text: The hypothesis proposed by [43] suggests that language production may reﬂect lexical association, 
  and the more often two concepts are simultaneously mentioned in a piece of text, the higher the 
  chance that the two concepts are associated in the individual’s cognitive map of the world. Therefore, 
  semantic network analysis, a methodology based on cognitive science, could help researchers infer 
  the hidden cognitive network structure in the human mind [44] based on the analysis of texts, as the 
  frequency, semantic distance, and co-occurrence pattern of words can accurately reﬂect their meaning 
  and links [45]. Several researchers have attempted to build a semantic network of certain climate 
  events in social media discourse and scientiﬁc publications [46–48]. Research about public perceptions 
  of global climate change in Qatar conﬁrmed that the observed semantic network of climate concepts is 
  not random and represents as meaningful clusters [49]. 
  
  2.3. Hashtags as Frame Vehicles on Social Media 