analysis showed that the associations between the two discourses were correlated in the 10-year period
(the p-value for 2015 was 0.011; p-values for all the other years were less than 0.001). Figure 6b reveals
that the similarity of associations between the top 50 nodes in the two discourses ﬂuctuated and did
not show a rising trend with the correlation of nodes’ rank order.
Int. J. Environ. Res. Public Health 2020, xx, 5 12 of 22
(a)
 (b)
Figure 5. The sum of centrality for nodes in four clusters in the climate change discourse from 2009 to
2018 (a); (the sum of centrality for nodes in four clusters in the global warming discourse from 2009 to
2018 (b).
As the climate change and global warming discourses evolved over the past years, their relative
statuses in public discourse also changed. Although from 2009 to 2018, increasing numbers of people
started to use Twitter, resulting in an overall rise in the number of tweets and hashtags, the ratio of
#climatechange frequency and #globalwarming frequency still indicated the public’s change in frame
preference. Figure 1a displays that in 2009, the number of tweets with #climatechange was 2.69 times
that of the tweets with #globalwarming, whereas the ratio signiﬁcantly since 2013 and reached 13.02
in 2018. The climate change network showed a stronger ability to incorporate diverse hashtags into
discussions, according to Figure 1b. In 2009, the hashtags that co-occurred with #climatechange were
2.44 times those that co-occurred with #globalwarming, and the ratio climbed to 6.36 in 2018.
The rank–order correlation coefﬁcient of nodes between the two networks maintained a stable
level and showed a slight climbing trend starting 2009, as shown in Figure 6a, except for 2010 and
2011, when the p-values were larger than 0.05 and no signiﬁcant correlations were identiﬁed. The QAP
analysis showed that the associations between the two discourses were correlated in the 10-year period
(the p-value for 2015 was 0.011; p-values for all the other years were less than 0.001). Figure 6b reveals
that the similarity of associations between the top 50 nodes in the two discourses ﬂuctuated and did
not show a rising trend with the correlation of nodes’ rank order .
(a)
 (b)
Figure 6. Rank order correlation between hashtags in the climate change and global warming discourses
from 2009 to 2018 ( a); correlation between matrices of the climate change discourse and the global
warming discourse from 2009 to 2018 (b).
5. Discussion
5.1. Themes and Structure of the Two Discourses
5.1.1. Phenomenon vs. Mechanism of Action
Climate change and global warming have long been two competing frameworks shaping the
public’s perceptions, memory, and interpretations of climate issue by highlighting different aspects of
Figure 6. Rank order correlation between hashtags in the climate change and global warming discourses
from 2009 to 2018 ( a); correlation between matrices of the climate change discourse and the global
warming discourse from 2009 to 2018 (b).
5. Discussion
5.1. Themes and Structure of the Two Discourses
5.1.1. Phenomenon vs. Mechanism of Action
Climate change and global warming have long been two competing frameworks shaping the
public’s perceptions, memory, and interpretations of climate issue by highlighting diﬀerent aspects of