Determinants of Decarbonization—How to Realize Sustainable and Low Carbon Cities?

: The objective of this paper is to identify the determinants of decarbonization processes in Poland by urban and rural areas. It also presents directions for knowledge diffusion on decarbonization to develop a sustainable energy strategy for Poland, particularly for local governments and cities. Despite extensive research on the determinants of decarbonization and sustainable energy development, there is a lack of speciﬁc solutions in this area. The authors of this paper investigated which determinants, according to the respondents, would lead to better decarbonization solutions in cities and villages in terms of sustainability. The studied sample was purposefully selected and an online questionnaire was used with the use of the “snowball” method. The authors conducted surveys that allowed the concerned parties themselves (respondents) to indicate which factors they believe best inﬂuence decarbonization. Such measures are helpful in terms of the understanding public acceptance of decarbonization in terms of the energy transition. This is of particular importance in terms of green governance globally and in Europe. The results of the authors’ research indicate that despite the reduction in the share of coal in residential and domestic heating, coal remains the main source of electricity generation and that the potential for low-carbon policy to have an impact on solving urban challenges is underestimated. From the ﬁndings, it can be concluded that more in-depth research is needed on public acceptance of decarbonization in its broadest sense and its implications.


Introduction
One of the most essential sources of decarbonization processes is the concept of sustainable development [1,2]. Thanks to the concept of sustainable development, a number of international, national and local economic solutions have been implemented [3,4]. The development of this concept and its growing importance has led to, among others: United Nations General Assembly Resolution of 21 October 2015 (hereinafter: Resolution), which provides the impetus for many processes, including those closely related to decarbonization and its determinants [5,6].
The move towards sustainable and low-carbon cities is one of the responses to climate change. It fits, through several concrete actions, into the concept of smart cities. This concept is given a lot of importance, pointing out that smart cities are becoming the center of innovative solutions and thus of economic growth, and therefore require proper analysis and consideration [23]. The discussion and research conducted within the smart cities concept framework gain its justification, especially since the idea involves some risks. An example of the risk of adverse consequences of the implementation of some innovations is the achievement of too high energy efficiency of buildings, which in turn would increase the price of energy distribution in the network [24].
Particularly developed smart city concepts are implemented in Masdar (Abu Dhabi), Stockholm (Sweden), Amsterdam (The Netherlands) or Yokohama (Japan) [25]. Among the many solutions, the implementation of which fits into the assumptions of smart cities, the literature mainly indicates innovations in energy technologies [26], transport [27], construction or creation of green building standards [28,29]. Examples of innovations that are analyzed in terms of efficiency, cost-effectiveness or functionality are passive house heating and lighting systems [30,31], national integration of renewable energy system in cities [32] or optimization of road lighting to improve energy efficiency [33]. Besides, also noteworthy is the concept of using urban greenery to create a microclimate suitable for residents, which results not only in lowering the temperature but also has an impact on air purification [34]. From the point of view of the research conducted in this paper, it is also important to point out the measures discussed in the literature in the field of home heating systems using heat pumps and underground ventilation systems [35].
As indicated above, the literature does not explicitly address the social determinants of decarbonization processes. However, other discussed criteria, such as economic or technological criteria, can be identified [36,37].
Comparative analyses to compare the cost-effectiveness of specific mechanisms, as seen in the example of the installation of light-emitting diode (LED) lighting in cities [23]. The value of economic determinant is also visible in literature as a condition of implementing or expanding new renewable energy sources such as hydropower [38]. In addition, it should be noted that the economic determinant is the potential creation of business opportunities [39,40] associated with applied measures aimed at decarbonization or smart cities [41,42].
The technological criterion is related to the development of modern technologies, including information technologies, aimed at supporting the automation of smart city creation processes [43,44]. The number of types of smart cities concepts depends on the number and type of existing technologies [36,45]. The described criterion has a unique character because its application is related to the specific technological development of the city where it is to be applied; however, in case of insufficient development, some activities cannot be applied [46][47][48]. Examples of measures can be the implementation of intelligent transport or intelligent traffic management. The aspect of new technologies is particularly evident in the implementation of intelligent traffic management, which in its assumptions uses a number of devices, such as roadside sensors or active signaling, to improve traffic flow or reduce the arrival time for traffic participants [49,50]. It is worth noting that the technical criteria also propose solutions that are based on advanced planning and do not require advanced technologies at the time of implementation. An example of such measures is the natural cooling of urban environments, which increasingly becomes the focus of planners and designers [51,52].
The economic criterion is considered in the form of sustainable and low-carbon cities, are a frequent subject of scientific analysis. One of the possible reasons for this phenomenon is the distribution of the population in urban areas. Using the example of the European Union, it can be pointed out that as many as 68% of the people resident in the Member States live in urban areas [43]. In addition, these areas are responsible for 70% of the primary energy consumption, which translates into 75% of the total greenhouse gas emissions in the European Union [53,54]. Globally, 3% of the land area is urbanized, and more than half of the population lives in urbanized areas. These areas are responsible for 70% of CO 2 emissions [55].
A concept that can not only support the decarbonization process but also complement it by supporting the smart cities idea is the notion of the energy prosumer. The first attempts at defining this concept assumed that consumers [56,57] produce more goods and services for their own consumption [58]. Today, the literature assumes that an energy prosumer is a person who both produces and consumes energy [59] or a person who actively manages the production of their own energy and their own consumption of that energy [60]. Prosumers not only increase opportunities to generate clean energy but also support the technological development they need to meet their needs. Additionally, they can take an active role in regulating energy demand, thereby influencing the energy market [61,62].
Adding the aspect of society to the decarbonization process directly or indirectly by supporting other methods that implement decarbonization processes will allow the creation of a model of citizen energy [63].
Increasing the role of prosumers and their participation in the decarbonization process is associated with the development of energy justice theory. According to this theory, we can talk about principles that should form the basis for decision-making processes. These include good governance, easy availability and sustainability [64]. States, guided by the theory of energy justice, can support the development of prosumers by, for example: supporting less wealthy consumers and enabling them to become prosumers or by supporting renewable energy initiatives by influencing its availability [61].
Importantly, the statistics indicated above may change due to the increasing rate of urbanization in the 21st century, which is rooted in the rising world population and the migration of people to urban centers [24]. According to World Bank projections, the urban population will double by 2030, assuming current economic growth [65,66]. These figures alone should be enough incentive for urban centers to take a greater interest in ways to address the challenges of a growing population, which include adequate living resources and air pollution, among others. These global challenges require drastic measures; in other words, the most critical actions of the 21st century [24].

Climate Change Perspective
According to the authors of the paper, in addition to the growing population of cities, attention should be paid to the issue of climate change and its impact on cities. Among the frequently cited effects of climate warming on cities are rising urban temperatures and rising sea levels [24]. According to one study, there is a risk that more than 1.5 billion people living in cities will be exposed to temperatures above 35 • C for three months by 2100, compared to 5.6 million today, which is a real threat to urban populations [67]. Regarding sea and ocean level rise, it is essential to note that more than 146 million people live in areas 1 m above sea level. In contrast, 397 million people live between 1 m and 10 m above sea level [68]. The currently predicted sea-level rise oscillates between 0.5 m and 1 m by the year 2100. There is a risk that if certain events occur, such as the melting of the Greenland ice sheet or West Antarctica, the water level could rise by up to 7 m [69]. The effects of rising sea and ocean levels could significantly affect the functioning of major metropolises such as New York, Mumbai, Dhaka, Tokyo, Lagos, Cairo or Rio de Janeiro. Moreover, these effects are already visible and manifested in the form of storms, floods, and heavy rains, which were almost four times more frequent between 2003 and 2013 than between 1901 and 1910 [70].
In addition to the determinants [71][72][73], the decarbonization process itself is also associated with concerns arising from its implementation. These concerns range from efforts to shut down some existing fossil fuel-based industries [74,75] to concerns about renewable energy sources and their intermittent supply [76][77][78].

Methods
This study addresses the scientific problem of decarbonization and changes in diffusion in the practice of that process and attempts to find a solution to it. Schmidt and Weight go on to note that within the broader energy sciences, interdisciplinary work remains rare: "despite the predominately socioeconomic nature of energy demand, such interdisciplinary viewpoints-albeit on the rise-are still the minority within energy-related research" [79]. Therefore, the authors made an attempt to conduct such research.
In the literature on decarbonization processes, particularly regarding their social understanding, there are no broad theoretical explanations indicating the crucial determinants supporting such processes [36,79]. Furthermore, even though decarbonization has been discussed in both European Union and international literature, there is no reference to knowledge diffusion processes as the causative factors for those changes precisely in the scope of rural and urban areas [80].
To determine the current state of knowledge and to identify specific existing research gaps, the authors have compiled the literature on the subject, taking into account the compilation and integration of existing studies. This evidence is conducted as a systematic literature review.
The structured questionnaire was performed with a sample of respondents from a relevant target population. The design of the research tool was based on already standardized and verified tools. The research was based on a survey by the Tyndall Centre for Climate Research [81]. The survey asked two questions with responses based on the Likert scale. The questions concern fundamental issues on the determinants supporting decarbonization processes in Poland-urban and rural areas and the model of decarbonization (centralism vs. localism).
The authors used the questionnaire as a method widely used in the practice of survey research. The studied sample was purposefully selected and an online questionnaire was used with the use of the "snowball" method.
The research was conducted between December 2019 and April 2020. This research included 444 respondents who filled in the questionnaire online, of which 46% were men and 54% were women. This brings the minimum sample size to 384, for the whole population of 38 million people in Poland. The following assumptions were made for statistical research.
The individual activities indicated in the survey are assigned one of the following grades:
Significant impact.
The survey also asked two open questions on the most effective solutions to support decarbonization processes in rural and urban areas. Question-"What do you think the EU should introduce solutions, regulations regarding decarbonization?"-concerns what solutions the EU should introduce in decarbonization. The respondent could give a free, subjective answer or several answers. Our intention when asking open questions was to obtain as many attitudes and opinions as possible to analyze the studied phenomenon, including decarbonization. The second open question: "What do you think should be the main factor in the decarbonization process in Poland?" The research was exploratory, conducted to determine the nature of the problem, and was not intended to provide conclusive evidence but to obtain a better understanding of the problem [82].
The sampling was focused on respondents dealing with the problem of decarbonization. Among the respondents, the majority were people living in the cities. Table 1 presents the structure of the sample. The research was conducted on a representative sample. Source: Own research based on the results of an online survey, n = 444 (444 respondents who filled in the questionnaire online, of which 205 were men and 239 were women).

Research
The research yields answers for the following research question: "Which of the following do you think has the most impact on decarbonization?" 1.
Subsidies for mining.
Capacity market.

5.
Opening the EU energy market.
Additionally, the second question: "Which of the following activities should be transferred from central to local?"
Compensation for electricity, energy storage, production 4.
Funds for environmental protection 5.
Support of development of modern power sources-cities.
The answers to the questions are based on Figures 1 and 2.  The answers provided by the respondents show that they care most about local programs aimed directly at interested residents. Both town and village residents agree that direct support programs can best and most effectively lead to an effective decarbonization process. Photovoltaic support programs were also assessed as effective at an equally high level. These programs also provide direct support [79]. Thus, the inhabitants of villages and cities choose direct support programs that will reach recipients and, therefore, will be an incentive to replace stoves or install photovoltaics. To a small extent, rural residents are much more concerned with these programs, but this is natural. Rural residents can benefit more from these programs as this is only possible in the suburbs in the main program [81]. On the other hand, city dwellers also strongly believe in the effectiveness and efficiency of these direct programs. There are also solutions on the market that can meet their expectations. Housing cooperatives and communities cooperate with energy and photovoltaic suppliers to install group installations in cities, securing multifamily buildings' needs.
The data from Table 2 are presented in Figure 3. They are the means of all responses obtained in the studies.   The next question and the answers to it confirm that local support is much more appreciated and much better perceived as effective and efficient in the decarbonization process. Here, as well, to a small extent, rural residents are much more concerned with these programs, but this is natural. It is worth noting that villagers can benefit to a greater extent from these programs, especially local ones, which have independent housing and often burn solid fuels. the responses given by city dwellers show slightly lower response scores, as this is only possible in the suburbs of cities. In both question one and question two, city dwellers also firmly believe in the effectiveness and efficiency of these direct programs. In the second question, again, photovoltaics takes a key place. It should be noted here that solutions that can meet the expectations of city dwellers are also more and more distressed. There are still no specific legal regulations, but housing cooperatives and communities cooperate with energy and photovoltaic suppliers to install group installations in cities, also securing the needs of multifamily buildings, precisely speaking of the needs of shared spaces in buildings, but also already providing green energy to individual residents or lighting (presented at Table 3 and Figure 4).    Figure 5 presents the means obtained from the answers about the importance of impact on decarbonization and standard deviations. They clearly show that all standard deviations are in the range from 1.5 to 2.6. The most unambiguous answers of cities respondents concern the installation of photovoltaics. Both the inhabitants of villages and cities gave the highest answers (according to the average) to the answer n1, i.e., "Necessity to transfer actions from the central to the local level: subsidies for the residents/end users (i.e., boilers' replacement program)". The data from Table 4 are presented in Figure 6. Figure 6 shows the average levels of answers to the question necessary to transfer actions from the central to the local level and the standard deviations for it. Priority is given to local support programs in the field of boiler replacement and programs related to photovoltaics. Table 4. Mean values in responses to the question "Necessity 1 to 5", sorted by place of residence.   The chi-squared tests for cities and villages are presented Table 5. The results of the importance of impact on decarbonization survey were tested with the chi-squared test, which showed that there is a strong dependency between all the responses. For the "city" category the calculated chi-squared result is 421.8, whereas for the "village" category, the chi-squared result is 156.9. The p-value in both these cases is <0.000001, and the result is significant at p < 0.05. The chi-test for necessity to transfer actions from the central to local level shows similar results.

Place of Residence
The survey also asked two open questions on the most effective solutions to support decarbonization processes in rural and urban areas. Question-"What do you think the EU should introduce solutions, regulations regarding decarbonization?"-and the second open question: "What do you think should be the main factor in the decarbonization process in Poland?".
Both questions are open questions to which the respondent could give a free, subjective answer or several answers simultaneously. The authors' intention when asking open questions was to obtain as many consumer opinions as possible, which will shed a new, different light on the examined phenomenon of the decarbonization process-how to realize sustainable and low carbon cities. It should be stressed that decarbonization is still a phenomenon that is poorly recognized in society, as is expressed: (1) Among the 444 respondents, 238 respondents answered question 11 (nearly 54%) and 249 answered question 12 (which constituted 56%). (2) In both open questions, only 80% of the respondents who answered the abovementioned open questions proposed interesting suggestions, while nearly 20% of the survey participants indicated that: "has no opinion"; "cannot evaluate"; "does not know"; "difficult to evaluate". (3) From this sample, the authors chose only those answers that are consistent with the decarbonization process and the implementation of a sustainable and low-carbon city, as the local perspective (of the cities) is closer to the surveyed sample of respondents.
Respondents' answers to the question "What do you think the EU should introduce solutions, decarbonization regulations" have been categorized into five basic groups (categories) and presented in Tables 6 and 7 refers to the Sustainable Development Goals (SDGs) and indicates which respondents carried out this activity (living in a village or city). This table (Table 6) presents the responses of individual survey participants, treating them as a determinant of sustainable development objectives in the context of the division into town and village, namely: Action Items: Table 6. List of answers for two questions.  Table 7. EU solutions for decarbonization determinants from the SDG perspective (sustainable and low carbon cities)implementation proposals.

N.B.
Title of the Action Target Name According to SDG (GOAL's 1-17)

2.
Nuclear energy Climate action (GOAL 13) Sustainable cities and communities (GOAL 11) Innovation and infrastructure (GOAL 9) Renewable Energy (GOAL 7)  Table 7 presents the EU solutions for decarbonization determinants from the SDG perspective (sustainable and low carbon cities) for implementation proposals.
Respondents also drew attention to issues related to the low carbonization of cities in the context of the decarbonization process, such as To sum up, although the decarbonization process assessments were based on the respondents' subjective opinions, it should be noted that the views and attitudes of the external environment, in this case consumers, are fundamental. This is true in a situation where the most appropriate solutions related to climate change and zero-emissions are being sought in the international arena, due to their harmfulness to the environment.
Considering the results of the assessment of the main factors influencing the decarbonization process in Poland, the respondents were asked in the next open question: "What do you think should be the main factor in the decarbonization process in Poland?" The possible answers were categorized according to four basic groups (categories) and shown in Figure 7, which refers to Sustainable Development Goals (SDG). This figure shows the answers to individual survey participants, treating them as a determinant of sustainable development goals for cities and villages. In the respondents' answers, the main factors in the decarbonization process are subsidies and nuclear energy (approx. 50% of the respondents), followed by the conversion of coal-fired power plants to nuclear and decommissioning of old solid fuel boilers. The most frequently indicated decarbonization determinants-how to realize sustainable and low carbon cities-are presented in Figure 7. In the opinion of the respondents, there were statements which put forward specific conclusions about the key determinants in the decarbonization process in Poland, that is, above all, education, knowledge and awareness of the society and enterprises for the sake of the future, clean air, and health. These are also factors such as the use of RES, subsidies for RES, replacement of boilers, development of new technologies (including transmission infrastructure) and change of deep-rooted "people's beliefs".
The group of respondents surveyed is aware that the issue of reducing fossil fuel combustion and carbon dioxide emissions does not have a single, simple solution. The largest sources of carbon dioxide emissions are the burning of fossil fuels in power stations, car and aircraft transport, processes related to the production of industrial goods and deforestation.

Result Discussion
Decarbonization is influenced by the following conditions: subsidies for mining, subsidies for local governments (e.g., decommissioning of boilers), prosumer solar photovoltaic development programs, the power market, and the opening of the European Union energy market. The authors were interested in social support for these conditions. The research showed that subsidies for the mining industry did not affect the decarbonization process. The respondents stated that development programs for prosumer solar photovoltaics had a significant or reasonably large impact on the elimination of CO 2 emissions due to their harmfulness to the environment. Regarding the most important local programs for urban residents, both urban and rural residents agree that direct support programs can best and most effectively lead to an effective decarbonization process. Photovoltaic support programs have also been assessed as useful at an equally high level. These programs also provide direct support. Therefore, rural and urban residents choose direct support programs that will reach their recipients and thus encourage the replacement of boilers or photovoltaic installations. The authors also examined the social assessment of the level at which support should be provided. It is undisputed that local programs are more effective than state programs, and they are seen as more effective. It is necessary to point out that the respondents themselves pointed out that such deterrents as the introduction of emission limits for households, the lack of administrative formalities and the introduction of additional charges for "polluters", which play an ongoing role in the decarbonization process. Given that urban emissions are responsible for approximately 70% of greenhouse gas emissions, it is reasonable to assume that the pursuit of carbon neutrality, and any actions related to and aimed at it, without the participation of the urban sector, is doomed to failure. However, it should be pointed out that the amount of costs associated with going green, is significant.
The importance of the role of the urban sector can be seen in the analysis of the EU Green Deal, which aims to achieve climate neutrality by 2050, superimposing the essential elements of this agenda on a pyramid scheme. At the top of the pyramid is the goal of climate neutrality, going downwards, the next step is its approval by the executive of the Member States, and then, the result of the work is passed on to the state bodies of each Member State, ending with the municipalities, which thus form the basis of the whole program.
To quote an excerpt from a speech by Katarzyna Szumlewicz, Programme Manager at the European Commission's Directorate-General for Regional and Urban Policies, in a discussion on ways by which cities can reduce their carbon footprint: "Cities face all kinds of challenges. They are seen as opportunities but they are also seen as those who have to take the responsibility for driving climate neutrality".
The cost for cities globally to achieve climate neutrality is estimated to be in the range of USD 1.8 trillion annually, according to a report by the Coalition for Urban Transition. The report indicates, however, that these costs can be considered a form of investment with a return calculated at USD 2.8 trillion by 2030, and up to USD 7 trillion by 2050. The indicated increase is due only to cost savings. It is estimated that by 2050 more than 70% of the world's population will live in cities. Already today, cities account for three quarters of carbon emissions worldwide [84].
Based on the research results, their analyses lead to similar or even the same specific conclusions about the critical conditions of the decarbonization process in Poland; that is, above all, education, knowledge and awareness of society and business. This is particularly important in light of global climate change. The challenges facing cities require a fundamentally different approach to the tools best suited to ensure a stable homeostatic relationship with nature and, at the same time, sustainable development of human life in the future [85,86].

Conclusions
Currently, the largest Polish and European cities support decarbonization activities. In the case of Poland, the share of coal used to heat flats and houses is decreasing. However, coal remains the most important fuel for electricity production. Local governments and local authorities must implement environmentally friendly, cost effective and socially acceptable policies. It is not only a fashion, but also a necessity.
The conducted research is a solid basis for the following considerations. In future, researchers should look for economic confirmation of whether the government is implementing a decarbonization policy in accordance with the needs of cities' and regions' and social expectations. It is important to carry out a detailed study in the future whether Poland will implement a coherent, long-term vision of the transformation of the economy into a zero-emission economy by 2050. In the future, the authors should focus their research on areas related to social acceptability: energy efficiency in buildings, low-carbon transport in cities, and sustainable waste management. The role of low-carbon policies in addressing broader urban challenges has been greatly underestimated. The positive impacts resulting from effective mitigation can be uncertain in scale and global in nature. It should also be pointed out that the vast majority of them will be felt in the medium to long term, and the question to be asked is whether people will be aware of them and accept them. A practical perspective indicates that a bottom-up approach examines these issues in specific cities, before considering the problems of aggregating or extrapolating results at the national, regional or city level. Accordingly, policymakers with a political focus should develop a more precise, consistent, and compelling language/narrative about the co-benefits of urban partnerships. After all, people may not only see solar PV but also, for example, green hydrogen.
Cities are the largest social clusters, concentrated, well-functioning organisms, it is important that they receive proper support from the government in the area of decarbonization policy.

Conflicts of Interest:
The authors declare no conflict of interest.