Computer models used to simulate what heat-trapping gases will do with global temperatures have been quite punctual in your predictions, a new study found.
After years of listening to critics, they have discovered the accuracy of models, climate scientist Zeke Hausfather decided to see how good they have been. He located 17 models used between 1970 and 2007 and found that most of them predicted results "indistinguishable from what actually happened."
"In general, our models got it right, a little bit," said Hausfather, UC Berkeley scientist, climate and energy director at UC Berkeley. Innovative Institute. "If they get it wrong, it's a little hot, but I wouldn't read much about it."
Ten of the 17 were close to the temperatures that actually happened, said Hausfather, lead author of a study in Wednesday's magazine Geophysical Research Letters.
But scientists really got physics right even more than that, Hausfather said.
Climate models are based on two main assumptions. One is the physics of the atmosphere and how it reacts to heat-trapping gases. The other is the amount of greenhouse gases released into the air.
Scientists were sometimes wrong in their predictions about the growth of carbon pollution, saying there would be more gases than there really are, Hausfather said. If the amount of heat-trapping gases is wrong, the temperatures are wrong.
So Hausfather and colleagues, including NASA climate scientist Gavin Schmidt, analyzed the performance of models only in pure science, eliminating the emission factor. By that count, 14 of the 17 computer models accurately predicted the future.
Scientists also gave each computer simulation a "skill score" that essentially assigned a percentage to each. The average grade was 69%.
One of the first computer models, manufactured in 1970, obtained 91%. Most striking is that, at the time, climate change was not noticeable in the annual temperature records as it is now, Hausfather said.
Stanford University climate scientist Noah Diffenbaugh, who was not part of the study, called the work creative and the results were impressive.
"Even without knowing what the current level of greenhouse gas concentration would be, climate models very well predicted the evolution of global temperature," said Diffenbaugh.
It is crucial that these models are accurate because "we have a planet Earth so that we cannot conduct controlled experiments on the real climate system," he added.
University of Illinois Climate Scientist Donald Wuebbles, who also did not participate in the study, said climate change deniers "do a lot of weird things to misrepresent models. None of these analyzes was valid and should be ignored. We should no longer debate the basic science of climate change."