text: The temporal analysis revealed the evolution of public discourse from 2009 to 2018. In both 
  discourses, political discussions gradually faded, indicating a trend in the public perception of climate 
  issues to seeming slowly return to the scientiﬁc dimension in general. In 2009, political discussion was 
  the second most important topic in the global warming discourse, but its ranking fell to last in 2018. 
  In the climate change discourse, as shown in Figure 3, the association to political hashtags disappeared 
  in the recent two years. These ﬁndings seem to contradict earlier studies suggesting noticeable political 
  polarization in the climate discussion [66,93] and a Pew report saying that the partisan divide had 
  widened in terms of attitudes toward climate change issues [94]. We suggest a probable reason 
  responsible for this contradiction: Although political clusters in both discourses were shrinking, in the 
  climate change discourse, the proportion of red associations started to increase in recent years, as 
  shown in Figure 5a. The red cluster is a topic cluster with blurred edges and is composed of diverse 
  hashtags, such as “healthcare”, “education”, “poverty”, “innovation”, and “politics”. We examined 
  the tweets with these co-occurrences and found that although few typical political hashtags such as 
  “p2” and “tcot” were used, most of these tweets had strong political intentions. For example, when the 
  public noticed that whitehouse.gov no longer provided speciﬁc pages for climate change as well as 
  healthcare, LGBT rights, and civil rights in January 2017 [95], the red cluster expanded, as shown in 
  Figure 5a, and a large amount of co-occurrences among these issues emerged to blame the government’s 
  wrong practices of neglecting all these issues. We observed that “climatechange” occurred often 
  with hashtags such as “education”, “poverty”, “economy”, “leadership”, and “innovation” as the 
  object of the verb “rethink” in a large amount of tweets arguing for the government’s reﬂections on 
  several domestic policies. Thus, we think that climate politics did not disappear but changed their 
  form in public discussions in the last two years of the studied decade. A kind of discourse alliance 
  formed among climate change and several other domestic political issues to show political appeal 
  together, where a trend of pan-politicization rather than de-politicization might be identiﬁed in climate 
  change discussion. 