Pro-environmental behavior (PEB) has long been considered a moral issue [
1,
2] and it has been referred to in many different ways in psychological literature, including “environmentally-concerned behavior” [
3], “environmentally significant behavior” [
4], “environmentally responsible behavior” [
5], “ecological behavior” [
6,
7], and “sustainable behavior” [
8,
9]. Overall, there is wide agreement across the above terms that PEB implies friendly actions towards the environment, resulting in the protection of its well-being. From a psychological perspective, Stern [
4] convincingly discussed the difference between the impact-oriented and the intent-oriented approach in understanding PEB. The first has to do with the consequences of human action on the environment (e.g., car use and environmental pollution); the second implies the role of human intentions behind the behavior, namely what impacts people expect to have on the environment through willing actions (e.g., avoiding buying plastic products). The author has stressed that “environmental intent may fail to result in environmental impact” (p. 408); it is thus essential to identify target behaviors, whose impacts on the environment can be huge, and then adopt an intent-oriented approach to understand the psychological determinants of those conducts.
Another key issue has to do with the measurement of PEB. In this regard, Lange and Dewitte [
29] recently debated the existing measures, how they have been applied, their strengths and weaknesses, and potential for improvement. A relevant distinction was made between behavioral tasks to be used in an experimental setting, self-reports, and observations in ecological conditions. Beyond the role of biases and ecological validity, the choice between them depends on several aspects, including the broader vs. narrower focus of PEB under investigation. Although the prediction of actual behavior through self-reports should take into account a variety of relevant moderators [
30], the authors have pointed out that when different PEBs and their psychological determinants have to be investigated, the use of self-reports can be highly recommended. Going further in this reflection, Lange and Dewitte [
29] stressed the importance of using multi-item validated scales vs. single-item measures to better “contributing to a cumulative science of PEB” (p. 93). Among the multi-item scales developed over time, the authors identified 20 validated tools for the measurement of PEB in general, encompassing different dimensions—or domains—of PEB. With reference to the adult population, Karp [
31] developed the environmental behavior scale (16 items), investigating activism, good citizenship, and healthy consumption; Stern, Diez, Abel, Guagnano, and Kalof [
32] used the environmentalism scale (16 items), addressing committed activism and three dimensions of support for the environmental movement, namely consumer behavior, willingness to sacrifice, and environmental citizenship; through several studies, Kaiser and colleagues [
33,
34,
35] developed, validated, and refined the general ecological behavior scale (40 items in the shorter version), measuring energy and water conservation, mobility and transportation, waste avoidance, recycling, consumerism, and vicarious behaviors toward conservation. In a cross-cultural research, Schultz et al. [
36] administered the environmental behavior scale (12 items), referring to a variety of different PEBs included in a single dimension. Markle [
37] developed the pro-environmental behavior scale (19 items), with four dimensions, labelled conservation, environmental citizenship, food, and transportation. In a quali–quantitative study among landowners, hunters, and birdwatchers, Larson, Stedman, Cooper, and Decker [
38] validated the pro-environmental behavior scale (13 items), with the four dimensions of conservation lifestyle behaviors, land stewardship behaviors, social environmentalism, and environmental citizenship behaviors. Lange and Dewitte [
29] argued that “based on its frequency of use and thoroughness of psychometric evaluation, the General Ecological Behavior (GEB) measure can probably be considered the best established of these domain-general propensity measures” (p. 94).
1.1. Values and Other Psychosocial Determinants of Pro-Environmental Behavior
The roles of human behavior in environmental problems, such as pollution [
39,
40,
41,
42,
43], waste of resources [
44], loss of biodiversity [
45,
46,
47], and overall climate change [
48], have been extensively documented. Thus, it is fundamental to understand the psychological determinants of those PEBs whose impacts on the above environmental problems can be more pronounced [
49]. In this regard, Steg and Vlek [
50] proposed an integrative framework on pro-environmental motivation and behavior, suggesting a link between the identification of PEBs that significantly affect environmental quality, relevant psychosocial determinants, interventions, and evaluation of efficacy. The authors have distinguished between three motivational factors towards PEBs, namely moral and normative concerns, costs and benefits, and affect.
Both moral and normative concerns and cost/benefit weighting have to do with cognitions; that is, what people think about PEBs, the evaluated importance and consequences in personal or social terms. Within this domain of psychosocial determinants of PEBs, the literature has identified several relevant constructs. Personal values have been defined as the beliefs on desirable and trans-situational goals, with different importance, acting as guiding principles in people’s lives [
51]. The universal structure of human values has been consistently shown [
52,
53,
54] and, according to the value attitude behavior model [
55], values are at the base of a cognitive hierarchical mechanism leading to behavior that influences attitudes and norms through a ‘value orientation’. Specifically, the role of personal values in PEBs has been found in a variety of empirical studies. For example, Schultz and Zelezny [
56] showed that personal values referring to self-transcendence are important predictors of PEBs across five countries. In Brown and Kasser’s study [
57], a positive relationship between altruistic values and PEBs emerged. Nordlund and Garvill [
58] found a relationship among self-transcendence, environmental values, personal norms, and PEBs. In a cross-national study across 27 countries, Oreg and Katz-Gerro [
59] outlined an indirect relationship between post-materialistic values [
60] and PEBs. Kaiser, Ranney, Hartig, and Bowler [
61], with specific reference to values related to the environment, predicted pro-environmental intentions, which in turn predicted PEBs in two studies involving different social groups in the Swiss and in the US. deGroot and Steg [
62] found empirical evidence of a relevant distinction among egoistic, altruistic, and biospheric values for understanding environmental beliefs, intentions, and PEBs, with biospheric values explaining best the pro-environmental cognitive and behavioral dependent variables. deGroot and Steg [
63] also argued how altruistic and biospheric values can be considered as more stable predictors of PEBs, but also egoistic values can be compatible with pro-environmental issues, especially when the perceived conflict between them is reduced. Moreover, Nguyen, Lobo and Greenland [
64] found a positive effect of biospheric values on purchasing behavior of energy efficient appliances. The role of values has also been consistently supported with reference to more committed PEBs, such as environmental activism [
65,
66,
67,
68].
Recently, a few studies have extended the attention to family values in relation to environmentally-related behaviors. From the national survey carried out by Oh et al. [
69] involving 1519 respondents (18 years and above) in Singapore, it has emerged that biospheric (e.g., protection of the environment) and altruistic (e.g., helpful) family values—measured by asking “How important are the following principles in your family?”—were directly and positively related to a connection to nature and experiences of nature (i.e., the frequency and duration of urban greenspace and private or community garden use), while egoistic (e.g., social power) family values had a direct but negative association. The relationship between biospheric values and the connection to nature was also significantly mediated through social norms of family and friends, and personal experiences of nature.
Environmental concern has also been taken into account when explaining PEBs. Environmental concern has been conceived as an attitude towards facts and behaviors with negative consequences for the environment [
70]. The most frequently used psychometric tool for the measurement of environmental concern is the new ecological paradigm scale (NEP) [
71,
72], referring to humans’ ability to upset the balance of nature, the existence of limits to growth, and humans’ right to rule over nature. More recently, Corral-Verdugo, Carrus, Bonnes, Moser, and Sinha [
73] proposed a different tool, the new human interdependence paradigm scale (NHIP), suggesting and measuring an integrative vs. dichotomic vision of human needs and nature conservation. Environmental concern has emerged as a relevant construct in predicting PEBs in several studies [
74,
75,
76,
77]. However, the relationship between environmental concern and PEBs is usually not strong, because of the moderation or mediation effect of other variables. To give an example of the former, in a study involving respondents from 32 countries, Tam and Chan [
78] found a role of cultural barriers in the association between environmental concern and PEBs, so that the size of this association varies across nations. Gifford and Nilsson [
79] recently proposed a review on these variables. Norms have been frequently investigated as examples of the latter, and are included in comprehensive theories, such as the Norm Activation Model (NAM) [
80], and the Value-Belief-Norm Theory (VBN) [
32]. Within these frameworks, personal norms have emerged as the ultimate, and more direct determinants of PEBs in a causal chain, with consistent empirical evidence [
63,
81,
82,
83,
84]. Subjective norms, referring to the expectations of significant others, have been considered as well in the Theory of Reasoned Action (TRA) [
85] and its extension, the Theory of Planned Behavior (TPB) [
86]. These theories best represent the costs/benefit analysis in psychological terms proposed by Steg and Vlek [
50]. The predictive power of these theories on PEBs, also in association with VBN variables, has been repeatedly shown [
7,
59,
87,
88,
89,
90]. Moreover, the influence of norms on PEBs has been further investigated with reference to a distinction between several constructs, such as injunctive and descriptive norms [
91,
92,
93,
94], or local norms [
95,
96]. Farrow, Grolleau, and Ibanez [
97] recently provided a review of different conceptualizations and empirical evidence on the effectiveness of social norms on PEBs.
Finally, Steg and Vlek [
50] explored a role for affective processes, with the case of car use as the first PEB considered in empirical investigation. In this regard, Nilsson and Küller [
98] showed a negative relationship between car affection and the acceptance of policy measures to reduce car use. Steg [
99] found a stronger importance of symbolic and affective vs. instrumental motives for car use among commuters. In Carrus, Passafaro, and Bonnes’s study [
100], a significant effect of anticipated negative emotions (e.g., feeling angry, frustrated, unsatisfied, discontented, guilty, sad) in reducing the use of private cars has also emerged. Moons and De Pelsmacker [
101] reported on a significant role of emotions in the use of electric cars among Belgian drivers, even though peculiarities for different consumer segments.
Based on recent literature, this framework has possibilities for further developments. First, identity referring to a specific PEB has emerged as an added variable, improving the predictive power of different models, including TPB. This was shown in several studies analyzing recycling [
102], ecological consumption [
103,
104], water or energy conservation [
105,
106,
107], and activism [
108]. More interestingly, the influence of a general environmental identity in PEBs has been proposed, referring to the aspect of one’s self-concept in relation to the natural world [
109]. In this regard, Stern et al. [
32] argued that “the step towards intense activism involves a substantial and transformational commitment, including a reframing of key elements of identity” (p. 84). More recently, several authors have stressed that PEBs in general are better predicted when outer variables of social influence have been internalized, as in the case of environmental identity [
110,
111,
112]. As a consequence, the effect of norms can be reconsidered, taking into account the role of identity as a more proximal variable predicting PEBs. From this starting point, Whitmarsh and O’Neill [
113] have shown a wider role of the pro-environmental identity on PEBs, referring to several everyday behaviors, such as waste reduction, eco-shopping and eating, water, and domestic energy conservation. Gatersleben et al. [
103] found a significant effect of pro-environmental identity on recycling, buying fair trade, and avoiding flying on holidays. The importance of environmental identity on PEB has also been shown with reference to volunteering in stewardship activities in local parks [
114]. Going further in the psychological mechanisms behind PEBs, a mediation role of pro-environmental self-identity has been recently outlined in the relationship between biospheric values and PEBs [
115,
116]. In a longitudinal study, Carfora, Caso, Sparks, and Conner [
117] found a moderating effect of pro-environmental self-identity on several PEBs, including reducing food waste, food waste recycling, food packaging recycling, and food purchase.
Second, while affect towards specific PEBs can play a role, the role of a general affective relationship with the environment is presumably a relevant further variable to be considered in a comprehensive framework. In this regard, connectedness to nature and its psychometric measure (CNS) have been conceived as emotional connections with the natural world [
118]. Similarly, the nature relatedness scale (NRS) [
119] assesses the affective, cognitive, and experiential aspects of an individual’s connection to nature, and “encompasses one’s appreciation for and understanding of our interconnectedness with all other living things on the earth” (p. 718). Tam [
120] proposed and empirically validated a measure of dispositional empathy towards nature (DEN), which refers to the dispositional tendency to understand and share the emotional experience of the natural world. The role of emotional bonds with nature on PEBs has emerged in previous research. For example, Hoot and Friedman [
121] reported a significant effect of CNS on a six-item measure of PEBs, including signing petitions for or contributing to environmental causes, product selection based on environmental attributes, voting for political candidates for environmental reasons, membership in environmental groups, and reading publications by environmental groups. Martin et al. [
122] found a positive relationship between connection to nature measured through NRS and PEBs, referring to both household and nature conservation. A similar association has emerged in other studies [
123,
124]. Geng, Xu, Ye, Zhou, and Zhou [
125] considered a measure of both implicit and explicit connections through the Implicit Association Test [
126] and the CNS, and they found a significant association of the former with spontaneous PEBs (i.e., the use of a plastic bag in the laboratory) and the latter with deliberative PEBs, measured through the GEB scale.
1.2. The Role of Parents and Intergenerational Transmission in Children’s Pro-Environmental Behavior
As already mentioned, PEBs are influenced by a “relevant other’s” expectations and actions [
127]. Studies on intergenerational transmission of environmentalism for youngsters are consistent in assuming that parents are the primary sources of PEB development of their children and represent the main (and, for the first years of development, exclusive) social context of children’s pro-environmental practices [
128]. Most of these studies have reported significant parent–child similarities in pro-environmental values, norms, concerns, attitudes, and behaviors [
129,
130,
131], by showing that children who grew up with pro-environmental parents are likely to engage in more pro-environmental behavior as young adults [
132].
Both direct and indirect intergenerational transmission processes in the environment domain are supported by research results. For example, Gong et al. [
133] recently carried out a study on these processes involving a large sample of Chinese families with an early adolescent child (10–15 years). They pointed out that both mothers’ and fathers’ green consumption values were positively associated with adolescents’ green consumption values (i.e., direct transmission). This association was mediated by each parent’s environmentally responsible consumption behavior (i.e., indirect transmission), but only when there was a close parent–child relationship. In her research based on representative data from the parent–child socialization study in Belgium (2012), Meeusen [
131] found that environmental attitudes were significantly related among father, mother, and adolescent child. On the other hand, the author showed that parent–child transmission of environmental concerns passed through the communication about the environment within the family. In those families that frequently talked about the environment, environmental concerns were more effectively transmitted from parents to adolescents. Interestingly, parent–child communication, and more in general parental behavior, had diverse influences depending on the type of pro-environmental behavior. From Matthies, Selge, and Klöckner’s study [
94] on two relevant pro-environmental behaviors in Germany, it emerged that parents influenced the recycling behavior of their school-aged children (age 8–10) via sanctions and their own behavior, while re-use of paper was mainly influenced via communication of problem knowledge.
Research indicates that the parental influence on daily pro-environmental behavior of their children is universal, even though some differences between individualistic and collectivistic cultures have been identified [
134,
135]. Ando et al. [
128], in their research with German and Japanese school-age children, found that environmental behavior of parents (e.g., paper recycling) directly affected the behavior of children, both in Germany and Japan. The findings also showed that parents’ behavior can influence children’s behavior by affecting the perception of seriousness of waste and subjective norms, especially in Japan (i.e., a collectivistic country), and personal norms, but only in Germany (i.e., an individualistic country). Subjective norms have been simply considered by the authors as the children’s experienced expectations of their parents; personal norms have been defined as the feeling of personal moral obligation based on the individual’s personal values, according to Schwartz’s Norm Activation model [
80].
Personal values have been widely considered a central variable in the family relationships and intergenerational transmission processes [
136,
137], and, as mentioned above, their importance in PEBs has been outlined by several empirical studies [
56,
57,
58]. Parent–child value similarity is the result of a complex network of mutual influences among parents, children, and their shared environments [
138]. Transmission is widely acknowledged to be bidirectional with children having an active role and being able to influence their parents [
139]. Children, indeed, perceive their parents’ values and can accept or reject what is perceived to be the parent’s viewpoint [
140,
141]. Perceived parental values have been found to contribute to predict children’s behaviors, such as academic and social behaviors [
142], from childhood to young adulthood.
Fathers and mothers play specific (and non-interchangeable) roles in the transmission of values [
143]. Mothers, who are generally more involved with the daily task of child-rearing and household, seem to be able to share more values with their children than fathers, so much that some studies have supported the hypothesis of a “female lineage” in the intergenerational transmission of values [
140,
144]. Mothers are usually carriers of relational values, such as benevolence and conservation, while fathers tend to give more importance to action values, such as power and stimulation [
145]. Consistently, Power and Shanks’ qualitative study [
146] found that mothers are likely to encourage interpersonal behaviors such as manners and politeness, and adolescents’ involvement in domestic chores, while fathers are more involved in encouraging instrumental behaviors such as assertiveness and independence.
Despite all of this, there has been little examination of how fathers’ and mothers’ ecological values influence children’s ecological values and pro-environmental behavior development [
147]. Most studies have indeed focused on intergenerational transmission of general values rather than of environmental core values [
130].