Computer models used to simulate what heat-trapping gases will do to global temperatures have been largely accurate in their predictions, a study published on Wednesday said.
Climate scientist Zeke Hausfather tracked down 17 models used between 1970 and 2007 and found that the majority of them predicted results that were “indistinguishable from what actually occurred.”
“By and large our models have gotten it right, plus or minus a little bit,” said Hausfather, a University of California, Berkeley scientist who is climate and energy director at the Breakthrough Institute.
“If they get it wrong, it’s slightly on the warm side, but I wouldn’t read too much into that,” Hausfather said.
Ten of the 17 were close to the temperatures that actually happened, said Hausfather, lead author of the study in the journal Geophysical Research Letters.
However, scientists actually got the physics right even more than that, Hausfather said.
That is because they make two main assumptions when they model what will happen: One is the physics of the atmosphere and how it reacts to heat-trapping gases and the other is the amount of greenhouse gases put into the air, he said.
A few times, scientists were wrong in their predictions about the growth of carbon pollution, saying there would be more of the gases than there actually were, Hausfather said.
If they got the amount of heat-trapping gases wrong, they then got the temperatures wrong, he said.
So Hausfather and colleagues, including NASA climate scientist Gavin Schmidt, looked at how well the models did on just the pure science, taking out the emissions factor. On that count, 14 of the 17 computer models accurately predicted the future.
The scientists also gave each computer simulation a “skill score” that essentially gave a percentage grade to each one. The average grade was 69 percent.
One of the earliest computer models, made in 1970, got a 91 percent.
What is so impressive about that is that at the time, climate change was not noticeable in the yearly temperature records like 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 striking.
“Even without knowing what the current level of greenhouse gas concentrations would be, the climate models predicted the evolution of global temperature quite well,” Diffenbaugh said in an e-mail.
It is crucial that these models are accurate because “we have one planet Earth, so we can’t conduct controlled experiments on the actual climate system,” Diffenbaugh said.
University of Illinois climate scientist Donald Wuebbles, who also was not part of the study, said that climate change “deniers do a lot of weird things to misrepresent models. None of those analyses have been valid and they should be ignored. We should no longer be debating the basic science of climate change.”
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