Research Wallace to see if he is an authority on global warming.
In this case, the student is using a secondary source of information, as the Arnie Wallace is a writer who offers her own opinion in regards to the information she can collect about global warming.
The best way the reader can determine the credibility of the information contained in the student's essay is to check Arnie Wallace's work and revise the sources she has cited for her writing. If the sources Wallace uses come from a reliable primary source, then the information contained in the student's essay is credible.
