ntroductionFor a long time, psychology has been predominantly concerned with examining human behavior and how it’s influenced by the environment they live in. But in an era dominated by what humans are doing to the environment and the consequences such as climate change, pollution and poor use of resources or a lack of focus on sustainability, environmental psychology attempts to merge the discipline of traditional psychology with the contemporary issues of the environment to try and understand how best to understand the behavior driving environmental destruction and tackle it efficiently. This piece thus critically looks at the psychologists’ contributions to the promotion of pro environmental behavior focusing on both arguments for their contribution and its effectiveness as well as counter arguments.  The world is facing serious environmental problems related to, amongst others, global warming, urban air pollution, and scarcity of safe drinking water. These problems are, at least partly, rooted in human behaviour (DuNann Winter & Koger, 2004; Gardner & Stern, 2002; Vlek & Steg, 2007), and can thus be managed by changing the relevant behaviors so as to promote environmental quality.Changes in human behaviour are believed to be needed because technical efficiency gains resulting from, for example, energy-efficient appliances, home insulation, and water-saving devices tend to be overtaken by consumption growth (Midden, Kaiser, & McCalley, 2007). Moreover, physical and technical innovations imply behavior changes as well because individuals need to accept and understand them, buy them, and use them in proper ways. This paper discusses environmental psychology’s merits and its potential to help promote environmental sustainability via behavioural changes. We provide a systematic perspective on assessing, understanding, and changing environmental behaviour. We define environmental behaviour broadly as all types of behaviour that change the availability of materials or energy from the environment or alter the structure and dynamics of ecosystems or the biosphere (Stern, 2000). Pro-environmental behaviour refers to behavior that harms the environment as little as possible, or even benefits the environment.Following Geller (2002), we argue that promoting behavior change is more effective when one carefully selects the behaviours to be changed to improve environmental quality, examines which factors cause those behaviours, applies well tuned interventions to change relevant behaviours and their antecedents, and systematically evaluates the effects of these interventions on the behaviours themselves, their antecedents, on environmental quality and human quality of life.  Motivational factors: three lines of research Weighing costs and benefitsVarious studies on environmental behaviour started from the assumption that individuals make reasoned choices and choose alternatives with highest benefits against lowest costs (for example in terms of money, effort and/or social approval). One influential framework is the Theory of Planned Behaviour (Ajzen, 1991). The TPB has proven to be successful in explaining various types of environmental behaviour, including travel mode choice (Bamberg & Schmidt, 2003; Harland, Staats, & Wilke, 1999; Heath & Gifford, 2002; Verplanken, Aarts, Van Knippenberg, & Moonen, 1998), household recycling (Kaiser & Gutscher, 2003), waste composting (Mannetti, Pierro, & Livi, 2004; Taylor & Todd,1995), the purchasing of energy-saving light bulbs, use of unbleached paper, water use, meat consumption (Harland et al., 1999), and general pro-environmental behaviour (Kaiser et al., 1999).Moral and normative concernsA wide range of studies focused on the role of moral and normative concerns underlying environmental behaviour from different theoretical perspectives. First, scholars have examined the value-basis of environmental beliefs and behaviour (De Groot & Steg, 2007, 2008; Nordlund & Garvill, 2002; Schultz & Zelezny, 1999; Stern & Dietz, 1994; Stern, Dietz, & Kalof, 1993; Stern, Dietz, Kalof, & Guagnano, 1995). These studies revealed that the more strongly individuals subscribe to values beyond their immediate own interests, that is, self-transcendent, pro social, altruistic or bio spheric values, the more likely they are to engage in pro-environmental behaviour. Second, studies focused on the role of environmental concern. Different conceptualisations of environmental concern have been used, but environmental concern has mostly been measured by the New Environmental Paradigm scale (Dunlap & Van Liere, 1978; Dunlap, Van Liere, Mertig, & Jones, 2000). These studies revealed that higher environmental concern is associated with acting more pro-environmentally, although relationships are generally not strong (such as Poortinga, Steg, & Vlek, 2004; Schultz & Zelezny, 1998; Vining & Ebreo, 1992).A third line of research focuses on moral obligations to act pro environmentally. These studies are based on the norm-activation model (NAM; Schwartz, 1977; Schwartz & Howard, 1981) or the value-belief-norm theory of environmentalism (VBN theory; Stern, 2000; Stern, Dietz, Abel, Guagnano, & Kalof, 1999). The NAM and VBN theory appeared to be successful in explaining low-cost environmental behaviour and ”good intentions” such as willingness to change behaviour (Nordlund & Garvill, 2003; Stern et al.,1999), political behaviour (like Ga¨ rling, Fujii, Ga¨ rling, & Jakobsson, 2003), environmental citizenship (e.g., Stern et al., 1999), or policy acceptability (such as De Groot & Steg, in press; Steg, Dreijerink, & Abrahamse, 2005), but they appear to have far less explanatory power in situations characterised by high behavioural costs or strong constraints on behaviour, such as reducing car use (such as Bamberg & Schmidt, 2003; Guagnano, Stern, & Dietz, 1995; Hunecke, Blo¨baum, Matthies, & Ho¨ger, 2001). In such settings, the TPB appears to be more powerful in explaining environmental behaviour (Bamberg & Schmidt, 2003), probably because the TPB considers a wider range of factors, notably non-environmental motivations and perceived behavioural control.A fourth line of research focused on the influence of social norms on behaviour. The theory of normative conduct (Cialdini, Kallgren, & Reno, 1991; Cialdini, Reno, & Kallgren, 1990) distinguishes two types of social norms. Injunctive norms refer to the extent to which behaviour is supposed to be commonly approved or disapproved of. Descriptive norms reflect the extent to which behaviour is perceived as common. The extent to which injunctive and descriptive norms influence behaviour depends on the saliency of a particular norm. This theory has been validated in a series of experimental studies about littering in public places (Cialdini et al., 1990, 1991).AffectSome studies have explicitly examined the role of affect in explaining environmental behaviour, mostly in relation to car use (Gatersleben, 2007). It appeared that car use is significantly related to affective and symbolic factors. Most studies on the role of affective and symbolic motives were exploratory and not theory-based. Steg (2005) demonstrated that Dittmar’s (1992) theory on the meaning of material possessions provides a promising perspective. This theory proposes that the use of material goods fulfils three functions: instrumental, symbolic, and affective. Steg (2005) showed that car use is most strongly related to symbolic and affective motives, while instrumental motives are less important. Dittmar’s theory offers a promising perspective on individual motives to buy and use material goods. An obvious question for further research concerns the role of symbolic and affective motives in other domains than car use.An integrative perspective on environmental motivation: The three general lines of research just described involve rather different antecedents of environmental behaviour. All three perspectives proved to be predictive of at least some types of environmental behaviour. However, as yet it is not clear which perspective is most useful in which situation. Although moral and normal frameworks appear to be more successful to explain low cost behaviour and actions with environmental intent (Stern, 2000), systematic research on the range of application of each theoretical perspective is lacking.The three theoretical perspectives are not mutually exclusive. Various scholars have integrated concepts and variables from different theoretical frameworks, showing that behaviour resultsfrom multiple motivations (Guagnano et al., 1995; Harland et al., 1999; Heath & Gifford, 2002; Stern et al., 1993, 1995). Goal framing theory (Lindenberg, 2001a, 2001b, 2006) explicitlyacknowledges that behaviour results from multiple motivations. This theory postulates that goals govern or ”frame” the way people process information and act upon it. When a goal is activated (that is, when it is the ”focal” goal or ”goal-frame”), it influences what a person thinks of at the moment, what information he is sensitive to, what alternatives he perceive, and how he will act. Three general goal-frames are distinguished: a hedonic goal frame ”to feel better right now”, a gain goal-frame ”to guard and improve one’s resources”, and a normative goal-frame ”to act appropriately”. The hedonic goal-frame is a priori strongest, while especially the normative goal-frame is in need of external social and institutional support in order to become focal. Goal-framing theory proposes that motivations rarely are homogeneous. One goal is focal and influences information processing the most (that is, it is a goal-frame), while other goals are in the background and increase or decrease the strength of the focal goal. Thus, multiple goals are active at any given time. When background goals are compatible with the goal-frame, theystrengthen it. But when the goal-frame and background goals are in conflict, the latter weaken the strength of the goal-frame. Lindenberg and Steg (2007) reviewed the literature in environmental psychology in light of goal-framing theory. The three goal-frames remarkably coincide with the three theoretical frameworks commonly used in environmental psychology, as discussed above. That is, theories and models on affect focus on hedonic goal-frames, the TPB is focused on gain goal-frames, while the NAM, VBN theory and research on values and environmental concern focus on normative goal-frames. Thus, goal-framing theory seems to be suitable as an integrative framework for understanding environmental behaviour. However, as yet goal-framing theory has not been tested in the environmental domain, and little is known about the way in which multiple motivations may affect environmental behaviour. Lindenberg and Steg (2007) list various topics that should be addressed.Contextual factorsThe theories and perspectives discussed above focus on individual motivations influencing environmental behaviour. Obviously, human behaviour does not depend on motivations alone.Many contextual factors may facilitate or constrain environmental behaviour and influence individual motivations (O¨ lander & Thøgersen, 1995; Stern, 1999; Thøgersen, 2005; Van Raaij, 2002). For example, the availability of recycling facilities, the quality of public transport, the market supply of goods, or pricing regimes can strongly affect people’s engagement in pro-environmental behavior (Santos, 2008; Van Diepen & Voogd, 2001; Vining & Ebreo,1992). In some cases, constraints may even be so severe that behaviour change is very costly and motivations make little difference in the environmental outcome (Corraliza & Berenguer, 2000; Guagnano et al., 1995; Lu¨ demann, 1998). So, it is not only important to consider intra-personal factors such as attitudes, norms and habits, but also contextual factors such as physical infrastructure, technical facilities, the availability of products, and product characteristics.In environmental psychology so far, except for a few studies (Black, Stern, & Elworth,1985; Guagnano et al.,1995; Hunecke et al., 2001), contextual factors have not been examined systematically, nor are contextual factors included in the theoretical approaches discussed above. The TPB only considers individuals’ perceptions of contextual factors, as expressed in perceived behavioural control. This is remarkable, given that environmental psychology aims to study transactions between humans and their environment, and thus should be particularly interested in examining the effects of contextual factors on behaviour.Contextual factors may operate in four different ways. First, they may directly affect behaviour. For example, one cannot travel by bus when no bus service is available, while a free bus ticket may result in an increase in bus ridership (Bamberg & Schmidt, 1999; Fujii & Kitamura, 2004). Second, the relationship between contextual factors and behaviour may be mediated by motivational factors such as attitudes, affect, or personal norms. For example, the introduction of recycling facilities may result in more positive attitudes towards recycling (because it is more convenient), and positive attitudes may in turn result in higher recycling levels.Third, contextual factors may moderate the relationship between motivational factors and behaviour, and the effects of contextual factors on behaviour may depend on personal factors (Geller, 1995). For example, environmental concern may only result in reductions in car use when feasible alternatives are available, and recycling facilities may promote recycling only among those high in environmental concern. Fourth, and related to the third point, followinggoal-framing theory, it may well be that contextual factors determine which type of motivations (and thus which goal-frame) most strongly affects behaviour. For example, normative goals may be strongly related to frequency of recycling when facilities are available (Guagnano et al., 1995), while gain or hedonic goals may be prominent if recycling facilities are poor. Given the significance of contextual factors for environmental behaviour, studies are needed about the role of contextual factors vis-a` -vis motivational factors, following our suggestions above. This should preferably be done in collaboration with such experts as architects, urban planners, industrial designers and technologists who do explicitly consider the effects of contextual factors. Multiple levels of analyses in measurement and statistical models (Snijders & Bosker, 1999) may be very useful to examine to what extent behaviour depends on contextual factors, motivational factors, and the interaction between them. Such research may lead to intervention programmes aimed at behaviour changes for which external barriers have to be eliminated while feasible alternatives are put in place.Habitual behaviorThe theoretical frameworks largely imply that individuals make reasoned choices. However, in many cases, behaviour is habitual and guided by automated cognitive processes, rather than being preceded by elaborate reasoning. Aarts, Verplanken, and Van Knippenberg (1998) defined three important characteristics of habits. First, habits require a goal to be achieved. Second, the same course of action is likely to be repeated when outcomes are generally satisfactory. Third, habitual responses are mediated by mental processes. When people frequently act in the same way in a particular situation, that situation will be mentally associated with the relevant goal-directed behaviour. The more frequently this occurs, the stronger and more accessible the association becomes, and the more likely it is that an individual acts accordingly. Thus, habitual behaviour is triggered by a cognitive structure that is learned, stored in, and retrieved from memory when individuals perceive a particular situation. Habits refer to the way behavioural choices are made, and not to the frequency of behaviour. Aarts and Dijksterhuis (2000) developed a so-called response-frequency measure of general habit strength, relying on the assumption that goals automatically activate mental representations of habitual choices. This measure is far more accurate than simply asking people how frequently they engage in a particular behaviour, as it focuses on how choices are made. The measure has been successfully employed in various studies on environmental behaviour (Aarts & Dijksterhuis, 2000; Aarts et al., 1998; Klockner, Matthies, & Hunecke, 2003). Habitual behaviour may involve misperceptions and selective attention: people tend to focus on information that confirms their choices, and neglect information that is not in line with their habitual behaviour. In general, habits are reconsidered only when the context changes significantly. For example, Fujii and Ga¨ rling (2003) and Fujii, Ga¨ rling, and Kitamura (2001) found that temporarily forcing car drivers to use alternative travel modes induced long-term reductions in car use. The impacts of such temporary changes were particularly strong for habitual car drivers. This suggests that habitual drivers have in accurate, and modifiable perceptions of the pros and cons of alternative transport modes. In order to design effective interventions to modify habitual environmental behaviour, it is important to consider how habits are formed, reinforced and sustained. Computer simulation is an interesting methodology to study the formation and reinforcement of habits, for example, by formalising behavioural determinants and processes in simulated agents (Jager & Mosler, 2007, for an overview). ConclusionsEnvironmental psychologists have an important role to play in the management of environmental problems by the promotion of behavioural changes. Behavioural interventions are generally moreeffective when they are systematically planned, implemented and evaluated. Four key issues to be addressed are: identification of the behaviour to be changed, examination of the main factors underlying this behaviour, application of interventions to change the relevant behaviours and their determinants, and evaluation of intervention effects on the behaviour itself, its main determinants, environmental quality, and human quality of life.Interdisciplinary collaboration is needed to effectively address these issues, because environmental problems are not just psychological problems; they are also ecological, technological, and socio-cultural problems. Schoot Uiterkamp and Vlek (2007) gives a detailed discussion on the added value, conditions, and pitfalls of interdisciplinary research, illustrations of how these four issues have been studied so far are indicated in various topics for future research. These can be summarised as follows:It is advisable to measure actual behaviour whenever possible, and to pay attention to the validity and reliability of self reported behaviour measures.The conditions under which a particular theory is most successful in explaining environmental behaviour need more attention, and the merits of various theories should be studied more systematically. A theory-driven approach towards the behavioural components of environmental problems will provide a strong basis for understanding and managing these problems (following Kurt Lewin, 1951, p. 169): ”Nothing is as practical as a good theory”.The effects of contextual factors on environmental behavior need to be examined in more detail, as well as how these factors affect various environmental behaviors vis-a` -vis motivational factors. This may lead to extensions of existing theoretical models.It is important to study for which types of behavior and under which conditions which intervention strategy is most effective for encouraging pro-environmental behaviour. In particular, the role of various types of rewards and punishments needs further scrutiny.Interventions need to be evaluated following experimental research designs. Changes in the relevant behaviour, behavioural antecedents, environmental quality, and individual quality of life should be assessed before and after the implementation of an intervention, and ‘treatment’ effects should be compared to those in a control group not exposed to the intervention.The way subjects adapt to (the effects of) environmental policies and why policy preferences change over time such as before and after policy implementation, need to be clarified. 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