1. Introduction

With the development of economy and industries, various environmental problems have emerged. Environmental issues and protection have become heated topics and attracted public attention. How to protect the environment and achieve the goal of creating a sustainable and green global society is considered crucial and necessary for the whole human race. The need for sustainable consumption has been recognized by a majority of countries worldwide. The United Nations set forward Sustainable Development Goals (SDGs) in 2015. SDG 12, Responsible Consumption and Production, aims to ensure sustainable consumption and production patterns in the global development [1]. It highlights the importance to achieve sustainable consumption.

In the field of consumer behavior, plenty of prior scholars had their studies focused on researching why individuals choose to purchase a particular sustainable product that is designed to be more eco-friendly or choose to behave more environmental friendly when consuming. Prior scholars segmented various factors affecting sustainable and green consumer behavior, including governmental factor, personal factors and social factors.

This paper will review studies that researched factors of sustainable consumer behavior (SCB) and green consumer behavior (GCB). This paper concludes and divides factors into external and internal factors. Each category includes one or two main studied factors that have been commonly researched by prior scholars. Four studies will be respectively introduced as an example study from aspects of research design and methodology as well as research results. Each study will be discussed critically, so as to serve the main goal of concluding the current research findings and giving suggestions on how future studies should be conducted in the field of consumer behavior. Furthermore, suggestions on government, marketers and schools will be given at the end of this paper based on the concluded research findings.

2. Introduction to the Key Concepts

There are several key concepts that require clarification and elaboration for this paper, including SCB/GCB, social norms so as environmental cognition and knowledge.

2.1. Sustainable/Green Consumer Behavior

SCB is behavior that when people are choosing products to purchase, they try to purchase the one that can simultaneously meet their personal needs and have limited non-eco-friendly impacts [2,3]. SCB is considered to be balancing three core aspects, economical, social and environmental desire for future generations and the whole human race [4].

GCB is behavior that people take environmental and social concerns into account during their either purchase or non-purchase decision-making journey [5].

There are slight differences between the definition of SCB and GCB. However, they are all behaviors that show people’s tendency to achieve individual accomplishments in terms of environmental protection.

2.2. Social Norms

Norms are intrinsic rules or common beliefs that can decide the social expectation of an individual’s behavior. Social norms can influence an individual’s final decision, by defining what seem to be regular or usual to be done in the society [6]. Social norms can be referred to as implied social standards that people may choose to meet with. What needs to be noted is that social norms can be described and can vary in a time period. Descriptive norms usually indicate what most people choose to do in a specific condition [7].

2.3. Environmental Cognition and Knowledge

Environmental cognition is the process of how people from all age groups perceive and approach the natural surroundings [8]. Environmental cognition also embodies how people collect, sort and memorize the natural environment [9].

Environmental knowledge is information that can be used in people’s decision-making process. Used information is selected by its practicality, consistency with present rules or significance in terms of the field called Earth and Planetary Sciences [10]. This concept is defined as a crucial precursor symbolizing and resulting in behaviors that can be beneficial to the environment.

3. The Effect of Social Norms (External)

There are several external factors that may influence SCB and GCB researched by previous research groups, including the effect of government policies and even the influence of world-wide pandemics [11]. Among all the factors previous scholars have shown interest in, the effect of social norms has been frequently researched. In the following content, some examples of the previous studies will be concluded and reviewed.

3.1. Basic Literature Review on Previous Studies

In the prior studies with the common goal of studying the effect of social norms, different research aims, assumptions and related methods were investigated.

There were research groups who focus on studying the effectiveness of differently segmented types of social norms. In research conducted by Ryoo et al., social descriptive norms were segmented into provincial and general norms which could be moderated by a certain level of how the norms were explained [7]. In research conducted by White et al., various studied aspects were shown under the framework of SHIFT-Social influence, Habit formation, Individual self, Feelings and cognition and Tangibility-so as to study more about how people can be “shifted” into buying sustainable products. [12].

There were groups who concentrated on the effect of peers, also quite known as the effect of herd behavior. Having provided with the different information of peers’ decision on sustainable products, people’s willingness toward purchase varied with each other [13,14].

There were also diverse research methods applied by respective research groups, including questionnaires, laboratory experiments as well as field experiments. Examples of previous studies will be given in detail in following reviews on example researches and concluded in 3.4. Comparisons among Previous Studies.

3.2. Detailed Review on the Effect of Descriptive Norms and Construal-Level on Consumers’ Sustainable Behaviors

In this part, research completed by Ryoo et al. will be reviewed in detail as an example research [7].

3.2.1. Research Design and Methodology

This research was designed to testify the assumption of the effect of provincial norms and general norms and to clarify whether they can be influenced by a particular moderator, construal-level. High level messages are normally abstract, while low level ones are more detailed and concrete [7]. The research includes 2 different studies in total.

In study 1, an experiment was carried out, in which the subjects were asked to imagine being at a coffee shop and deciding whether to use a store-owned mug for sustainability or buy a less eco-friendly cup through a designed advertisement. Provincial norms were presented to the subjects by giving the information that the coffee shop was located in a popular district in South Korea, while the presented general norms were less specific about the location. The mediator of construal-level messages changed between groups, for example, by simply noting the responsibility of environmental protection or specifying the process of buying the coffee. However, both norms were shown under the same hypothetical condition that 75% of the customers who visited the coffee shop tended to choose the mug.

There were altogether 82 female and 66 male participants with the average age of 32.48. They finished a questionnaire on their willingness to participate in the mug campaign and their belief extents on the norm using a 7-point Likert type scale.

In study 2, a field experiment was conducted with the same method in study 1, except that the experimented coffee shop exists in real life and the experiment lasted for 5 weeks. Staff members recorded the number of people choosing for a mug after reading the designed advertisement.

3.2.2. Research Results

In study 1, the data were analyzed and the research group found that both provincial norms or general norms as social norms can be a strong conviction of purchasing. Plus, the mediator, construal-level can also be effective impact on people’s willingness to consume sustainably. But provincial norms can lead to a higher compulsion of people’s sustainable gesture only when they are presented with specific consumption steps of how to use or purchase a mug in the coffee shop, for example, to firstly tell the staff that they would like to use a mug.

In study 2, the recorded data showed that a total 5.17% of all the customers from both subject groups choose to consume sustainably. And the test result turned out to remain consistent with those in study 1.

3.2.3. Discussion

This research was completed thoroughly by carrying out both a laboratory and field experiment. The hypothesis of the research group was confirmed and the influence of the mediator was clearly indicated. Additionally, the research group considered the processing fluency of the participants. The research hypothesis and results were confirmed in both experiments, which improved the eco-validity of this research. However, there were limitations and insufficiency in the research. For example, there could be possible undetected errors of staffs in the field experiment and potential bias of the consumers visiting the coffee shop.

3.3. Detailed Review on Disentangling Social Normative Influences on SCB

In this part, another research completed by Pristl et al. will be reviewed in detail as an example research [15].

3.3.1. Research Design and Methodology

This research was designed to analyze the mechanisms of the social normative influence. It includes altogether 2 studies.

In study 1, an online experiment was conducted in a university in Germany. 306 student with the middle age of 25.35 participated, 45.8% of which are female. The participants were initially measured in terms of self-efficacy and self-concept. They were then requested to rate a variety of goods that are common for young people based on the quality, sustainability of the product and their desire for this good. The goods were all considered as non-eco-friendly. The participants were lastly asked to rate their personal norms, perceived social norms in consideration of consuming decisions in terms of sustainability based on the product information. After data collection, SPSS PROCESS v3.4 (Hayes, 2018, model 4) was used to generate the connections between different variables.

In study 2, the research group further studied the mechanism of how social norms can influence the SCB in terms of sender-specific, recipient-specific context factors, gender and pro-sustainability world view. Another online experiment participated by students from a university in Germany was conducted. The database consisted of 106 participants with the average age of 26.22, 52.4% of which were female. They were asked to think of a person depending on different given conditions, who would later be playing the role of a communicator of a statement of social norms. This person could be a close relative or a distant role-model, such as role models in sports, stars or actors. Then hypothetically, they were faced with the situation where they were considering buying a pair of sustainable shoes. The participants were randomly assigned in different groups with respective conditions, where they were instructed to think of their close or distant communicators. Also, the descriptive condition group were given hypothetical background information that there were many students purchasing sustainable shoes to measure the influence of descriptive norms. Lastly, they rated their purchase wills toward the pair of shoes.

3.3.2. Research Results

In study 1, purchase intentions of whether to buy non-eco-friendly goods were confirmed to have a positive correlation with the extent of perceived social norms and could be influenced by people’s personal norms.

In study 2, the research group found that by having a distant reference person as a communicator, such as celebrities, the purchase intention is more likely to be influenced by descriptive norms. The research groups also demonstrated the existence of gender differences. Compared with male, female are more likely to purchase the product when given descriptive norms. Additionally, there were not significant correlation between pro-sustainability world outlook, social norms and purchase intention.

3.3.3. Discussion

This research evaluated the relationship between purchase intention and social norms where personal norms serves as a mediator, as well as the one between social (descriptive) norms and purchase intentions when considering various potential variables. This research was detailed and it explained how social norms function to impact SCB. However, there were also limitations of the research. For instance, study 2 was rather lack of samples, which may result in the inaccuracy of the result and the hypothesis. Also, both studies were all laboratory and may differentiate from the real life conditions. The subjects in the laboratory research were asked to think of a person as a communicator. The impacts and behaviors of the imagined persons could be different from those in reality.

3.4. Comparisons among Previous Studies

3.4.1. Similarities

When previous studies are compared with each other, a few similarities can be summarized:

For research method, in researching the effect of social norms on SCB and their correlations, prior scholars chose to conduct either an experiment or questionnaire. In Ryoo’s study and Pristl’s study that were mentioned in the previous paragraphs, research groups used the combination of experiment and questionnaire. By conducting an experiment in the first place and then collecting questionnaire samples, final test results were found. There were a few other research groups who chose to apply a single research method to complete a quantitative research.

For research findings, in previous studies, similar research findings were revealed that social norms can have positive influence on SCB mediated by different variables, by having a positive correlation with the purchase intention of sustainable goods. The effect can be slightly different among people with different genders, role models and personal norms.

3.4.2. Differences

For research perspectives, different research groups performed their studies from different perspectives. The effect of social norms were analyzed by assuming different mediators that may influence the result and by segmenting social norms into descriptive or injunctive norms.

For research subjects, different research groups conducted the research in different regions. Ryoo’s study was conducted in South Korea, while Pristl’s study and research conducted by Gideon Fadiran and Stephen Onakuse were conducted in European countries [13]. This may lead to slightly different test results due to personal cultural backgrounds.

3.5. Summaries

In previous studies reviewed in this section about the effect of external factor, social norms, on SCB, a majority of experiments and questionnaires were employed. Given this research situation, SCB and GCB are better analyzed and elaborated to serve the purpose of shifting consumers purchase intention and promote sustainability. Different research groups came to the conclusion that SCB can be shifted by social norms, especially under the condition that descriptive norms are introduced, so that herd behavior or social learning can play a great role in the correlation. However, it is suggested that more studies be continuously carried out because of the fickleness of social norms in different cultures and that more participants take part in the research. It should also be clarified that research results may differentiate from people’s actual behaviors.

4. The Effect of Environmental Cognition and Knowledge (Internal)

4.1. Basic Literature Review on Previous Studies

Among previous studies on the effect of environmental cognition so as environmental knowledge, scholars focused on several mediators and how exactly environmental knowledge can influence SCB and GCB.

By designing surveys based on theoretical models and conducting interviews, scholars claimed that environmental knowledge could influence environmental concern, which would then have an impact on SCB and GCB. Researchers found that this effect was rather positive [16]. Some researchers also suggested that environmental concern could be a mediator for purchase intention. Moreover, how people perceive and are aware of the importance of environment can influence consumers’ purchase intentions, by subtly enhancing the purchase intention in terms of changing attitudes and subjective normative cognition [17,18].

4.2. Detailed Review on the Impact of Environmental Cognition on GCB

In this part, research conducted by Xie et al. will be thoroughly reviewed as an example research [18].

4.2.1. Research Design and Methodology

This research was worked on how environmental cognition could influence GCB, as well as green consumption subjective norms. In this research, the theory of planned behavior (TPB) was applied, in which consumption attitudes, subjective norms and perceived behavioral control were three critical variables. The research group assumed that environmental cognition could influence people’s attitudes toward consumption, subjective norms as well as perceived behavioral control.

This study used data from the 2010 China General Social Survey (CGSS2010). Apart from the invalid survey results, data of 3240 respondents from 31 provinces in China were considered the subjects for this research analysis. The data sample consisted of most provinces in China, which can be considered representative for a universal test result. All variables in the study were divided into two categories: individual-level variables and provincial-level variables. The former one includes controlled variables such as age, gender and educational level. The latter one includes controlled variables such as economic level and environmental quality. Consumption attitudes were measured on the Chinese version of the environmental concern scale. Higher scores represented stronger concerns for the environment and more positive attitudes toward GCB. 3 claims were used to survey the subjective norms. Higher scores stood for profounder influence of norms on GCB. Other 6 questions were asked to judge the perceived behavioral control. Higher scores unfolded one’s more participation in green consumption. In order to measure the level of people’s environmental cognition, there are 10 statements in CGSS2010 particularly. Higher scores represented a better knowledge of the environment.

4.2.2. Research Results

The results suggested that a more comprehensive environmental cognition could result in a more positive attitude towards green consumption, stronger green consumption subjective norms and easier perceived GCB. Also, evidence showed that environmental cognition could have a stronger effect when individual variables as gender, age and educational level were controlled. While environmental cognition can have positive impact on 3 tested variables, these variables with high scores can also lead to stronger environmental cognition. It was also implied that there could be differences between regions in terms of the influences of environmental cognition. In eastern regions in China, the influence of environmental cognition on attitudes toward GCB is stronger than in central and western regions.

4.2.3. Discussion

This study analyzed the impact of environmental cognition on GCB from different perspectives. A large sample pool was applied. Various hypothesis in this research were proved to be correct and a reciprocal relationship between environmental cognition and the variables was revealed. However, this research used outdated data from 2010, which may result in the deviation and the limited accuracy of test results over time. The research group indicated that due to the enormous impact of COVID-19 pandemic, the data from 2010 might be time-limited [18]. Furthermore, the Chinese government has enhanced the publicity of environmental protection since 2010. The environmental cognition of the individuals might have changed along with time change.

4.3. Detailed Review on the Impact of Environmental Knowledge on Environmental Concern and Intention of SCB

In this part, a study completed by Saari et al. will be reviewed in detail as an example research [19].

4.3.1. Research Design and Methodology

This study aimed to reveal the relationship between environmental knowledge/risk perception and environmental concern and how the concern can influence SCB.

This research was conducted by using items in reflective measurement models, in which gender, age, degree and countries were controlled variables. The research data were selected from a data set collected between 2009 and 2013 by the International Social Survey Programme. The data were collected by questionnaires, interviews and mixed-methods. The responses were from 36 different European countries. 11675 responses were used to analyze, among which there were incomplete data that were treated with expectation-maximization method. In the model, various measurement items were divided into 5 categories in relation with environmental knowledge, environmental risk perception, environmental concern, behavioral intention and SCB.

During the analysis, PLS-SEM model was utilized to study complicated mediation effects.

4.3.2. Research Results

With the confounding variables, namely, age, gender and education being controlled for, this research indicated that both environmental knowledge and risk perception can influence environmental concern. In terms of SCB, environmental knowledge has a greater direct impact, while it can also influence the behavior by firstly mediating behavioral intention. The positive effect of environmental knowledge is in line with prior studies.

4.3.3. Discussion

This research concentrated on analyzing the two main factors, environmental knowledge and risk perception. The research group investigated on this topic, so as to serve the purpose of enlightening and giving suggestions on policy makers and education about the environment, which could be influential and meaningful to the European society. The approach by introducing the model of PLS-SEM in this research is considered cutting-edge and innovative in studying the two factors. However, there are limitations. Although non-related factors as gender or age had been controlled, there could still be biases among different countries that might result in the inconsistency of the result. Similar to the last research conducted by Xie et al., the data were also relatively out-dated and the incompletion of the data could lead to inaccuracy of the result.

4.4. Comparisons among Previous Studies

4.4.1. Similarities

When studies of prior scholars are compared with one another, a few similarities can be summarized:

For research subjects, in previous studies, research groups normally adopted quantitative research methods for further data analysis. For instance, in Xie’s study and study conducted by Liang et al., information collected from a large data base were obtained by designed questionnaires. Nevertheless, there were research groups who used mixed methods and employed data collected by interviews such as Saari’s study.

For research findings, after completing the data analysis, different research groups discovered similar results of the relationship between different factors. It was indicated that environmental knowledge can influence the behavioral intention of GCB and SCB. Also, environmental cognition can both influence or be influenced by individual’s attitude toward GCB. However, the extent of the relationships can vary form different regions and countries [18,19].

4.4.2. Differences

During research of how environmental cognition and knowledge can impact GCB and SCB, prior scholars all focused on various variables that need to be controlled or evaluated. Researchers performed their research from respective angles.

For research regions, research groups conducted their studies in different regions. In Saari’s study and Dimitrova’s study, all data were collected in European countries. Xie’s study and Liang’s study were conducted in China. This may result in minor differences of how specifically SCB and GCB can be influenced due to different political and cultural backgrounds.

For research models/softwares, prior researchers used different models or softwares to analyze the data. In Dimitrova’s study and Saari’s study, PLS-SEM was introduced and adopted. Whereas both SPSS software and PLS model were used for analysis in Liang’s study. Also, researches conducted by Liang et al. and Xie et al. were all based on TPB, while there were other groups who didn’t choose to apply a theory.

For research perspectives, different research perspectives and variables were considered in previous studies. Variables as age, gender, financial income were measured or controlled. There was research group who chose age as a variable, instead of controlling it. Moreover, the research group indicated that how age moderates the correlation between sustainable consumption behavior and SCB can also play a crucial factor [16]. Besides, different factors as environmental influences, attitude towards GCB or SCB and the promotion of sustainable consumption were examined in different researches.

4.5. Summaries

In previously reviewed studies about the effect of environmental knowledge and cognition, a good number of questionnaires and a few interviews were performed. The correlation between environmental knowledge, environmental cognition and SCB/GCB were discovered. Environmental knowledge can serve as a mediator of behavioral intention which will influence the consumer behavior. Environmental cognition can influence one’s attitude towards SCB and GCB, which leads to the behavioral change in consumption. The researches delivered clear analysis from various aspects, allowing the society to recognize the effect of environmental cognition and knowledge in sustainable consuming. Nevertheless, more researches could be carried out to further study the specific impact of individual variables as age, financial status and cultural background, so as to help government introduce specific policies and improve environmental education.

5. Discussion and Suggestion

5.1. Discussion

In this paper, various studies on factors influencing SCB and GCB were reviewed and concluded. It can be summed that both external and internal factors can be decisive in terms of affecting SCB and GCB. External factor, namely social norms can effectively influence people’s purchase intention and their consumption behaviors due to social learning. Internal factor, namely environmental knowledge and cognition can also play a crucial factor. By conducting questionnaires and analyzing the collected data, it has been revealed that environmental knowledge can mediated the relationship between behavioral intention and SCB/GCB. Moreover, environmental cognition can influence people’s attitude towards SCB/GCB. Therefore, all these factors can be related to the change of SCB and GCB. It can be implied that the change of SCB and GCB is often a result of external and internal factors being effective simultaneously.

5.2. Suggestion and Enlightenment

Based on the current results from different studies, several suggestions on pursuing sustainability and shaping SCB/GCB can be made:

Social norms can be susceptible to time change and can reflect the change of people’s common belief. Thus, government can play a crucial role in terms of developing sustainably by making related policies or propagandizing the importance of sustainable development and environmental protection. This can cultivate social and public awareness, as well as individual’s environmental knowledge. Hence, it can be helpful to encourage people to purchase sustainable and green products by forming social norms and increasing individual’s environmental cognition. Schools should also educate more about environmental protection and help increase students’ environmental knowledge.

For marketers who aim to attract potential consumers to purchase the company’s green products, they can try to improve the promotion tactics by presenting the sustainable advantages of the product that may meet the needs of potential consumers with environmental awareness. Besides, the company can invite famous spokespersons who serve as distant communicators. Also, the company can present former purchase data of their sustainable products in their advertisements to form descriptive norms, showing potential customers what most people have decided to do.

Therefore, it can be demonstrated that different social roles can be critical in developing a greener society and encouraging people to purchase green products.

6. Conclusion

This paper aims to review and discuss studies conducted by prior scholars based on the topic of factors affecting SCB and GCB. By reviewing former studies, how future scholars could conduct their studies and to what extent they could delve in the research field is concluded and suggested in this paper.

It is summed that both external and internal factors can have important influences. Social norms can affect SCB and GCB through social learning. Individual level of environmental knowledge and cognition can also impact SCB and GCB by increasing the purchase intention of an individual.

It is preferable that more studies should be conducted along with time change, since social norms may vary in a short time period. Moreover, more studies on the influence of environmental knowledge and cognition should be performed in various regions to prove the validity and consistency of the test results because of the possible cultural differences and economic development levels. Also, more factors could be discussed and researched in the future.

Based on the former research findings, it is suggested that different social roles, namely government, marketers and schools should contribute more to lead to sustainable development and green consumption.