Existing studies have demonstrated the importance of using digital media platforms, such as social media, in communicating environmental protection messages. Burksiene and Dvorak ^[1][3] did a comprehensive review of the literature about how environmental NGOs (ENGOs) used online media platforms. The researchers found that social media plays a crucial role in disseminating environmental information. Di Tullio and colleagues ^[2][4] reported in the study that social media are beneficial for environmental activists or organizations to engage and educate the audiences of a message about sustainability through interactive, two-way communication. Jönsson et al. ^[3][5] believed that social media are more effective and efficient channels to communicate pro-social messages (e.g., environmental protection) than legacy media platforms. Thus, the current research focuses on examining environmental communication strategies that can be applied in conducting pro-environment social media campaigns. Communication strategies are defined as a plan of action that can be used by message senders on social media to achieve communication goals such as increasing message exposure or improving message persuasiveness ^[4][6]. The specific strategies investigated in the current study are (1) communicating the message with the help of different types of sources; (2) framing messages positively or negatively; and (3) manipulating messages that receive either low or high levels of support from the public.

A challenge that environmental advocates and their communication campaigns face is to entice and engage potential target audiences. To many people, educational information about environmental protection seems uninteresting. Fortunately, there are various ways that environmental advocates (or organizations) can employ to entice and engage audiences. One of the simple techniques is employing an entertaining figure, such as a celebrity, to serve as a spokesperson (or a source) for the communicated information. The goal of using such a figure is to utilize a celebrity’s charismatic image with the hope that audiences may unconsciously associate the image with the message posted by the celebrity. Empirical studies have shown the success of using celebrities as campaign ambassadors in brand-consumer communication ^[5][6][7,8]. However, the efficacy of the practice in the context of environmental communication is debatable ^[7][9]. Thus, the main goal of the current research is to empirically ascertain the effectiveness of employing celebrities as a source of information in environmental communication campaigns on social media.

In addition to the use of celebrity, two potential cues on social media may instantly attract audiences’ attention: the framing of a message and the overall support a message receives. Social media are unique in that audiences can discern how others think of a post by observing the popularity metrics such as likes, shares, and comments. The metrics, similar to message framing, can be manipulated to the advantage of the message sender. Thus, another goal of the study is to examine how the framing of a message (i.e., message valence) and the level of support a message receives (i.e., bandwagon support) affect environmental communication effectiveness on social media.

Four online experiments were conducted. In the experiments, a series of mock social media campaign messages were created. Undergraduate college students were sampled in the experiments. Young adults are more likely to adopt a novel idea since they are still at an early stage of life with their worldview forming, and such a worldview formed in the early ages may serve as an anchor to guide their later life decisions ^[8][10].

2. The Perceived Bandwagon Support

Empirical evidence shows that people are easily influenced by others’ opinions or behaviors ^[9][10][24,25]. Scholars have proposed a few constructs that are, in essence, depicting social influence in the digital realm. One of the constructs is the perceived bandwagon support ^[11][26]. The perceived bandwagon support represents an individual’s perception of how much support (or disapproval) a digital entity receives from fellow users. For instance, a product review score reveals a product’s popularity, and consumers, who have never bought the product, can utilize the review score to help them infer product quality and make purchase decisions.

3. The Impact of Message Framing

The main, introductory text of a social media post is a person’s first contact with the issue portrayed in the post. The overall tone (i.e., valence) of the message is important. since it affects an individual’s general impression of the perceived information ^[12][27]. Thus, another focus of the current research is to examine how the valence of a social media message affects audiences. According to the negativity bias literature, the negatively framed message may be seen as more important in the eyes of audiences. The negativity bias is a psychological phenomenon that which negative events are regarded as more significant or more salient than positive ones ^[13][14][28,29]. The cause of the bias is either due to theour loss-aversion mentality or the scarcity of the occurrence of negative events in comparison to positive ones ^[15][16][30,31]. Thus, it is reasonable to deduce that a social media post that discusses the damage or loss caused by an environmental issue may seem more astounding in the eyes of audiences than a post that discusses the same issue in a positive light (e.g., the benefits of environmental protection).

4. Source of Information

Celebrities have been employed by many marketers to improve the efficiency of brand-consumer communication especially when the brand or marketer is communicating with younger audiences ^[17][32]. Celebrity endorsement has been discussed by existing studies from various angles ^[18][19][33,34]. Some studies demonstrated the benefits of using celebrity spokesperson in marketing activities ^[5][6][20][7,8,35], while a recent study conducted by Olmedo et al. ^[7][9] cast serious doubt on the overall effectiveness of celebrity endorsers in promoting environmental causes. Olmedo and colleagues analyzed 79 celebrity-involved environmental campaigns and 15 academic studies about the topic. Three key findings were summarized. First, most campaigns that utilized celebrity spokespersons were conducted in China. Second, few, if any, studies have examined how attributes of celebrity—a widely examined perspective in the marketing literature—affected green advertising effectiveness. Third, and most importantly, the study revealed that none of the campaign objectives were measurable. The lack of measurable objectives renders it impossible to determine whether the claimed campaign outcomes are a result of celebrity involvement. It is unclear how many, or if any, marketing agencies and environmental protection organizations have employed empirical research methods to evaluate the impact of celebrity involvement in a social media environmental communication campaign. Thus, the main goal of the current study is to empirically ascertain if a celebrity, as the source of information, is more effective in disseminating environmental campaign messages than a regular source of environmental information such as the U.S. Environmental Protection Agency (EPA). Source-related information reminds an individual to recall an experience, impression, or memory related to the source, and the individual associates the impression with their evaluation of the current encounter such as a tweet about climate change ^[21][22][23][14,36,37]. One of the impressions associated with the source is whether the source is credible. Source credibility is chosen as the conceptual foundation to differentiate the types of sources manipulated in the current research because the construct is likely to affect behavioral intention and believability of information ^[24][38].