“We’re not really sure,” 

"As for his latest work, Li noted that the results might be model-dependent, so further modeling is necessary to confirm the results."
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to be science a theory must withstand rigorous testing and is considered false if just one contradiction is discovered.  gorebull climate hoaxers have used hundreds of models and still none of their computer models have correctly predicted observed results.  in science, hundreds of failed computer models indicate sloppy scholarship or manipulated data. 
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it's not science when you rely on failed computer models and failed theory to explain why gorebull climate hoaxers should control the world's energy, economy and wealth.  it's called religion.