text: A temporal analysis was introduced to understand the evolution of the two climate discourses 
  over a long period. We ﬁrst examined how the two semantic networks evolved in the past years. 
  All the nodes once ranked top 50 in any of the 10 years were gathered to form a union set for each 
  dataset. Then, they were clustered according to the strength of their associations in the whole dataset 
  and mapped with a force-directed layout algorithm in Gephi to produce a graph of nodes. With the 
  dynamic network function supplied by Gephi, we then added the associations between the nodes 
  ranked on the top 50 list in 2009 to the graph of nodes and obtained the relationship of the top 50 nodes 
  for 2009. Similarly, we produced a total of 10 graphs from 2009 to 2018, where the positions of the 
  nodes on the 10 maps are the same, but the strengths of their associations are diﬀerent to represent the 
  changes in the associations of key hashtags for each discourse. 
  
  The correlation between climate change and global warming discourses was measured every 
  year to observe whether the two discourses converged or diverged over time. Considering computing 
  power limitations, only key hashtags ranked in either of the top 50 lists for the two discourses in that 
  year were included in the calculations. First, we measured to what extent the two discourses resemble 
  each other in the order of importance for the hashtags in each year. For every year, the top 50 hashtags 
  in each network were selected with a rank order according to their centrality. Then, Spearman’s rank 
  correlation coeﬃcient was used to examine the correlation of the rank orders of the selected nodes 
  in the two discourses [84], where a high Spearman correlation indicates that the hashtags in the two 
  discourses were ranked similarly. Secondly, we measured to what extent the two discourses resembled 
  each other in the associations between the key hashtags for each year. For every year, we obtained the 
  union of the two top 50 nodes lists and used the name of the nodes in the union as the row name and 