Int. J. Environ. Res. Public Health 2020, 17, 1062 13 of 22
issues and re-constructing them diﬀerently. By comparing the persistent words used related to the two
discourses in the 10-year period in Table 2, we think that global warming showed a relative preference
toward general descriptions or slogans, such as “earth” and “pollution”, whereas “climate change”
was more associated to speciﬁc issues like “solar”, “coal”, “china”, and “food”.
Studies have suggested that the public shows a preference for scientiﬁc publications with general
keywords compared with those with complicated scientiﬁc jargon [47], lacking a deep understanding of
the complicated issue [46] and the necessity for mitigation of the climate issue [47]. These conclusions
seem to suit global warming more than climate change according to the current study, which is
probably because climate change receives more publicity and recognition than global warming in the
scientiﬁc community. In the association network shown in Figure 2, global warming was found to be
more connected with temperature abnormalities. This ﬁnding is in accordance with studies reporting
that short-term temperature anomalies [87] can increase the public’s belief about global warming by
increasing the understanding of this abstract issue [88], although scientists mostly make judgments
based on long-term weather statistics [ 89]. However, none of the four words, “snow”, “summer”,
“winter”, or “heatwave” in the temperature theme of global warming were ranked in the top 50 nodes
list of the climate change network.
Even when climate change and global warming shared concern about similar topics such as the
cause of the climate issue, global warming tended to focus on carbon emission phenomena, whereas
climate change preferred a more in-depth perspective, highlighting the importance of global action
to mitigate the climate issue in its second-largest cluster, with energy structure as the contributor to
carbon emissions in its third largest cluster. As invisible causes and disbelief in actions have long
been regarded as two key reasons for low climate concern [ 90], the two terminologies’ diﬀerences
in connotations suggest that introducing these absent sub-topics into global warming discourse or
highlighting climate change for its inherent connotations may help communicators raise public concern
about climate.
5.1.2. Political Connotations
Studies noted that frame preference between climate change and global warming reﬂects
individuals’ ideological spectrum, where climate change and global warming were favored by
the liberals and conservatives, respectively [10]. The cluster analysis of the semantic network in the
current study demonstrated that global warming triggered far more political responses than climate
change. The second largest cluster of global warming was politics-based, where hashtag “tcot”, favored
by right-leaning users and “p2”, favored by left-leaning users, were both ranked in the list of top nodes
of the global warming discourse, but neither was included in the list of top nodes of the climate change
discourse. Considering that earlier ﬁndings suggested that global warming was more likely to be used
by conservatives to question the reality of climate issue [11] and climate change is more commonly
adopted when discussing action against the climate change issue [5], global warming had a stronger
political connotation in public discussion.
5.1.3. Discourse Structure
In the discourse surrounding #climatechange, “environment”, “energy”, and “global action”
represented the themes of the three largest clusters in the network. However, three popularly recurring
hashtags, “#environment”, “#energy”, and “#climateaction”, did not belong to any of the three clusters
above, but formed another small tight cluster together, sitting in the most central part of the semantic
network, as shown in Figure 2b. As each of the three hashtags can almost represent one sub-theme of