Int. J. Environ. Res. Public Health 2020, 17, 1062 2 of 22
complex changes in the state of the climate [7], which may be caused by natural process, external forces,
or human interventions [8]. By randomly assigning respondents to climate change or global warming
questionnaires, scholars conﬁrmed that the diﬀerent connotations contained in the two deﬁnitions are
likely to evoke distinct interpretations of the causes and impacts of the global climate issue [9], which
may inhibit collaboration and joint eﬀorts to mitigate the global challenge.
Public preference between climate change and global warming is even more apparent when
considering the ideology spectrum [ 10]. Some scholars concluded that conservatives, who are
less concerned with environmental issues, tended to use global warming as a narrative strategy
because global warming has a more direct connection with temperature rise, making it easier to ﬁnd
contradictory cues such as freezing weather or heavy snowstorms to deny global climate change
facts [11]. The associations between global warming and human activities may contribute to more
controversies as well [12], connecting global warming more with the “hoax” frame [5] and evoking
greater negative sentiment [13].
Although these existing studies have often attempted to identify the diﬀerences between these two
terminologies, only a particular few perspectives, such as sentiment, ideological preference, or cause
and eﬀect, were examined in each study [3,9,13]. However, the associate network model introduced by
psychologists suggests that human recognition and memory have a network-shaped architecture [14],
where individual understanding of particular objects is connected with numerous other objects in
the mind. According to the associate network model, individual understanding of the global climate
concern is a network composed of numerous inter-connected concepts, in which climate change and
global warming. As the two terminologies concern the primary mechanism of the global climate issue,
the preference between the two understandings may represent two distinct climate discourses by
diﬀerently organizing numerous climate concepts. Examining the diﬀerences between two discourses
with an associative perspective may provide communicators with unique insights into narrowing the
cognitive discrepancy. The temporal dimension was lacking in existing studies, necessitating the study
of how concepts associated with each other have evolved with time.
Large amounts of user-generated data on social media, which have been valued in computer science,
communication, and environmental studies [5,9,15–18], have enabled the acquistion of the social media
representation of the two discourses in a decade. In this study, by analyzing hashtag co-occurrence
patterns in 6,662,478 tweets containing “climate change” and “global warming” between 1 January 2009
and 31 December 2018, two semantic networks of public climate discourse were constructed to identify
the critical concepts and links surrounding the two terminologies. We conducted temporal analysis to
observe the evolution of the two discourses and to measure whether the discrepancy between the two
has widened or narrowed within the 10-year period.
To be speciﬁc, we formulated three research questions (RQs) to be explored in this study:
RQ1: What is the diﬀerence in how the two the discourses are associated with important climate
concepts in people’s minds?
RQ2: How did the two competing climate discourses evolve from 2009 to 2018?
RQ3: Did the two competing discourses converge or diverge in this decade?
2. Background
2.1. Climate Change, Global Warming, and Frames
Existing studies have noted that the subtle diﬀerence between climate change and global warming
evokes diﬀerent public cognitive responses, where global warming“indicates heat-related impacts,
human causes, increased UV light penetration, ozone depletion, and the greenhouse eﬀect, whereas