The Impact of Message Source on the Effectiveness of Communications About Climate Change

Abstract

We conducted a survey experiment in which we presented 1,850 respondents with one of two versions of an appeal emphasizing either the threats to the environment or threats to national security of the United States as a result of climate change. The messages were attributed to one of four sources: Republican Party leaders, Democratic Party leaders, military officials, or climate scientists. The results reveal that messages attributed to military leaders, or to Republican Party leaders, can enhance the impact of the appeal. This finding underscores the importance that the source of any communication can have on its overall effectiveness.

Full text

The Impact of Message Source on the Effectiveness of Communications about
Climate Change
Toby Bolsen
Risa Palm
Justin T. Kingsland
Abstract
We conducted a survey experiment in which we presented 1,850 respondents with one of
two versions of an appeal emphasizing either the threats to the environment or threats to
national security of the United States as a result of climate change. The messages were
attributed to one of four sources: Republican or Democratic party leaders, military
officials, or climate scientists. The results reveal that messages attributed to military
leaders, or to Republican party leaders, can enhance the impact of the appeal. This
finding underscores the importance that the source of any communication can have on its
overall effectiveness.
Keywords: Climate change, framing, message source, public opinion
Citation: Bolsen, T., Palm, R., & Kingsland, J. T. (2019). The Impact of Message Source
on the Effectiveness of Communications About Climate Change. Science
Communication, 41(4), 464-487.
https://doi.org/10.1177/1075547019863154

Americans report deep divisions along partisan lines over fundamental beliefs
about whether human-caused climate change is real, the level of threat it poses, and
whether there is a need for action to reduce greenhouse gases. Despite an overwhelming
scientific consensus that climate change is human-caused and presents a major threat to
human societies and ecosystems (Cook et al., 2016), a significant percentage of
Americans do not believe that climate change is occurring (30%) or that it is human-
caused (42%) (Leiserowitz et al., 2018; also see, Egan & Mullins, 2017). Public
discourse on climate change continues to be characterized by partisan and ideological
divisions in the U.S. (Dunlap, McCright, & Yarosh, 2016; Feldman et al., 2012;
Hamilton, 2016; Hart et al., 2015). For example, one recent survey reported that while
95% of liberal Democrats believe that human-caused climate change is real, only 40% of
conservative Republicans say the same (Goldberg et al., 2019; Leiserowitz et al., 2018).
An important challenge for science communicators is how to effectively engage
individuals who reject information about climate change.
Varying the way that climate change messages are framed – that is, varying the
words, phrases or images that highlight specific aspects of climate change – has been
shown to affect the response of various audiences (Feldman & Hart, 2018;
Lewandowsky, Gignac, & Vaughan, 2013; McCright et al, 2016; Myers, Nisbet, Maibach,
& Leiserowitz, 2012; Nisbet & Mooney, 2007; van der Linden, Leiserowitz, & Maibach,
2019). For example, a communicator might bring attention to the environmental,
economic, public health, or national security implications of climate change, providing an
“interpretive storyline that set(s) a specific train of thought in motion, communicating

why an issue might be a problem, who or what might be responsible for it, and what
should be done about it” (Nisbet, 2009, p.15).
A growing body of research has examined how exposure to issue, or emphasis,
frames shape climate change beliefs (for a review, see Bolsen & Shapiro, 2017). Yet little
work explicitly manipulates the source of an appeal focused on shifting public opinion on
climate change.1 Are framed messages more impactful when they are associated with an
ostensibly credible source? Does the presence of a partisan source manipulation (e.g., in-
group versus out-group) condition the impact of the message?
We extend research on issue framing and social identity theory to generate
predictions about how the presence of a source cue (climate scientists, military leaders,
Democratic Party leaders, or Republican party leaders) in an appeal highlighting either
the environmental or national security effects of climate change conditions the
effectiveness of an appeal. We implemented a survey experiment to test how the
presence of different sources conditioned a frame’s impact on individuals’ climate-related
beliefs. The results suggest that the presence of specific sources linked with frames
highlighting different effects of climate change can increase or decrease the message’s
impact on individuals’ related beliefs. This underscores the importance that the source of
any strategic climate communication effort can have on its overall effectiveness, as well
as the need for credible and trusted opinion leaders to convey messages who have the
capacity to persuade skeptical audiences.
1 We discuss several exceptions below, including Benegal & Scruggs, 2018; Ehret, Van
Boven, & Sherman, 2018a; Van Boven, Ehret, & Sherman, 2018b; Kousser & Tranter,
2018.

Issue frames and climate change beliefs
A growing body of research has explored how exposing people to frames that
emphasize different aspects of climate change shape citizens’ related beliefs and
willingness to take actions that would reduce greenhouse gas emissions (Hart, 2011; Hart
& Feldman, 2016; Hart & Nisbet, 2012; Maibach, Nisbet, Baldwin, Akerlof, & Diao,
2010; Leiserowitz, 2007; Myers, Nisbet, Maibach, & Leiserowitz, 2012; Nisbet, 2009;
Villar & Krosnick, 2011). An issue or emphasis framing effect occurs when exposure to a
communication causes an individual to place relatively greater “weight” on the
emphasized consideration in the opinion formation process (Chong & Druckman, 2007).2
Exposure to framed messages may increase the availability, accessibility, and/or
perceived applicability of specific aspects of the complicated issue of climate change.
Myers et al. (2012), for instance, tested how exposure to one of three distinct frames
associated with the effects of climate change – national security, environment, and public
health – affected self-reported emotions among respondents with different levels of pre-
existing skepticism about climate change. They found that exposure to the public health
frame increased feelings of hope whereas the national security frame unexpectedly
increased anger among “doubtful” and “dismissive” audience segments. Myers et al.
(2012) stated that one factor that might have accounted for this “boomerang effect”3 was
the lack of the congruence between the messenger and the frame. They posited that
2 We focus exclusively on issue framing effects and not equivalency, or valence, framing
effects that occur when positive or negative information unconsciously influences
preferences as a result of a negativity bias in the encoding of stimulus information
(Kahneman & Tversky, 1979; for a typology of framing effects, see Levin, Schneider, &
Gaeth, 1998).

participants may have experienced anger at the experimenters for making claims about
the national security implications of climate change, and called for future work to explore
the role that the presence of sources linked with specific frames might have on different
audiences.
Frames that accentuate scientific consensus among climate scientists regarding
the existence of human-caused climate change have been found to increase belief in
human-caused climate change and support among Americans for policy action to address
the problem (Lewandowsky et al., 2012; van der Linden, 2015; van der Linden et al.,
2019). Other studies have demonstrated that highlighting its local impacts, for instance
through visual images showing flooding that would occur as a result of sea level rise in
coastal communities, can increase public concern and support for actions to address the
problem (Bolsen, Kingsland, & Palm, 2018). However, response to otherwise credible
and persuasive information can be undermined when presented in competition with
rhetoric that politicizes climate science, for instance by actors seeking to cast doubt on
the existence of a scientific consensus. (Bolsen & Druckman, 2018; Druckman, 2017;
McCright & Dunlap, 2011; McCright et al., 2016; van der Linden et al., 2017).
Source credibility, trust, and persuasion
While a number of experiments have documented the impact of exposure to
strategic frames on Americans’ climate beliefs, few studies have varied the presence of
3 Hart and Nisbet (2012, p. 704) state, “A boomerang effect occurs when a message is
strategically constructed with a specific intent but produces a result that is the opposite of
that intent”; (for other examples of such effects in climate communication studies, see
Cook & Lewandowsky, 2016; Myers et al., 2012; Zhou, 2016).

sources linked with a pro-climate action message to determine if such information
moderates a frame’s impact on individuals’ climate beliefs. Research on environmental
risk communication and issue-framing makes clear that the effectiveness of any message
depends crucially on the audience’s trust in and perception of credibility toward its source
(Brewer & Ley, 2013; Druckman, 2001a; 2001b; Liu & Priest, 2009; Priest, 2001; Renn
& Levine, 1991). Perceptions about the competence, expertise, objectivity, impartiality,
and fairness of a message’s source determine its persuasive impact, as well as other more
peripheral factors such as the attractiveness of the source, sympathy or empathy toward
the source, and social status of the source (Renn & Levine, 1991).
The “elaboration-likelihood model of persuasion” (ELM) has been applied by
social scientists across disciplines to understand the mechanisms by which risk
communication can generate persuasion (Petty & Cacioppo, 1986). The ELM
distinguishes between central and peripheral routes of persuasion. The peripheral route
involves the use of heuristics – such as the perceived credibility of a messenger – in
determining whether or not to accept a particular message; the central route is
characterized by more effortful information processing triggered by the motivation of an
individual to actively process the information (Brewer & Ley, 2013; Eagly & Chaiken,
1993; Renn & Levine, 1991).
Finally, empirical research has demonstrated the credibility of “scientists” as
generally credible sources. Surveys conducted in both the U.S. and among British
citizens has demonstrated that “scientists” tend to be among the most trusted sources for
providing accurate information about environmental issues in general and on climate

change in particular (Bickerstaff et al., 2008; Malka, Krosnick, & Langer, 2009; Nisbet &
Myers, 2007).4
Based on this literature, we hypothesize:
The presence of a credible source linked with a frame congruent with the
expertise attributed to this source will increase the frame’s impact on individuals’
beliefs. Specifically, climate scientists linked with a frame highlighting climate
change’s environmental effects will increase the frame’s impact on individuals’
related beliefs. (Hypothesis 1)
Similarly, military leaders linked with a frame that emphasizes climate change’s
effects on U.S. national security will increase the frame’s impact on individuals’
related beliefs. (Hypothesis 2)
Social identity theory and climate change beliefs
People derive their self-concept, in part, from the social groups and categories to
which they belong (Hogg & Reid, 2006; Huddy, 2001; Huddy, Mason, & Aaroe, 2015;
Kahan, 2016). These group attachments play a powerful role in shaping determinations
about the credibility and trust of any information source (Lenz, 2012; McCright,
Dentzman, Charters, & Dietz, 2013; Renn & Levine, 1991). Identity-based motivated
reasoning can lead audiences to interpret information about climate change in a biased
4 Partisanship, however, increasingly plays a role in perceptions about the credibility of
scientific information (Benegal & Scruggs, 2018; Gauchat, 2012; Motta, 2017), so it may
be that on a polarized issue such climate change some groups (e.g., Republicans) may not
find scientists to be the most effective source of any pro-climate appeal.

manner as a way to protect their existing beliefs or group attachments (Hart & Nisbet,
2012; Kahan et al., 2011).
One form of protection of social identity is the use of partisan motivated
reasoning (for a review, see Druckman, Leeper & Slothuus, 2018; Taber & Lodge, 2013;
Kahan, 2015). This process can occur when people possess strong opinions that guide
their reasoning strategies, or because of partisan cue-taking that simplifies and reduces
the amount of information and effort necessary to form an opinion in a given context
(Bartels, 2002; Bolsen, Druckman, & Cook, 2014; Cohen, 2003; Goren et al., 2009;
Guber, 2017; Kunda, 1990; Lelkes, Malka, & Bakker, 2019; Malka & Lelkes, 2010).
Partisans in pursuit of value-affirming information may therefore turn to sources who
share their group identity or cultural worldviews in seeking out or interpreting any new
information about climate change (Benegal & Scruggs, 2018; Feinberg & Willer, 2013;
Hmielowski et al., 2014; Kahan, Jenkins-Smith, & Braman, 2011)
Perception of consensus, particularly within ones’ close social network, also
influences people to align their beliefs with what they perceive to be the majority point-
of-view (Goldberg et al., 2019; Jost, 2018; van der Linden 2015). However, Americans
tend to underestimate the actual level of social consensus about human-induced climate
change (Mildenberger & Tingley, 2017). Empirical research has identified the power of
social consensus messages particularly among conservatives and Republicans. These
groups show a stronger drive for conformity to in-group norms and greater willingness to
adopt and share like-minded views with other Republicans (Benegal & Scruggs, 2018;
Goldberg et al., 2019; Jost, van der Linden, Panagopoulos & Hardin, 2018). In a recent
experiment that varied sources associated with a ballot proposal, Republicans were more

likely to support a climate proposal when it was endorsed by Republican party elites, and
perceptions that other Republicans also supported the initiative was a key mediating
belief (Ehret, Van Boven, & Sherman, 2018). In another recent study, a message
sponsored by Republican senators led Republican respondents to reject misinformation
about climate change, increase their belief in the existence of a scientific consensus, and
increase their belief that it is human-caused (Benegal & Scruggs, 2018). In these cases,
the partisan membership of the person delivering the message plays a powerful role in the
degree to which an appeal persuades any audience (Benegal & Scruggs, 2018; Ehret, Van
Boven, & Sherman, 2018; Kousser & Tranter, 2018; Li et al., 2016; Maibach et al., 2015;
Van Boven, Ehret, & Sherman, 2018).
Based on the findings of these studies, we hypothesize that:
The presence of an in-group (i.e., in-partisan) source regardless of the frame with
which it is associated will increase the frame’s impact on in-partisans’ related
beliefs.
(Hypothesis 3)
Data and methodology
We conducted a survey of 1,850 unique respondents recruited using Amazon’s
Mechanical Turk (MTurk) service in July 2018.5 Each participant was randomly
assigned to one of ten conditions that varied the content of an appeal accentuating either
5 MTurk samples offer greater diversity than student or other convenience samples and
have been used to replicate numerous studies across disciplines (Berinsky et al., 2012;
Mullinix et al., 2015). Descriptive statistics for the sample are available in a
supplementary file available upon request.

the environmental or national security risks of climate change (i.e., environmental or
national security frame). Two treatments were defined: one based on the threat that
climate change poses to the national security of the United States, and the second that
climate change poses for environmental sustainability. The national security treatment
emphasized the effects of climate change on human migration patterns and potential
“conflict over land ownership or water use that could result in war,” while the
environmental treatment emphasized coastal flooding due to sea-level rise and an
increased frequency of droughts and wildfires. In addition to highlighting these effects,
both treatments advocated action “to promote energy efficiency and renewable energy to
substantially decrease our greenhouse gas emissions.”6 We selected the environmental
frame given its dominance in climate discourses and the national security frame given the
and the call to link it with a credible source (e.g., Myers et al., 2012). The frames also
matched the domain of expertise for two of the sources we manipulated in the study.
To test the impact of the source, we assigned respondents to one of five groups.
For instance, the headline above the article in the no source (baseline) condition stated,
“Call for Action on Climate” and did not explicitly mention a source, whereas the other
conditions linked the appeal to a specific source – e.g., “Climate Scientists, Republican
Party Leaders, Democratic Party Leaders, or Military Leaders.” The appeal itself stated
that “Democratic Party leaders,” “Republican Party leaders,” “military leaders,” or
“climate scientists” were the ones highlighting these effects of climate change and calling
for policy action to reduce greenhouse gas emissions.
6 The complete wording of the stimuli for each condition and the survey instrument is
available upon request.

We measured how exposure to the treatments affected individuals’ beliefs about:
(a) the level of threat that climate change presents to national security (1-5 scale, none at
all / a great deal); (b) the level of threat that climate change presents to a sustainable
environment (1-5 scale, none at all / a great deal); and, (c) support for laws that promote
energy efficiency and renewable energy as a way to combat climate change (1–7 strongly
oppose / strongly support). The information that was employed across experimental
conditions highlighted one of these threats and called for a greater reliance on renewable
energy. As such, these measures serve as our primary dependent variables to evaluate
how message sources condition an appeal’s impact.
We also included several additional post-treatment measures. First, we measured
fundamental beliefs about climate change: (d) whether or not they believe climate change
is happening (1-7 Definitely not happening / definitely happening) and (e) the extent to
which they agreed with a statement that a scientific consensus exists regarding climate
change happening primarily as a result of human activity (1-7 strongly disagree / strongly
agree). Because our experiment explicitly manipulated the source of the message
highlighting the threats of climate change and need for policy action, we measured
respondents’ perceptions about (f) the degree to which political motives are a driver of
scientific research on climate change (1-7 strongly disagree / strongly agree). We
anticipate that audiences predisposed toward climate skepticism (e.g., Republicans) may
view messages from in-group sources about climate change as “less politicized”
compared to the same message without a source (or when attributed to an out-party
leader). Last, we measured respondents’ agreement with the statement (g) that the idea
climate change is primarily due to human activity is a hoax or a conspiracy (1-7 strongly

disagree / strongly agree). We included this item given the literature showing that
motivated reasoning processes appear to drive the expression of this relatively
widespread belief held by many Americans (i.e., estimated between 20%–40%) regarding
climate change (e.g., see Miller, Saunders, & Farhart, 2016; Uscinski, Klofstad, &
Atkinson, 2016; Uscinski & Parent, 2014). We anticipate similar dynamics resulting
from the source manipulation on climate hoax belief as with the other key measures – i.e.,
credible sources, or in-group/out-group sources, linked to an appeal highlighting the
threats of climate change will condition the impact of each message. Although belief in
conspiracies is a general predisposition (Lewandowsky, Oberauer, & Gignac, 2013;
Oliver & Wood, 2014), political ideology is strongly associated with which conspiracies
an individual will endorse (Uscinski & Parent, 2014). We expect that in-group sources
linked with a message highlighting climate change’s threats will decrease climate hoax
beliefs, whereas out-group sources may increase such beliefs among skeptical audiences
(i.e., Republicans who receive a message sponsored by Democratic Party leaders) as a
result of partisan motivated reasoning. We measured party identification on a 7-point
Likert scale, and then created a series of dummy variables for respondents who identified
as Democrat, Independent, or Republican.
Before turning to the results of our analyses, we include a condensed description
of our research design. Table 1 presents the framework of our experimental design, a
description of the treatments provided to respondents in each condition, and a restatement
of our hypothesized expectations.
[Insert Table 1 here]
Results

We evaluate the impact of the experimental treatments by regressing each
dependent variable on the experimental conditions, omitting the no-source appeal as the
baseline for each distinct appeal.7 Our design allows us to evaluate the effects of the
presence of two ostensibly credible, “expert” sources associated with each frame as well
as the impact of Republican and Democratic Party leaders.
The first column in Figure 1 reports the impact of the experimental conditions on
belief that climate change presents a threat to U.S. national security. First, in support of
Hypothesis 1, military leaders as the source of the message emphasizing climate change’s
threats to national security significantly increase the belief that climate change is a
national security threat across all respondents in the sample relative to the no-source
baseline (p = .04). We did not anticipate any effect of military leaders as the source of the
environmental message (Column 2, Figure 1) on beliefs that climate change presents a
threat to national security; however, as Figure 1 reports, military leaders linked with this
frame also significantly increased beliefs that climate change is a threat to national
security relative the no-source baseline (p = .01). Military leaders did not have an effect
on perceptions about the degree to which climate change presents an environmental threat
relative to the no-source baseline for that message. This suggests that the impact of a
source may depend on the degree to which the belief measured is in a domain in which
the source is perceived as an expert. Interestingly, in the full sample, military leaders
linked with a national security frame had no effect on support for a greater reliance on
renewable energy to reduce greenhouse gas emissions (Support Laws), as well as other
7 We report the means and standard deviations for each condition across all of the
dependent variables in a supplementary file available upon request from the
corresponding author.

beliefs we measured such as the belief climate change is happening, that a scientific
consensus exists, or that climate change is a hoax.
[Insert Figure 1 here]
The right side of Figure 1 reports the effects of the experimental conditions on
respondents’ belief that climate change presents a threat to a sustainable environment.
Hypothesis 2 predicted that climate scientists linked with an environmental message
would increase this message’s impact relative to the no source baseline. We find no
support for this hypothesis. We also find that when climate scientists are the source of a
message about the threat that climate change presents to national security and linked with
a call for policy action, respondents significantly reduced the strength of their beliefs
about the environmental threat climate change poses (p = .03), support for laws to
promote renewable energy (p = .04), belief that climate change is happening (p = .01),
and belief that a scientific consensus exists (p = .01).
The effects are even more dramatic when partisan information sources are
compared with the no-source baseline on the full sample. First, when Republican Party
leaders are the source of the national security climate message, respondents increase
their support for polices that would promote renewable energy to reduce greenhouse
gases (Support Laws) (p = .08). Republican sources linked with a national security
message reduced the perception that climate change research is driven primarily by
political motivations (p = .01). Further, Republican sources linked with this frame and
call for action also significantly decreased respondents’ perception that human induced
climate change is a hoax by nearly a one-half point shift on the five-point response scale
(p = .02). Source effects were more prominent in the national security frame conditions

compared to the environmental frame conditions. Nonetheless, when the environmental
message was attributed to Republican sources, respondents’ perceptions that a scientific
consensus exists on human-caused climate change increases (p = .09). On the other hand,
when the source of the national security message and call for action is attributed to
Democratic leaders, respondents became significantly less likely to see climate change as
a security threat (p = .10) and significantly less likely to say that climate change is
occurring (p = .03) or that a scientific consensus exists (p = .06).
To evaluate Hypothesis 3 regarding how in-group versus out-group partisan
sources may condition the impact of the experimental conditions on our dependent
measures, we replicate the analyses separately for Republican and Democrats in our
sample.8 First, we found very few significant treatment effects resulting from the source
manipulations when comparing Democrats in the no-source baseline condition to
Democrats across all other conditions (see Table 2 and Figure 2). There are a few
exceptions, such as military leaders having a significant positive effect on Democrats’
perceptions climate change is a national security threat, but the overall picture is that
Democrats in the baseline condition (and all source conditions) report highly skewed
beliefs that resulted in ceiling effects with little room for additional movement on many
of the response scales.
8 We chose this modeling approach rather than testing models with interaction effects
because we are interested (theoretically) in testing for source-effects associated with the
frames we introduce on Democrats (Republicans) in each condition relative to Democrats
(Republicans) in the No-Source baseline condition to examine within-subgroup effects.
We lack clear theoretical expectations for other estimation approaches that would rely on
Independents in the No-Source condition as a baseline for our hypothesis tests.

[Insert Table 2 and Figure 2 here]
Republicans tend to be more skeptical about climate change and less supportive of
laws to reduce greenhouse gases. However, we find that when Republican Party leaders
are the source of the environmental threat message, Republican respondents significantly
increased their belief that climate change is an environmental threat (Table 3, Model 2, p
= .03), that a scientific consensus exists (Table 3, Model 6, p = .04), and support for
polices that would increase a reliance on renewable energy to decrease greenhouse gas
emissions (Table 3, Model 4, p = .09). When Republican Party leaders are linked with
the national security message it significantly reduced Republicans’ perceptions that
climate change research is politically motivated by nearly a full point on the response
scale (Table 3, Model 1, p = .01) and decreased perceptions among Republicans that
evidence regarding climate change is a conspiracy or hoax (Table 3, Model 1, p = .09).
[Insert Table 3 here]
On the other hand, we find that when Democratic Party leaders are linked with the
environmental threat appeal, Republican respondents report significantly greater
perceptions that climate change research is politically motivated (Table 3, Model 1, p = .
05), and become significantly more convinced that climate change a hoax (Table 3,
Model 1, p = .05). In contrast, when Republican Party leaders are associated with the
national security message, Republican respondents were significantly less likely to
perceive climate science research as driven by political motivations (Table 3, Model 1, p
= .01).
Discussion and Conclusions

The U.S. public remains polarized along partisan and ideological lines on the
issue of human-induced climate change. Science communicators and others who seek to
build greater consensus thus face challenges both in securing the public’s attention to
important information (Lupia, 2013), as well as motivating skeptical audiences to
evaluate information in an “even-handed” manner with the goal of arriving at an
“accurate,” or correct, conclusion (Druckman, 2013; Druckman & Lupia, 2017).
We investigated an approach to communicating information about climate change
that involved manipulating the source of a message, while holding the content of the
message constant. We find that the presence of military leaders as a source of a pro-
climate appeal can significantly strengthen its persuasive impact, especially in the case of
an appeal emphasizing the effects of climate change on U.S. national security. Republican
Party leaders also enhanced the effectiveness of a frame both on average and among in-
group respondents, perhaps due to the surprising effect that unconventional or unexpected
sources of information can have in terms of its persuasive impact. Partisans making
statements that do not align with their perceived group’s position may draw greater
attention to the frame’s content, may be seen as a “costly” signal thereby enhancing its
perceived honesty and credibility, or may reduce identity protective forms of motivated
reasoning that would otherwise lead to the rejection of arguments related to a polarized
and highly salient issue such as climate change (Bengal & Scruggs, 2018; Druckman &
McGrath, 2019; Kahan et al., 2011; Kahan, 2015).
On the other hand, we found a perhaps surprising impact of one information
source: climate scientists. When climate scientists were linked with the national security
message it significantly reduced respondents’ perceptions about the threat of climate

change to national security, support for policy action, and perceptions of a scientific
consensus. Indeed when messages were attributed to climate scientists, they either had
no effect on most of the variables we tested, or their effect was a negative one. The call
by the American Meteorological Society for more engagement in policy communication
by climate scientists (https://amspolicyforum.org/index.cfm/amspolicyforum/), suggests
the need for more interdisciplinary communication between climate scientists and those
who study the efficacy of message communication. Dissonant science messages may
threaten in-group identity (Dixon, Hmielowski, & Ma, 2017), leading to resistance and a
greater distrust and negative affect toward scientists, and less support for action to
address climate change (Dixon & Huber, 2018; Nisbet et al., 2015). Targeted frames,
however, that emphasize free-market solutions have been found to increase acceptance of
climate science among conservatives (Campbell & Kay, 2014; Dixon et al., 2017).
We also find that there are circumstances under which skeptical audiences will be
more open to climate change policy information. Republicans who received an
environmental threat message sponsored by Republican Party leaders increased the
strength of their belief that climate change poses a threat to sustainable environment, their
support for laws to reduce greenhouse gas emissions, and their beliefs that a scientific
consensus exists regarding human activities being the primary cause of climate change.
Similarly, Republicans who received a national security threat message sponsored by
Republican Party leaders were less likely to state that climate change research is driven
by political considerations, and reported significantly lower perceptions that climate
change is a conspiracy or hoax. This clearly demonstrates the power that trusted in-group
(i.e., in-party leaders) sources could play in overcoming hurdles posed by partisan

polarization on climate change. On the other hand, we find that when the source of the
environmental threat message is Democratic Party leaders, Republicans become
significantly more likely to report that climate change research is driven by political
motivations and more likely to say that climate change is a hoax. The source of an
identical appeal thus has a powerful impact on how the information affects individuals’
beliefs not only about the threats that climate change presents and willingness to support
policy action, but also on broader perceptions about the motivations of climate change
research, and even beliefs that climate change is a hoax. This is a finding that should
prompt further exploration.
Future research should also explore the generalizability of our findings and the
impact of varied sources associated with climate change information across different
populations and using different content messages (e.g., highlighting the source of
information on scientific consensus reports or public health considerations). The results
we report are encouraging insofar as we show that sources perceived to be credible and
trusted and that deliver climate change messages to skeptical audiences can break through
the barriers that impede communication efforts.
This paper highlights the role that credible sources can play in shaping skeptical
audiences views about climate change and overcoming partisan barriers that impede
efforts to generate greater consensus among the U.S. public. The finding that Republican
Party leaders, and military leaders, had the strongest effect, on average, at enhancing the
framed messages suggests that source credibility may increase when an “unconventional”
position is taken by group leaders (Prior, Partridge, & Plant, 2014). The finding that
climate scientists had little effect, or at worst a negative effect, also needs further

attention. More exploration is necessary to understand the efficacy of source credibility
linked with distinct arguments on climate change as well as the duration and persistence
of efforts to overcome polarization and foster consensus and climate engagement.

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Table 1. Experimental Design and Predictions
Condition Treatment Predicted outcome
National
Security
(No source)
(N=184)
Some groups have recently argued that droughts and
flooding caused by climate change are a threat to the
security of the United States…
National Security
Baseline
Military
Leaders
(N=184)
A group of military leaders including generals and
homeland security officers have recently argued that
droughts and flooding caused by climate change are a
threat to the security of the United States…
H1: increase the
frame’s impact.
Democratic
Party Leaders
(N=178)
A group of Democratic leaders in the House and Senate
have recently argued that droughts and flooding caused
by climate change are a threat to the security of the
United States….
H3: increase
impact for Dems,
no effect on
Repubs.
Republican
Party Leaders
(N=183)
A group of Republican leaders in the House and Senate
have recently argued that droughts and flooding caused
by climate change are a threat to the security of the
United States…
H3: increase
impact for
Repubs., no effect
on Dems.
Climate
Scientists
(N=184)
A group of climate scientists have recently argued that
droughts and flooding caused by climate change are a
threat to the security of the United States…
No prediction
relative to
baseline.
Environment
(No source)
(N=192)
Some groups have recently argued that climate change
is a threat to the environment of the United States…
Environmental
Baseline
Military
Leaders
(N=187)
A group of military leaders including generals and
homeland security officers have recently argued that
climate change is a threat to the environment of the
United States…
No prediction
relative to
baseline.
Democratic
Party Leaders
(N=189)
A group of Democratic leaders in the House and Senate
have recently argued that climate change is a threat to
the environment of the United States.
H3: increase
impact for Dems,
no effect on
Repubs.
Republican
Party Leaders
(N=183)
A group of Republican leaders in the House and Senate
have recently argued that climate change is a threat to
the environment of the United States.
H3: increase
impact for
Repubs., no effect
on Dems.
Climate
Scientists
(N=184)
A group of climate scientists have recently argued that
climate change is a threat to the environment of the
United States.
H2: increase the
frame’s impact.

Figure 1. Message Source Effects Relative to No Source Appeal’s Baseline

Table 2: Main Effects (Democrats only)
National Security Frame
Threat Nat.
Sec.
(Model 1)
Threat
Env.
(Model 2)
Politically
Motivated
(Model 3)
Support
Laws
(Model 4)
Happening
(Model 5)
Scientific
Consensus
(Model 6)
Hoax
(Model 7)
Military Leaders 0.28*0.17 0.06 0.15 0.09 0.04 0.19
(0.18) (0.13) (0.25) (0.17) (0.15) (0.17) (0.24)
Democrat Leaders -0.21 0.18*-0.22 -0.07 0.02 -0.01 0.03
(0.19) (0.13) (0.25) (0.17) (0.15) (0.17) (0.24)
Republican Leaders -0.15 0.11 -0.36*0.14 0.16 0.06 -0.25
(0.18) (0.13) (0.25) (0.17) (0.15) (0.17) (0.24)
Climate Scientists 0.19 0.00 0.01 -0.18 -0.17 -0.24*0.13
(0.19) (0.14) (0.25) (0.17) (0.15) (0.17) (0.24)
Constant (No-Source Nat. Sec.) 3.33*** 4.38*** 2.41*** 6.43*** 6.47*** 6.31*** 1.84***
(0.12) (0.09) (0.17) (0.11) (0.10) (0.12) (0.16)
N392 392 392 392 392 392 391
Environmental Frame
Military Leaders 0.57*** 0.10 -0.49** 0.04 0.05 0.10 -0.04
(0.19) (0.12) (0.25) (0.16) (0.15) (0.16) (0.22)
Democrat Leaders 0.19 0.22** -0.19 -0.05 0.12 0.02 -0.11
(0.20) (0.13) (0.26) (0.17) (0.16) (0.17) (0.23)
Republican Leaders 0.21 0.09 -0.09 -0.13 -0.22*-0.02 0.23
(0.20) (0.12) (0.26) (0.16) (0.15) (0.17) (0.22)
Climate Scientists 0.06 0.16*0.01 -0.04 0.05 -0.23*0.06
(0.20) (0.12) (0.26) (0.16) (0.15) (0.17) (0.22)
Constant (No-Source Env.) 3.22*** 4.42*** 2.55*** 6.45*** 6.44*** 6.26*** 1.76***
(0.14) (0.09) (0.18) (0.11) (0.11) (0.12) (0.16)
N422 422 421 422 421 422 422
Note: Cell entries are OLS coefficient estimates, with standard errors in parentheses. Conditions receiving the national security frame are compared to the No-
Source National Security baseline; conditions receiving the environmental frame are compared to the No-Source Environmental condition. Asterisks represent
one-tailed p-values. * p < 0.10 ** p < 0.05 *** p < 0.01

Table 3: Main Effects (Republicans only)
National Security Frame
Threat Nat.
Sec.
(Model 1)
Threat
Env.
(Model 2)
Politically
Motivated
(Model 3)
Support
Laws
(Model 4)
Happening
(Model 5)
Scientific
Consensus
(Model 6)
Hoax
(Model 7)
Military Leaders 0.47** 0.01 -0.61** 0.13 -0.27 0.09 -0.61*
(0.23) (0.25) (0.37) (0.36) (0.35) (0.34) (0.38)
Democrat Leaders 0.19 -0.11 -0.50*0.20 -0.44*-0.06 -0.29
(0.22) (0.24) (0.35) (0.35) (0.34) (0.33) (0.37)
Republican Leaders 0.22 -0.01 -0.96*** 0.18 0.09 -0.01 -0.51*
(0.23) (0.25) (0.37) (0.37) (0.35) (0.35) (0.39)
Climate Scientists 0.12 -0.26 -0.23 -0.22 -0.32 0.05 -0.06
(0.21) (0.23) (0.34) (0.34) (0.33) (0.32) (0.36)
Constant (No-Source Nat. Sec.) 2.09*** 3.16*** 4.82*** 4.55*** 4.91*** 4.85*** 4.07***
(0.16) (0.17) (0.25) (0.25) (0.25) (0.24) (0.27)
N287 287 288 288 288 287 287
Environmental Frame
Military Leaders 0.13 0.17 0.38 0.16 0.02 0.02 0.54*
(0.26) (0.26) (0.38) (0.36) (0.35) (0.32) (0.38)
Democrat Leaders -0.21 -0.10 0.59*0.07 0.12 0.04 0.60**
(0.25) (0.25) (0.36) (0.34) (0.33) (0.30) (0.36)
Republican Leaders 0.18 0.50** -0.12 0.51*0.43 0.60** -0.16
(0.26) (0.26) (0.38) (0.36) (0.35) (0.31) (0.37)
Climate Scientists 0.09 0.05 0.44 0.11 0.06 0.54** 0.43
(0.25) (0.26) (0.37) (0.35) (0.34) (0.31) (0.37)
Constant (No-Source Env.) 2.48*** 3.08*** 4.24*** 4.76*** 4.80*** 4.82*** 3.52***
(0.18) (0.19) (0.27) (0.26) (0.25) (0.22) (0.27)
N274 274 271 273 273 274 273
Note: Cell entries are OLS coefficient estimates, with standard errors in parentheses. Conditions receiving the national security frame are compared to the No-
Source National Security baseline; conditions receiving the environmental frame are compared to the No-Source Environmental condition. Asterisks represent
one-tailed p-values. * p < 0.10 ** p < 0.05 *** p < 01.