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make global action salient for people talking about global warming than people talking about climate
change [40], even though the facts of climate issues are highly recognized in both discourses.
6. Conclusions
As social media is gradually overtaking the role of legacy media providing a forum for public
discussion, the semantic associations contained in social media discussions reﬂect and reinforce how
individuals portray global climate issues. By examining hashtag co-occurrence patterns on Twitter
between 2009 and 2018, we identiﬁed distinct climate perceptions hidden behind two competing
climate discourses and discovered how these two discourses evolved.
We found that broad scientiﬁc, social, political, and international discussions are the topics
of public climate discourse. Although the semantic di ﬀerence between climate change and global
warming seems subtle, the di ﬀerences in their cognitive associations are not trivial. Despite some
shared concerns between the two discourses, “global warming” is more politicized and focuses more on
general phenomena, especially temperature abnormalities, whereas climate change is a more compact
topic with a more scientiﬁc perspective and tends to refer to speciﬁc issues. The temporal analysis
revealed that traditional political discussions decreased in both discourses but climate change started to
build a discourse alliance with diverse domestic issues to show political intentions. Global warming’s
associations to extreme events and temperature change were suddenly strengthened around 2012.
Climate change is becoming dominant compared with global warming in public discussions. Although
the two discourses are becoming increasingly similar in the rank order of climate concepts, a notable
discrepancy still exists in the way in which they get concepts associated. These observations may
provide climate communicators with theoretical and practical hints to narrow the discrepancy between
diverse climate perceptions.
Limitation and Future Directions
Though big data allowed us to decrease the bias by dealing with the whole set of social media
data rather than samples, discrepancies still exist between social media users and the public. As most
Twitter users do not disclose their age, education, income, and gender in users’ proﬁle, demographics
were not introduced as moderator factors in this study. Previous studies noted that in 1970s, global
cooling was a prominent climate concern amongst the public [105]. While in the 1980s, ozone layer
depletion, species extinction and rainforest destruction became salient on the mass media agenda [106].
Considering the historical background of climate issues, age might inﬂuence how individuals perceive
climate issues. According to the statistics in 2017 [ 107], only 16 % of older people (older than 60)
in America use Twitter, while the proportion is 39% for people between 30–59 years old and 47%
for people younger than 30 years old (Stastista, 2017). Our results reﬂect the climate perception of
older people who use Twitter, as well as younger people amongst whom Twitter is more popular.
Although some scholars reported that it is statistically reliable to take data on Twitter as a substitute
and supplement for polling [108], we thought our results should be further examined before being
generalized to the whole population.
In this study, we characterized the di ﬀerences between two popular climate discourses and
examined how two discourses evolved over a 10-year period. We did not focus on the interactions
between public climate discourse and external factors. However, the evolution of climate discourse
might be driven by several external forces such as scientiﬁc e ﬀorts, natural events, politics and
online information (or misinformation) campaigns. The prevalence of certain climate concepts may
inverse be weaponized to cause rhetorical shifts in politics and science popularization. For instance,