A perspective on the human dimensions of a transition to net­ zero energy systems

Net-zero energy systems are critical for reducing global temperature change to 1.5 ◦ C. Transitioning to net-zero systems is simultaneously a technological and a social challenge. Different net-zero configurations imply different system and lifestyle changes, and strongly depend on people supporting and adopting these changes. This Perspective presents key insights from the social sciences into factors that motivate low-carbon behaviour and support for low-carbon technologies, policies, and system changes that would need to be addressed to successfully design, develop, implement, and operate net-zero systems. As there is no single net-zero solution, and configurations may differ from region to region, we discuss cultural and regional factors that can enable or inhibit the implementation of net-zero systems on a global scale.


Introduction
To limit climate change to 1.5 • C, global carbon emissions from energy supply and demand need to be reduced, and any remaining carbon emissions may need to be offset to prevent further warming [55]. The world's nations are setting ambitious targets to achieve net-zero emissions around mid-century, including the United States and the European Union pledging net zero by 2050, and China by 2060 [40].To achieve such net-zero energy systems, changes in technology and human behaviour are critical [55]. Notably, net-zero energy systems imply using less energy overall and/or using energy more efficiently, as well as shifting to low-carbon energy sources (e.g., renewables) and technologies (e.g., electric vehicles; [27,47,122]. It is therefore critical to understand what motivates people to change their behaviours to reduce carbon emissions and what influences public acceptability and adoption of low-carbon technologies and energy system changes. Next, many net-zero energy systems imply the implementation of negative emission technologies that offset remaining carbon emissions (e.g., carbon capture and storage), making it important to understand which factors affect the level of support of such technologies [28]. Importantly, net-zero energy systems are not limited to one type of behaviour, technology, or region. Instead, it is a system-level transition of a global scale that requires multiple solutions tailored to different cultural, economic, geographic, historical, political, and social structures across different countries and regions [86]. Therefore, human dimensions are at the heart of net-zero energy systems, making transitioning to net-zero systems simultaneously a technical and a social challenge ( Figure 1).
It has been widely acknowledged that the social sciences play a key role to effectively address the human dimensions of net-zero energy systems (e.g., [24,49,102,103,112,128]. In this Perspective, we synthesize key insights from the social sciences about how to transition to net-zero energy systems. We focus on factors influencing three critical areas of inquiry: factors influencing low-carbon behaviour, factors influencing public acceptability of technologies and system changes inherent to net-zero systems, and cultural aspects relevant to net-zero energy systems. This Perspective focuses at the micro level of individuals and households, while acknowledging the importance of broader meso (e.g., communities, organisations) and macro (e.g., society, nations) levels.

Low-carbon behaviour
No single technology alone, negative emission technologies included, can reduce global warming to 1.5 • C. There is agreement among climate scientists that reducing overall energy demand, using energy more efficiently, and shifting to cleaner energy sources and technologies are critical for reducing global carbon emissions [47,122]. Changes in everyday energy behaviours of individuals and households, in particular behaviours related to mobility, housing, and food, have a substantial potential to reduce carbon emissions [27,35,55,74,114] (see Table 1). Lifecycle analyses have identified behaviours with highest carbon emission savings potential in different behavioural domains, including reducing the use of motor vehicles (mobility), retrofitting and renovating homes (housing), and eating less meat and dairy (food) [57]. Across all behavioural domains, carbon emissions can be most effectively reduced by prioritising efficiency improvements (e.g., energy-efficient light bulbs) rather than curtailments (e.g., switching off lights) [43], and by moving from a linear economy (produce, short-term use, and dispose) to a circular economy (long-term use, reuse, and zero waste) [55].
Shifting to low-carbon energy sources and technologies requires not only one-time adoption of the relevant sources and technologies (e.g., putting solar panels on the roof), but also actions to maintain them and changes in everyday behaviours in order to use them efficiently. Notably, net-zero systems that are heavily dependent on intermittent renewable energy sources (e.g., solar, wind) will be more efficient, reliable, and sustainable when people adjust their energy demand to match the supply of energy from renewable sources, which will also prevent network oversaturation at peak times. People can install technology that match energy demand and supply (e.g., automatically switching appliances on and off) or change their user behaviour (e.g., not using appliances at peak times) (see Table 1).
Besides their own energy-related actions, people can influence lowcarbon actions and policies of business, organisations, and governments, via civic channels [55]. For example, people can choose brands and products with low or zero carbon footprint, boycott brands and products with high carbon footprint, vote for political parties that support climate action, and hinder or support the implementation of energy policies, technologies, and system changes by signing petitions and protesting, among others.
Albeit critical for realizing net-zero systems, people do not always consistently engage in relevant low-carbon behaviours. People may not always know how to save energy and/or use energy most sustainably. Indeed, when asked how to effectively conserve energy, US participants mostly mentioned curtailment behaviours (e.g., change thermostat settings) rather than efficiency behaviours (e.g., insulate homes), and underestimated energy use of high-carbon activities (e.g., transporting goods by trucks) and technologies (e.g., air conditioner) [8,65]. Correcting such misperceptions could help people reduce their carbon footprint. Yet, while important, increased knowledge is often not enough to encourage low-carbon behaviour [2] and the adoption of low-carbon technologies [17]. Notably, even if people have the knowledge, they may not engage in low-carbon behaviour if they are not motivated to do so. The critical question is therefore what motivates people to engage in low-carbon behaviours.

Perceived costs and benefits of low-carbon behaviours
People are more likely to engage in low-carbon behaviours when they associate these behaviours with higher benefits and lower costs and risks [110]. For example, high upfront costs of low-carbon technology may reduce the likelihood of adoption [23,60]. Accordingly, subsides and cost deductions can encourage low-carbon actions, such as cash incentives for recycling [69], discounts on insurance premium for more sustainable driving [14], and a free month travel card to promote the use of public transport [117].
Importantly, not only financial costs and benefits influence people's behavioural choices. Other individual consequences of net-zero systems, such as efforts and convenience of installing, using, and maintaining such systems, comfort (e.g., thermal comfort, easiness of cooking and heating), and autarky and independence in energy supply are also important to people [62,133]. Therefore, technological and infrastructural changes that lower the behavioural costs of low-carbon options could facilitate their adoption, such as improved facilities for recycling [45]. In a similar vein, people prefer to reduce carbon emissions from their energy use by means of technological and/or efficiency solutions, such as electric and/or hydrogen fuelled vehicles and energy-efficient heating systems, rather than by changing (or giving up) certain behaviours, such as travelling less and lowering the thermostat [4,81].
Furthermore, people not only consider personal costs and benefits, but are motivated to achieve benefits for the environment and/or other people [78,133]. Acting in favour of the environment and others can feel meaningful and evoke positive affect, which motivates action [123,124]. Interestingly, emphasizing the benefits for health and comfort and the environment may motivate low-carbon behaviour more than emphasizing financial benefits ( [7, 15, [93]).
Next, social costs and benefits, namely seeking social approval and avoiding social sanctions, are a powerful motive for low-carbon behaviour. People are influenced by what other people do, think, or value, making social influence a potentially effective strategy to promote low-carbon actions [1,2,19]. In net-zero energy systems, social influence can take place through bottom-up initiatives (e.g., local energy cooperatives), that appear to promote low-carbon actions among their members [73,95,98]. Interestingly, people join local energy initiatives not only for environmental reasons, but also to meet and connect to others, which implies that local energy initiatives can motivate low-carbon actions among those who are not primarily motivated for the environment [99]. Social influence can also take place through intermediaries, such as real estate agents, architects, and car dealers, who inform and orientate people in choices with high carbon-reduction potential [29]. Moreover, low-carbon alternatives (e.g., electric vehicles, local renewable energy systems) can signal something positive about their owners to themselves and others, which motivates adoption [75,76].

Values
People differ in the extent to which they consider different costs and benefits of low-carbon behaviours and technologies, depending on the values they prioritise. Values are general goals or ideals that people strive for in their lives [94]. People are motivated to act in ways that support their important values and avoid actions that threaten their values [33,106,109]. Specifically, the stronger their altruistic (caring about others) and, especially, biospheric (caring about the environment) values, the more likely people are to engage in low-carbon actions and/or support respective policies, technologies, and system changes, probably because these actions are typically associated with social and environmental gains. In contrast, strong egoistic values (caring about personal resources) and hedonic (caring about pleasure and comfort) values typically inhibit low-carbon actions, probably because such actions are oftentimes somewhat costly (e.g., in terms of money, time, Table 1 Examples of behaviours that can (significantly) contribute to achieving net-zero energy systems [27,28,35,43,55,57,74,114] Reduce waste, share products and services (e.g., food sharing, community cooking, car-pooling, car-sharing, co-housing), refurbish products, choose second-hand products, adopt multi-purpose appliances that enable provision of more services with less resources, recycle materials. Citizenship behaviour Support low/zero-carbon actions through civic channels (e.g., product choice, voting, protesting). Note. Behaviours with relatively high carbon-reduction potential are marked in bold.
*Decarbonisation potential of alternative fuels varies due to possible side-effects, such as land use for biofuel crops. **Except when growing local products (e.g., in greenhouses) takes more energy than shipping products from elsewhere. inconvenience) [34,108,109]. Yet, some low-carbon actions may have positive implications for egoistic and hedonic values, such as eventual financial savings from household energy investments, increased comfort from home insulation, and less polluted air due to phasing out fossil fuel vehicles, which could motivate the relevant low-carbon actions. Hence, net-zero systems could have positive or negative implications for people's important values, which will guide people's behaviour, depending on how strongly they endorse those values (see Figure 2). Biospheric values provide a solid basis for many different low-carbon behaviours implied in net-zero energy systems. Noteworthy, many people strongly endorse biospheric values [18], which suggests there is a strong value base for consistent low-carbon behaviour in society. Biospheric values mostly affect behaviour indirectly: strong biospheric values strengthen people's pro-environmental self-identify, reflecting the extent to which people see themselves as someone who acts pro-environmentally, which in turn motivates engagement in many different pro-environmental behaviours, over and again, and across different situations, as people are motivated to act consistently with how they see themselves [10,79,88,118,119]. Yet, environmental self-identity is not only rooted in people's biospheric values, but is also strengthened when people realise they have engaged in pro-environmental actions [121]. Hence, reminding people of their low-carbon actions could strengthen individuals' motivation to engage in such actions consistently, and over and again in the future [120].
People do not always act upon their biospheric values. One reason may be that contextual barriers (e.g., high costs, extreme difficulty) make such actions rather unattractive or even not feasible, and engagement in such actions might threaten fulfilment of other values that are also important to people. Reducing or removing such barriers could enable people to act upon their biospheric values and promote low-carbon behaviour. Indeed, people are more likely to act upon their biospheric values when behavioural costs are lower rather than higher and when the behaviour is not strongly constrained by contextual factors [110].
When removing barriers for behaviour, it seems important to (also) target environmental values, in order to promote consistent low-carbon behaviours. For example, making the environmental consequences of behaviours salient (e.g., via green labels, sustainable product design) could make biospheric values salient an motivate people to act upon these values [44,50]. Whereas making other consequences of behaviours salient (e.g., cost reduction) might make people focus less on their biospheric values, reducing the chances that people engage in low-carbon behaviours consistently [3, 14, 38, [93].
While this Perspective focuses on the actions of individuals and households, low-carbon behaviour of organisations, including subnational governments (e.g., provincial governments, cities, towns, counties), national governments, businesses, and civic organisations, has a large emission reduction potential as well [54,114]. Organisations can contribute to net-zero energy systems by decarbonising their daily operations (e.g., reduced energy use in offices), setting more stringent carbon targets for their suppliers, introducing and developing new low-carbon products and services for their clients, and influencing policy makers to pass laws that remove barriers for low-carbon actions [134]. The latter actions can be particularly impactful if targeted at the most carbon-intensivebut also very hard to decarbonisesectors, such as aviation, iron, steel, and cement manufacture, freight transport, and fossil-fuel industry [28]. Corporate Environmental Responsibility (CER) is one example how companies can include low-carbon ambitions in their mission and implement strategies to achieve climate goals. Interestingly, believing that their company adheres to CER increased the likelihood that employees act pro-environmentally at work, especially those with moderate to weak biospheric values [87]. Hence, by setting and striving for low-carbon ambitions, organisations may motivate employees who may otherwise not be strongly motivated to engage in low-carbon actions. Relatedly, CEO's and political leaders could promote low-carbon actions by showing the example of engaging in such actions themselves, which people may be motivated to follow if they support the leader [135].

Acceptability of low-carbon technologies, policies, and system changes
Low-carbon actions of individuals and households may be facilitated by reminding people of their pro-environmental values and past lowcarbon behaviours, as well as by implementing technologies, polices, and energy system changes that enable and motivate people to engage in low-carbon actions. Public and political support can facilitate or inhibit the implementation of such changes. It is therefore important to understand which factors influence how acceptable different actors find low-carbon options and systems, as well as to understand broader institutional (economic, political, social) factors that can facilitate or inhibit their implementation.

Perceived costs and benefits of technologies, policies, and system changes
Perceived costs and benefits shape public acceptability of low-carbon technologies, policies, and system changes. For example, people generally associate renewable energy sources with benefits for the environment and the society at large, while fossil fuels are commonly seen as dirty, polluting, and dangerous [78]. This can explain why people generally favour energy production from renewable sources [107] to fossil fuels [20,51,126]. At the same time, however, people may associate the actual implementation of renewable energy projects with various costs and risks, such as negative visual impact, noise, and shadow flicker from wind turbines [82], seismic disruptions from geothermal power plants [126], loss of landscape and sense of place [32], intermittent energy supply [101], land dispossession, and negative impacts on local ecosystems [115]. This could explain why, despite relatively high public support for renewables in general, local renewable energy projects frequently face public resistance [82,115]. Addressing people's prominent concerns could increase public acceptability. For example, placing wind parks in industrial areas may be more acceptable than placing them in natural areas [131,132].
While net-zero systems are aimed at reducing carbon emissions and combating climate change, people may question the actual sustainability and mitigation potential of some elements of these systems. For example, carbon capture and storage (CCS) evokes public concerns about the risks of leakage and explosion, and is seen as an end-of-pipe solution that leaves the root of the problemcarbon emissions from fossil fuelsintact [63]. Similarly, carbon dioxide removal technologies (i.e., bioenergy with carbon capture and storage, direct air capture, and terrestrial enhanced rock weathering) were evaluated by citizens in the US and UK as not addressing the root causes of climate change and as "non-transitions" that lower the drive to cut carbon emissions [26]. Moreover, biofuels are generally seen as less environmentally friendly than solar and wind energy. In fact, in a study in Greece, only about half of participants thought that biofuels can be an effective solution against climatic changes [89]. People tend to not see biofuels as a renewable energy source [129], possibly because they associate the burning process with fossil fuels [21]. Moreover, public concerns arise about competition with other sustainability goals, such as food security, preservation of ecosystems, and land use by local communities [55]. Such low environmental and societal benefits (or environmental and societal risks) may decrease public acceptability. Or, it may result in what has been coined as "reluctant acceptance" -accepting certain elements only because there is not a better solution at the moment, but not as a solid and definite solution [13].
People may not be familiar with some of the technologies proposed for net-zero systems. For example, people had rather neutral associations with hydrogen fuels (e.g., "fuel", "part of water") and many answered "No opinion" or "Don't know" to questions about their opinion about hydrogen [85]. Similarly, many people have not formed opinions about negative emission technologies. Indeed, the majority of participants in the UK, the US, and Australia reported having never heard about enhanced weathering, in particular removing carbon dioxide from the atmosphere by applying silicate materials to agricultural land [105].
Public acceptability may increase or decrease as people learn about the costs and benefits of technologies that they have not considered before [126]. In a similar vein, public acceptability may increase after a controversial project has been realised [130] if people learn about the positive effects [55,91]. Notably, people may initially overestimate the costs and risks and underestimate the benefits of new policies and system changes, and implementing trials can make people experience positive effects, thereby increasing acceptability. Conversely, public acceptability might decrease if people learn about new risks and costs, for example local air pollution and air and water use of woody biomass [126].
The above suggests that people associate different elements of netzero systems with different costs and benefits. While important insights have been reached into costs and benefits that influence public acceptability of single mitigation options (e.g., wind parks, electric vehicles), less is known about which factors influence public acceptability of full net-zero energy systems that imply trade-offs and synergies of relevant costs, risks, and benefits of various components. This concerns not only trade-offs and synergies of different supply options (e.g., renewables or fossil fuels with negative emission technologies), but also trade-offs and synergies of energy supply and demand (e.g., if not enough renewable energy capacity is installed, there might be a need for more changes in energy behaviours), and other sustainability goals (e.g., using land for food or bioenergy crops) [31,42,72]. When asked to construct their preferred low-carbon energy futures, UK participants prioritized reducing energy use over using bioenergy, nuclear energy, and CCS [31]. As noted earlier, the latter options are seen as less sustainable, which might guide people's disfavour of these elements in net-zero energy systems. Concomitantly, focus groups research in Germany revealed that people ranked energy portfolios on the basis of excluding unfavoured elements, in particular fossil fuels, CCS, and nuclear energy, and including favoured elements, in particular renewables [90]. In other words, the less an energy portfolio included fossil fuels, CCS, and nuclear energy, and the more it included renewables, the higher was the public acceptability of these portfolios [90].

Distributive fairness, procedural fairness, and trust
Public acceptability not only depends on the perceived risks, costs, and benefits of changes as such, but also on the way these are distributed [37,78,92]. For example, public resistance brought a plan to build mega hydro energy damns in Patagonia, Chile, to a halt, as the project implied that local communities would mostly face negative consequences (e.g., flooded agricultural land, natural landscape interrupted by high-voltage power lines), while the benefitsaffordable clean energywould mostly go to the country's capital, Santiago, and the mining industry [97]. Inequalities may also rise between those who can or cannot afford low-carbon technology [71], which could fuel public resistance, especially among the disadvantaged groups. Importantly, people may not only consider whether they themselves are worse or better off than before (i.e. intrapersonal fairness), but also whether some groups are better or worse off than others (i.e. interpersonal fairness), and whether future generations and the environment would be affected disproportionately (i.e. intergenerational fairness) [92]. Providing compensations to those negatively affected may decrease fairness concerns and increase acceptability. However, compensations are not always effective and may even be perceived as bribes, fuelling resistance [22,78]. Furthermore, people may consider it unfair if only households have to change their behaviours in net-zero systems while organisations would be unaffected, which could explain why greening businesses (e.g., "stellar improvements in energy efficiency") was among the most preferred options for energy futures among UK participants [4].
Further, energy policy and energy systems changes are more acceptable when decision-making procedures are perceived as fair [39,68]. People are typically more positive about decision making and its outcomes when citizens [6,53,127] or civil society organisations can participate in the decision making [11,12]. In contrast, people tend to resist decisions when they feel that there is a lack of transparent information, that they have been involved too little and too late, that marginalized groups have been excluded from decision making, and when they see the decision making as a violation of human rights (e.g., indigenous rights) [25,46,115]. People particularly want to be involved in decisions that concern their direct environment (e.g., renewable energy siting nearby), rather than more general (e.g., national) climate policies [77]. This can be problematic for net-zero energy systems, as many decisions regarding the technology and system changes are taken early in the decision-making chain (e.g., (inter)national climate policies), which subsequently guide how concrete projects in specific locations take shape. Only being able to participate in decision making on concrete projects, while not being able to influence major decisions, may be experienced as fake participation and fuel public resistance [25,46,83,116]. Participation upstream in the decision-making chain could prevent that people are faced with the decisions already taken, yet policies at this level are highly abstract and uncertain, which might reduce people's motivation to participate. Initial evidence suggests that explicating the possible consequences of future energy scenarios for people's core values, such as the impacts on economy, employment, and personal finances (egoistic values), on local and global environmental quality (biospheric values), on everyday comfort and quality of life (hedonic values), and on social justice and democracy (altruistic values), could motivate people to participate, even in decision making on general energy policies [30,61,80]. Yet, people may not want to participate in decision making always and about everything [9,56]; more research is needed into whether, when, and how people want to engage in decision making on net-zero energy systems.
Furthermore, people are more likely to accept low-carbon policies and system changes if they trust responsible actors, as found for, among others, wind energy projects [41] and solar energy projects [66]. Interestingly, public participation in decision making had less added value to project acceptability when people trusted the responsible party, suggesting that acceptability can be increased by either letting people influence major decisions or having trustworthy parties to take the decisions [66]. While companies and governments often emphasise that they have the relevant knowledge and expertise (i.e. competence-based trust), acceptability is alsoand sometimes even moreinfluenced by how much people think that responsible actors have good intentions and take public concerns into account (i.e. integrity-based trust) [67,96]. Besides trust in responsible actors, trust in the functioning of net-zero energy systems (e.g., trust in automation that may "decide" how much energy from which sources is used when) is important for acceptability, including trust that these systems will function properly, as well as that people's privacy and autonomy will be respected [16].

Institutional acceptability
Factors related to political, economic, and social structures and the particular innovation systems surrounding renewable energy technologies and supply chains, can facilitate or hinder the implementation of low-carbon technologies, policies, and system changes. Notably, renewable resource endowments, manufacturing capacity, and a history of investment in energy research do not sufficiently account for why countries such as Germany and the United States have successfully (or unsuccessfully) supported wind and solar systems [58,64]. Rather, Germany's strong support for renewables has been pushed by institutional factors, such as an election system based on proportional representation that enhances access to small and medium enterprises and community groups, and the institutional discrediting of nuclear power by a strong social movement coupled with relatively strong concern about climate change. Additional factors include European Union constraints on subsidies for coal and the ability for renewable energy industries to offset high rates of unemployment in Eastern Germany. By contrast, a political system easily captured by fossil-fuel lobbyists with no sustained support for a green or environmental party, lack of leadership on climate change, profligate subsidies for coal, and strong opposition from energy companies impeded institutional efforts in the United States to pass national renewable energy legislation [58,64].
Conflicts between countries may inhibit a transition to net-zero energy systems, for example countries that depend on fossil fuel revenues or promote regimes that subsidize fossil fuels versus countries that subsidize renewables or nuclear power [84,104]. More research is needed to map out such conflicts and identify ways for conflict resolution, such as distributing costs and benefits of energy transitions across countries in a fair way. These themes imply that issues of distribution and fairness reverberate at the institutional and country level as well. Relatedly, certain solutions, such as offshore wind energy developments, have implications for multiple countries, which raises the question what new (international) governance structures, justice or fairness norms, and legal regulations may be required.
An analysis of why a set of 18 countries adopted different types of renewable policy mechanisms revealed that "pro-renewable" cultures could largely be explained by political and cultural styles of regulation, the importance of energy security as a policy issue, and the absence of a strong fossil-fuel energy industry [48]. Countries with a market-oriented culture and liberalistic government often choose market-based incentives that integrate well with energy markets and regulatory structures and offered premium incentives for investors in renewable energy. Countries with mass publics concerned about energy security and/or climate change issues were more likely to embrace renewable energy, especially countries that had "meager" domestic resources of coal and oil. The absence of a strong conventional energy industry and lack of major manufacturing capabilities in fossil and nuclear power are associated with countries more strongly supporting renewable energy industry [48].
Politicians may be reluctant to implement policies and system changes when they believe that the public would strongly oppose them. Hence, it is critical to understand whether policy makers' perceptions of public support are accurate, and which factors influence their perceptions of public support. This is particularly important as politicians may underestimate how strongly people endorse biospheric values [18] and overestimate the degree of public denial of anthropocentric climate change [107]. At the same time, the public may actively demand politicians to adopt more (stringent) low-carbon policies, as in the case of an increasing number of climate protests [70]. Besides the general public, other key stakeholders may have concerns and oppose low-carbon technologies, polices, and system changes. For instance, landowners may fear drop in property values because of wind parks, environmentalists may worry about the effects of bio-crops on local ecosystems and the need to use fossil fuels to "backup" intermittent energy supply from renewables, and project developers may be discouraged by anticipated public resistance [100]. As such, opposition merges together community, environmental, economic, and political concerns [100]. Future work could explore whether similar or different factors influence acceptability of energy technologies, policies, and system changes among various actors, including micro-level factors (e.g., perceived costs and benefits) as well as macro-level institutional arrangements, including cultural, economic, geographic, historical, political, and social structures where net-zero pathways are embedded [5,59]. Next, it is critical to understand the role of meso-scale actors and interactions in the transition to net-zero systems, such as corporate behaviour and regional, local, and civic governance, and climate movements and counter movements [36]. Furthermore, future studies could explore interactions between micro, meso, and macro levels in transitioning to net-zero systems. For example, meso-and macro-level institutional arrangements can either constrain or enable low-carbon actions of individuals and households, while individuals and households can in turn influence low-carbon behaviours of businesses, organisations, and governments via citizenship behaviours (e.g., choosing products based on their carbon footprint, voting for political parties based on their environmental and energy agendas).

Culture and regional differences
Net-zero energy systems may involve different configurations in different parts of the world, with no single best solution. For example, local climate, including solar insolation, and availability of architecturally suitable roof surfaces can make solar PV's more feasible in some regions than others [23]. Also, some technologies are only feasible in some regions (e.g., hydro-energy dams), and the risks of technologies may be specific to the regions and their national heritage in which they are installed (e.g., destroying pristine nature, resettling indigenous communities) [125]. Besides the feasibility of technology, cultures and regions differ in their institutional structures, including their dependency on fossil fuels for the economy and the primary energy supply, the degree of state involvement, and whether they are globalist-focusing or isolationist [111]. These diverse but coherent variables give rise to distinct national energy cultures and varying low-carbon ambitions [111], as illustrated in Table 2.
Not all regions can be expected to reduce their energy demand equally. Indeed, energy demand in the global south is expected to increase and it is generally agreed that this needs to be accommodated as many people face energy poverty in this region [86].
Highly industrialised and developed countries can potentially learn from the developing world, for example to appreciate how the transition from centralised fossil energy systems to many small and highly diverse decentralised energy facilities could be supported. Notably, developing countries already mostly have small scale and highly diversified energy systems, and institutional arrangements for governing and coordinating it. Their experiences may yield important lessons for countries that still mostly rely on centralised energy systems, and reveal how to implement and support decentralised renewable energy systems, and which governance regimes can support relevant changes.

Design principles for net-zero energy systems and concluding remarks
In this Perspective, we showed that human dimensions are inherent to the transition to net-zero energy systems. Social sciences research has provided a solid basis for design principles to encourage people's lowcarbon behaviours [110] and the acceptability of carbon-reduction programmes and policies [113], which has provided key insights into how to the design, develop, implement, and operate net-zero energy systems (see Table 3). First, change actors need to consider how to motivate and empower individuals and households to engage in low-carbon behaviours, ideally focusing on behaviour with highest carbon reduction potentials in net-zero systems. Relying on technology development alone is not enough, as technological solutions will only be effective if adopted and used by the public. Moreover, technological Table 2 Examples of four varying national energy cultures (based on [111] Table 3 Design principles for understanding and addressing the human dimensions of net-zero systems (based on [110,113] ○ There is no one-fits-all solution: take regional and cultural aspects into account Incorporate the social sciences early ○ The social sciences provide critical insights into how to develop technologies, policies, and system changes that are acceptable and get adopted by the public ○ Incorporating the social sciences early in the design process prevents public resistance towards the already-made, topdown implemented technologies, policies, and system changes solutions typically are more efficient when accompanied by behavioural change, such as matching the energy demand to the energy supply from renewable sources. Second, only providing people with information is often not enough to change behaviour, as people are not likely to change their behaviour when they are not motivated to engage in low-carbon actions. While individual costs may hinder or enable people to engage in such actions, other motives too need to be considered. Particularly factors that strengthen people's intrinsic motivation to act pro-environmentally (e.g., their motivation to save the environment and/or concerns about others) can result in people engaging consistently in many and different low-carbon actions needed for net-zero systems. Third, policies and system changes aimed at low-carbon behaviours and technologies need to be acceptable to the public. Again, not only immediate, individual costs and benefits, but also the effects of technologies, policies, and system changes on the environment and other sustainability goals (e.g., food security, land use by local communities, local ecosystems) influence public acceptability. Next, people not only consider the costs and benefits as such, but also the extent to which these cost and benefits are fairly distributed, the extent to which fair decision-making procedures have been followed, and whether responsible actors can be trusted. Importantly, there is no universal best net-zero solution, and therefore cultural and regional aspects need to be considered when designing, implementing, and managing net-zero systems. These design principles informed by the social sciences will be most effective if incorporated from the very beginning of developing net-zero systems, rather than at the end when the decisions are already made and people need to be convinced to adopt the proposed options and change their behaviour accordingly. Specifically, if the solutions are already pre-baked, without incorporating public concerns and interests from the start, they may be perceived as threatening (rather than supporting) people's values and people may feel excluded from the decision making, which might fuel resistance.
Admittedly, it is important to emphasize that the overwhelming bulk of our evidence in this Perspective is from studies in "WEIRD" capitalist nations, that is those that are western, educated, industrialized, rich, and democratic [52]. So, one must be cautious about overgeneralizing and also work harder to engage different countries and cultures in both research and in design of programs and policies for moving to net-zero systems. Different sorts of inquiries may be relevant in different countries and cultures. For example, the focus in developing countries might need to be on setting up energy systems or increasing affordable access to energy services, and not necessarily on changing the existing systems or reducing carbon emissions. Furthermore, in order to transition to inclusive net-zero energy systems, it is important to understand and address the needs of specific groups, such as members of minorities or disadvantaged communities, which have been scarcely addressed in research, with some exceptions (e.g., [111]).
To conclude, the inherently social matters of net-zero energy systems demand that the design, implementation, and operation of such systems grapple better with factors that influence low-carbon behaviours and acceptability of low-carbon technologies, policies, and system changes, and the role that cultural and regional differentiation can exert on lowcarbon actions globally. Although the natural and physical sciences clearly have much to offer, each of these three themes of behaviour, policy, and culture demand a more refined, comprehensive, and early engagement with the social sciences, in order to achieve net-zero energy systems that enable, motivate, and support low-carbon actions.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.