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then the associations suddenly strengthened in 2012 when numerous hashtags about phenomena were
included in the discourse. Notably, the red node in the top right-hand corner named “2012” refers
to the Maya prediction that the year 2012 would be the end of the world and that the world would
be destroyed by extreme natural events, and was linked to other climate hashtags for the ﬁrst time
in the graph exactly in 2012. The blue nodes included the political hashtags, such as “maga”, “ows”,
“p2”, “tcot”, and “obama”. The involvement of political hashtags in the global warming discourse was
signiﬁcantly higher than that in the climate change discourse according to the comparison between
Figure 5a,b. From 2009 to 2018, the number of associations with political hashtags (blue nodes) faded,
as shown in Figure 4, and its importance in the semantic network gradually decreased, as shown in
Figure 5, except for variation in 2014. The yellow nodes describe the hesitation about climate facts
and actions, where words describing global efforts, such as “ipcc”, “cop15”, and “un”, and words
questioning global warming, such as “hoax” and “fraud”, were both included. The associations
between the yellow nodes were most salient in 2010 and 2011 but were less dominant in the following
years. The green nodes occupied 50.7% of all the nodes representing talk about the scientiﬁc hashtags of
climate issue, including words such as “ecology”, “ocean”, and “cleanenergy”. Associations between
scientiﬁc hashtags (green nodes) exploded and the centrality sum of this cluster also showed an
obvious rising trend in dominating the theme of the global warming discourse, according to Figure 5.
Figure 3. Association network of top 50 nodes of climate change for each year from 2009 to 2018.
Figure 4. Association network of top 50 nodes of global warming for each year from 2009 to 2018.
Figure 4. Association network of top 50 nodes of global warming for each year from 2009 to 2018.