, it was discovered that the models that best replicate how energy has flowed from earth to space in the recent past, tend to project greater-than-average warming in the future.

“It makes sense that the models that do the best job at simulating today’s observations might be the models with the most reliable predictions,” study co-author, Ken Caldeira of the Carnegie Institute for Science, said.

Raw climate model results show that if emissions follow a business-as-usual scenario, global temperatures will increase between 3.2˚C and 5.9˚C by the end of this century

But by comparing models, the researchers eliminated the lower end of this range, finding that the most likely warming is about 0.5˚C greater than the raw results suggest.

Study co-author, Patrick Brown, said that it “doesn’t make sense to dismiss the most-severe global warming projections based on the fact that climate models are imperfect”.

“On the contrary, if anything, we are showing that model shortcomings can be used to dismiss the least-severe projections,” he added.


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