text: Figure 3 depicts the associations of hashtags in the climate change discourse for each year 
  from 2009 to 2018. The scientiﬁc hashtags cluster (in green) was the most important theme in the 
  climate change discourse, especially more recently. However, some scientiﬁc hashtags, such as “ghg” 
  (greenhouse gas), “co2”, and “forests”, were not identiﬁed in the scientiﬁc cluster but in the global 
  actions cluster (in yellow) because these hashtags were frequently used in the global action context and 
  identiﬁed with a closer semantic association to global action by Gephi. In addition to these hashtags, 
  the global action cluster included a series of international activities, such as “ipcc” (Intergovernmental 
  Panel on Climate Change), “unfccc” (United Nations Framework Convention on Climate Change), 
  and “cop” (Conferences of the Parties) for almost every year. The blue cluster includes to political 
  hashtags, such as “uniteblue”, “sgp”, “p2”, and “tcot”. In 2017 and 2018, the associations with political 
  hashtags disappeared among the top 50 hashtags. The small red cluster had a mixed theme, combining 
  “technology”, “innovation”, “education”, “africa”, “healthcare”, and “politics”. The centrality sum of 
  the nodes in the red cluster remained rather low throughout the 10-year period but obviously increased 
  in the last two years of the period according to Figure 5a. 