More severe global warming predictions are likely more accurate

"Our results suggest that it doesn't make sense to dismiss the most-severe global warming projections," climate scientist Patrick Brown said.
By Brooks Hays  |  Dec. 7, 2017 at 9:27 AM
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Dec. 7 (UPI) -- Researchers say climate models used by the United Nations' Intergovernmental Panel on Climate Change are likely underestimating the amount warming the planet will experience by the end of the century.

According to a new study published this week in the journal Nature, models that predict more severe global warming outcomes better reflect observations of the current climate.

"There are dozens of prominent global climate models and they all project different amounts of global warming for a given change in greenhouse gas concentrations, primarily because there is not a consensus on how to best model some key aspects of the climate system," Patrick Brown, a climate scientist with the Carnegie Institution for Science, said in a news release.

Climate models predict Earth will warm between 5.8 and 10.6 degrees Fahrenheit by the end of the century if changes aren't made to curb carbon emissions. The difference between the bottom and top of the prediction range nearly equals a factor of two.

To find out which end of the range is more likely, scientists dissected several of the most popular climate models and teased out the most important factors in each. Brown and his research partner Ken Caldeira wanted to see which model components were most capable of predicting climate change in the past.

The duo looked at how the models accounted for the flow of energy from Earth to space, both spatially and seasonally. The models that synced most accurately with energy flow patterns in the past tended to offer warming predictions on the upper end of the range.

"Our results suggest that it doesn't make sense to dismiss the most-severe global warming projections based on the fact that climate models are imperfect in their simulation of the current climate," Brown said. "On the contrary, if anything, we are showing that model shortcomings can be used to dismiss the least-severe projections."

Clouds account for the major discrepancy between models on either side of the warming prediction range. Some models predict an increase in cloud formation, which would reflect the suns rays back into space and offer some cooling relief. Others predict the opposite.

The latest research suggests the models that most accurately predict today's climate patterns are the ones that predict less cloud cooling 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," Caldeira said. "Our study indicates that if emissions follow a commonly used business-as-usual scenario, there is a 93 percent chance that global warming will exceed 4 degrees Celsius -- 7.2 degrees Fahrenheit -- by the end of this century. Previous studies had put this likelihood at 62 percent."

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