1.1 Popularity of serious games has grown

Games were primarily used for entertainment but have been applied to nonentertainment functions such as education and motivation at the workplace. These are termed as serious games. The adjective ‘serious’ refers to games developed for nonentertainment industries like defence, education, scientific exploration, health care, emergency management, city planning, engineering and politics (Abt, 1987). They add the elements of fun, competition, and engagement to the intended purposes such as learning in education and changing individual's behaviour to be more environmentally sustainable.

The popularity of serious games in education has grown worldwide, with an estimated market worth $5.94 billion in 2020 and a growth rate, over the last 2 years, of nearly 100% per year (Gaikwad, 2022). Additionally, 97% of all US teenagers play digital games (Lenhart et al., 2018) and 74% of teachers implement digital game-based learning (DGBL) into their lessons, enabling serious games to be highly relatable to the general population (Takeuchi & Vaala, 2014). The increasing awareness of serious games or game-based learning, growing investment by recognized companies into the industry and growing need for serious gaming on mobile are the major drivers of the increasing popularity of serious games in the Asia-Pacific region (Zhonggen, 2019). The coronavirus disease 2019 pandemic and nationwide lockdowns, as well as governments giving attention to educational gaming, are some of the factors expected to augment the adoption of serious games in the future. It is estimated that the serious games market will keep growing quickly to reach a value of $32.72 billion by 2030 (Gaikwad, 2022). This predicted economic growth reflects a future significant usage among consumers and enterprises to adopt serious games in training and development.

Other than the gaming industry, serious games are also growing rapidly in the field of academic research. There has been an exponential growth in the number of research papers published in the field, starting from one publication on serious games in Scopus in 1984 to about 950 papers in 2019. This indicates the increased interest of the research community in serious games (Irmade et al., 2021). The drive is to elucidate the benefits and cons of serious games and the mechanisms underlying the impacts of serious games. Advantages of serious games include increased motivation to do work, enhanced learning and increased social bonding among participants (Bergeron, 2008; Breuer & Bente, 2010; Ramachandran et al., 2016). Disadvantages include the possible increased levels of anxiety and aggression from playing violent games, but this effect is still under debate (Susi et al., 2007). On average, the pros of serious games outweigh the cons (Connolly et al., 2012; Girard et al., 2013), accounting for the rise in the popularity of serious games in various industries.

Similarly, the popularity of serious games in environmental education has grown. The last systematic literature review conducted in 2019 revealed that the number of published serious games about sustainable development rose from 2 during the years 1990–1995 to 26 during the period 2014–2018 (Stanitsas et al., 2019). This paper, together with an earlier review, revealed that serious games in general enhanced learning experience and cognitive ability, as well as increased engagement in learning about sustainability (Madani et al., 2017; Stanitsas et al., 2019). Nevertheless, the literature on these serious games for environmental education highlights the limitations: lack of a systematic approach to examining the pedagogical efficacy of serious games and the presence of only a few studies investigating the long-term impacts of serious games (Hallinger et al., 2020; Madani et al., 2017; Stanitsas et al., 2019). Indeed, serious games have an immense potential of changing perceptions about environmental conservation and of increasing proenvironmental behaviours; these are the ultimate intended outcomes of environmental education (Morganti et al., 2017). Limitations of past studies aside, there is a need to consolidate the defining features of impactful serious games, to guide the creation of future serious games.

1.2 Why games are popular?

Games exhibit features that tap on the basic motivators of humans, enabling the amotivated and even motivated students to have an increased drive to learn, when compared to the conventional teaching style (Juan & Chao, 2015; Madani et al., 2017). These basic motivators can be categorized in a hierarchical manner based on Maslow's framework: physiological needs, safety needs, love and belonging, esteem and self-actualization (Madani et al., 2017). Physiological needs are met with the attainment of resources in the game, whereas territoriality (like owning land) and having sufficient health feed safety needs. Interacting and perhaps bonding with others provide a sense of belonging (Vella et al., 2019). When achieving a goal in the game, the associated sense of accomplishment increases one's self-esteem (Juan & Chao, 2015). Finally, games require problem-solving or creative thinking skills to attain a goal, this fulfils the motivator of self-actualization (Madani et al., 2017). Undeniably, games capitalize on instinctive human motivation to attract people to play and sometimes replay (Chappin et al., 2017).

1.3 What is the current technology in serious game?

As outlined by Prensky (2001), DGBL is a particular type of game-based learning. It combines the educational content and games on computers or online to stimulate learners' interest and provide them with the opportunity for continuous learning. Interactive technology such as virtual reality could foster an effective learning process, especially among young learners (Latif, 2007). Alongside the advancement of technology in recent decades, digital games have become more accessible, portable and affordable for the masses. Digital games can take on the form of web-based apps, computer software or mobile applications.

1.4 Aims

In this paper, we conducted a systematic search for papers that examined serious games used for environmental education. Our systematic review revealed four specific areas for a general discussion on the subject. First, we reviewed the reasons for the increased use of serious games in education. Then, we examine the appropriateness of serious games in environmental education and identify the features of the successful ones. Third, we discuss the current gaps and challenges. Finally, we examine the current trend of this topic.

Recent reviews on ‘serious games for environmental education’ identified the aims of the serious games, that is, what topics were they trying to teach, as well as to examine the main effects of serious games on intended educational outcomes (Boncu et al., 2022; Scurati et al., 2020; Stanitsas et al., 2019). The consolidated view from these studies is that serious games facilitate learning of environmental knowledge and encourage proenvironmental perception and behavioural change. Our study builds on this and is also unique in that it synthesizes the results of past studies to consolidate the features of successful games and provides an insight into the current trends in the creation of new games.

4.1 Serious games can motivate intrinsically and extrinsically

Learners range in their levels of motivation for learning, and serious games can cater to this range of motivation. On one end of the scale, there is the amotivated, which refers to people who lack the drive to do something. Then comes extrinsic motivation, which refers to doing something because it leads to a separable outcome, and finally on the other end of the scale intrinsic motivation, which refers to doing something because it is inherently interesting or enjoyable (Deci et al., 2001). For the amotivated, serious games appeal to the basic human motivators and can increase motivation through extrinsic means like the rewards and points incorporated in games (Sealover & Henderson, 2005). For those who are extrinsically motivated by things such as grades and job opportunities, the enjoyment while playing can transform the motivation into an intrinsic one (Deen & Schouten, 2011; Drummond et al., 2017). For the already intrinsically motivated, games provide rewards that can shift the motivation to an extrinsic one, which might in turn decrease the enjoyment in learning (Deci et al., 2001). Nevertheless, games play upon the different motivational levels of players and can increase or decrease the enjoyment in learning.

Although knowledge has been perceived as the main goal in environmental education, it has been reported that having a high environmental knowledge alone is not enough to translate into proenvironmental actions (Boncu et al., 2022). To encourage the audience to be active advocates of environmental issues, it is important to nurture personal responsibility towards nature. One study revealed that one can be motivated to practice good environmental behaviour with the combination of immersion, empathy and personal connection to the story (Chiang, 2021). Another study revealed that a combination of knowledge, values and personal connection managed to encourage a 76%–94% increase in proenvironmental behaviour (Kaiser et al., 1999).

Enercities is a game developed with the aim of educating on environmental sustainability (Janakiraman, 2020; Janakiraman et al., 2021). Players role-play as a city planner. To win the game, players need to be able to balance environmental well-being, citizen's happiness, resource exploitation and economic growth in a mission to build a sustainable city. Mechanistically, the game extrinsically motivates players when they attain resources and finances. It also intrinsically motivates with novel situations, appealing aesthetics and challenges; these three are elements of intrinsically motivated behaviour (Deci et al., 2001).

4.2 Complexities behind environmental issues can be illustrated using serious games

Serious games are especially appropriate for environmental education due to the complexities behind environmental issues (e.g., social responsibility and governance), and the involvement of multiple stakeholders in environmental issues (Ambarwati & Ardi, 2019). Given that there are multiple considerations such as economy, governance and availability of natural resources, decisions made in the game may require players to draw on knowledge from multiple disciplines. Serious games often simulate the real world, allowing participants to deal with environmental issues within the confines of a fail-safe environment, yet enabling the consequences of decisions to play out (Koenigstein et al., 2020; Schulze et al., 2015). The use of role-play during the game (Janakiraman et al., 2021) play can help players understand the perspectives and the demands of different roles by playing with or against each other. As such, learning in the affective domain takes place (Janakiraman et al., 2021). Conflict might arise through the gameplay because of opposing interests, which are reflective of the real world. Consequently, in resolving conflicts, players may learn transferable skills such as communication, negotiation, and mitigation (Ambarwati & Ardi, 2019; Segoni, 2022).

For example, a game called ‘The Climate Adaption’ (Neset et al., 2020) was developed to educate on sustainable development, encouraging systems thinking and the creation of democratic action-oriented strategies. The game has an objective of integrating knowledge of climate adaptation with management decisions while considering other dimensions of the proposed actions such as costing, climate variabilities and conflicting multistakeholders' demands. The game requires the player to reduce the impact of climate change. In each mission, the players were given a few alternatives, each with different costs and consequences to decide on as a group. They would also have to consider different scenarios of climate change. The game simulates a long-term climate adaptation whereby players need to make different decisions every 10–50 years until the year 2100.

Despite the potential of serious games in conveying complex situations, there are some challenges of incorporating serious games in structured lessons within a classroom setting. As most, if not all, lessons in long-standing classroom teaching are already predetermined and structured, it can be challenging to figure out the appropriateness of this approach in a time-limited teaching session. Additionally, there is still a stigma around the utilization of games as educational tools in a conventional classroom and many educators may not be comfortable with adopting a novel approach of teaching.

4.3 Serious games support learning in multiple cognitive dimensions

Our tabulated records demonstrate that participants learn in multiple ways when playing serious games (see ‘Table 1’ explained in ‘Results and interpretation’ section). These include knowledge increase, attitude change, behaviour change, awareness, empathy, connection with others and communication skills. Therefore, serious games can benefit learning in multiple cognitive dimensions, from the lower-order thinking skills such as remembering and understanding (e.g., Ambarwati & Ardi, 2019; Juan & Chao, 2015) to the higher-order thinking skills such as synthesis and evaluation, and these critical thinking skills would then translate to changes to emotions, attitudes and behaviours (Thomas, 2002).

Serious games in environmental education have been documented to induce systems thinking, which is the ability to understand the interrelationships between different individuals in an interconnected system (Aronson, 1996). A study was done on a group of individuals who were invited to play a simulation game named ‘Red Redemption's Fate of World’ featuring a 200-year period of societal and environmental impacts of global warming. This group was reported to show a higher degree of environmental systems thinking as compared to the control group (Waddington & Fennewald, 2018).

4.4 Increase in the number of existing games modified with a green message enables the environmental message to reach out to a wider audience

In response to the increased demand for environmental education and awareness, an increasing number of existing games have been observed to include an environmental message (Tragazikis & Meimaris, 2009). Specifically, the mechanism of the game is retained and the content is altered to communicate environmental issues. In short, the game communicates environmental awareness by transforming the ‘for-fun’ game into a serious game aimed at raising environmental awareness.

The modification of commercial games to include a green message caters to the aim of knowledge acquisition or status quo realization. There is a focus on developing familiarity with the environmental topic (Ouariachi et al., 2019). The games mostly communicate the cause and effect of certain decisions instead of encouraging critical thinking in providing solutions for the worrying decline of environmental health. Apart from that, the games sometimes leave out other important dimensions such as social and economic factors, which should be incorporated to ensure that a holistic intervention is implemented to tackle complex environmental issues (Ouariachi et al., 2019).

An example of this is the Monopoly Go Green edition. The game still revolves around buying, selling, and trading property and the green twist made is the additional option of making the property more environmentally friendly with solar and wind energy (Vincent, 2021). The mechanism of the game remains the same as that of the original Monopoly game: a higher investment in property will increase its value. There is no clear communication on how this green option is beneficial to nature. The end goal of the game is still about monopolizing all available property and becoming the richest player.

Digital open-world and sandbox games are highly adaptable to be redesigned as serious games as the mechanics are more fluid and customizable. An example of this is Minecraft, which is a pixelated, procedurally generated three-dimensional virtual world developed by Mojang studio, and Minecraft has been modified to encourage people's interest in environmental issues. The developer is taking a serious effort to transform the commercially designed video game into an educational tool. In 2016, they announced a classroom-friendly version of Minecraft known as Minecraft: education edition. Academic institutions are encouraged to create educational content in the Minecraft education library and all educational contents are made available with the purchase of educational licences. In contrast, the commercial Minecraft requires multiple in-game microtransactions to obtain more in-game content (van Berlo et al., 2016).

In response to the availability of the education-tailored version of Minecraft, there has been a rise in the number of environmental education content created by institutions (United for Wildlife - Minecraft - We Are The Rangers, n.d.) and environmental NGOs (Minecraft, n.d.) in the Minecraft library. For instance, in 2018, the Zoological Society of London together with the Royal Foundation collaborated with Minecraft under the United for Wildlife initiative to create five new adventure worlds in Minecraft named ‘We Are The Rangers’. The world was developed with the setting of African Savannah where players can role-play as wildlife rangers to help save endangered species. They do this by collecting elephant faecal matter for DNA coding, working with communities to mitigate human–elephant conflicts and saving pangolins from wildlife trades. A total of 113,000 players were reported to take part when the pack was launched, and this pack is still popular to this date in Minecraft: Education Edition (United for Wildlife - Minecraft - We Are The Rangers, n.d.).

Aside from developing educational content in Minecraft: Education Edition, Minecraft started to bring in serious games into the commercial version (Java edition and Bedrock Edition) in late 2018. By partnering with World Wildlife Fund for Nature (WWF), the developer introduced pandas in the global update of all Minecraft editions to raise awareness on this species and its conservation (Pandas and more now on Minecraft Bedrock, Stone, 2018). The global update invited players from all over the world to plant bamboo and build panda habitats within the game and this communicated the importance of habitat conservation for the survival of this vulnerable species. The commercial Minecraft not only took up the challenge of incorporating serious games, the developer donated $100,000 to WWF's global conservation work after players had placed 10 million bamboo blocks in-game. A year later, Minecraft introduced bees in its global update to raise awareness on the important roles of bees as pollinators, which is vital for a healthy ecosystem. Indeed, the incorporation of an environmental message in an existing popular gaming platform can facilitate the dissemination of environmental awareness. In the year 2021, the number of monthly active users of Minecraft is 93 million (Curry, 2022), suggesting the potential of reaching out to a large audience base.

5.1 Immersive experience

Most serious games incorporate a back story, an epic quest and roleplay activities to engage the players (Naul & Liu, 2020). These elements encourage players to focus on the game by engaging with the players' emotion and cognition (Lai & Yang, 2015). This deep connection with the game activities often results in an immersion effect, which is also known as flow experience (Wang et al., 2019). Flow experience is explained by Flow Theory as a state of full focus and attention given to the present moment. During the flow experience, other irrelevant emotions, sensations and thoughts are blocked, resulting in optimum concentration and performance (Csikszentmihalyi, 1988).

The usage of technology such as virtual reality or mixed reality in serious games can increase the immersion and enable the message of environmental education to be conveyed effectively. Immersive experiences encountered during serious gaming sessions facilitate effective learning of procedural and descriptive knowledge (Wang et al., 2019).

5.2 Meaningful engagement

Serious games in multiplayer mode encourage interactions and engagement among players (Garneli et al., 2021). Positive engagement during gaming sessions carves out an easy path for the students to achieve the learning objectives (García-Bárcena & García-Crespo, 2007; Vasiliou & Economides, 2007). This is because games nudge the players to either play with or against other players/colearners resulting in meaningful engagement such as thoughtful discussions on complex conservation issues (Neset et al., 2020).

The engagement among players allows peer-to-peer and collective learning (Koenigstein et al., 2020), beneficial to the teaching and learning process. As some serious games were designed to allow dialogues on complex environmental issues, innovative attitudes and critical thinking within these social settings might also be encouraged through these in-game dialogues and debates (Vasconcelos & Seingyai, 2022).

5.3 Learning by doing

Environmental issues generally require hands-on actions and interventions. Serious games enable participants to experience the process, conduct actions and strategize, all of which are often limited during didactic conventional teaching. This process facilitated by serious games is also known as learning by doing, and has been observed to enhance the knowledge acquisition process among learners (Thirouard et al., 2015). Hands-on learning also helps the memory consolidation process, which benefits long knowledge retention (Ninaus et al., 2015) for players. Practical movements also can transform the experience of procedural and descriptive knowledge into concrete learning (Wang et al., 2019).

5.4 Simulation of real-world environmental problems

Serious environmental games designed to simulate real-world environmental problems encourage higher-order thinking, specifically during the creation of problem-solving strategies (Gros, 2007). Real-world simulations in serious games allow the participant to see, plan, implement and strategize without the fear of making mistakes or of failing (Rumore et al., 2016). This also encourages systemic thinking. With systemic thinking, the learners can understand that their presence and actions are ‘a part of the bigger picture’ and can hence be motivated to be part of the transformational unit of the ecosystem (Dieleman & Huisingh, 2006).

Apart from the complex real-world simulation in serious games, technology such as virtual reality has enabled the simulation of impossible real-world environments (e.g., organs in the human body, ocean exploration) (Chiang, 2021). All these simulations benefit the learning experience in a positive manner making serious games outstanding learning tools.

5.5 Autonomy in decisions

Autonomy is a personal perception on the ownership of choice held by an individual when making a decision (Mandigo et al., 2008). Autonomy in serious games can be as simple as deciding on aesthetic looks of chosen characters and game tokens built (Leventhal, 2018) or as complex as deciding next actions and consequences (Chik, 2014).

Elements of autonomy in serious games empower the learners to take ownership of their decisions and hence to stay engaged during the learning sessions (Wouters et al., 2013). As serious games allow multiple paths to achieve the aim, low-achiever learners have been observed to be able to keep up with the high achievers by embarking on alternative paths to win the game (Cheng et al., 2013). The ownership of decision and multiple mastery paths give rise to autonomy, which contributes to the success of serious games in environmental education.

5.6 Hosting by moderator

The presence of a moderator has been reported to be another key feature of successful games as the guidance provided throughout the process helped the audience to relate better to the environmental message delivered by the serious games (Taylor, 2014). Additionally, the debriefing at the end plays an important role. The conclusion of the experience by the moderator, as well as the self-reflection by participants, contributes to the learning (Crookall, 2014). Successful moderation through guidance and debriefing contributes to the participants' learning experience and hence is a factor in successful serious games.