text: **Table 2.**Hashtags that remained on the top 50 list for the climate change or the global warming 
  discourse from 2009 to 2018. 
  
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              [html]<thead><tr><td></td><td>Unique</td><td>Shared</td></tr></thead><tbody><tr><td># climatechange</td><td>china, solar, water, food, economy, coal, sustainability</td><td>co2, news, carbon, green, climate,</td></tr><tr><td># globalwarming</td><td>pollution, earth</td><td>us, energy, science, environment</td></tr></tbody>
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  Figures 3 and 4 show the overall evolution of critical hashtags’ associations in the 10-year period, 
  where the nodes in the 10 graphs are located in the same position but the strength of associations varies 
  across longitudinal time. Vector graphics with the label of nodes are provided in the Supplementary 
  Materials. Four themes were identiﬁed in each discourse according to the nodes’ associations. To more 
  explicitly demonstrate the relative importance of each cluster in each year, we calculated the sum of 
  the degree centrality of all the nodes belonging to each cluster and their change in centrality over the 
  10 years, as shown in Figure 5. 