Assessing the Level of Energy and Climate Sustainability in the European Union Countries in the Context of the European Green Deal Strategy and Agenda 2030

: The concept of sustainable development integrates activities in the economic, environ ‐ mental and social areas. Energy policy, which is very closely linked to climate protection, is of key importance for achieving the goals of the concept in question. All these elements are connected by the European Green Deal strategy and Agenda 2030. Their implementation requires the evaluation of previous actions undertaken within the framework of sustainable development and the diagnosis of the current state. Therefore, this article presents the results of such research in relation to the key industry connected with this process, which is the energy sector. The research methodology was based on the analysis of 14 indicators that characterize four basic areas (dimensions) related to en ‐ ergy and climate sustainability. These indicators concern energy and climate as well as social and economic issues. This approach makes it possible to comprehensively assess the actions taken so far in the implementation of sustainable economic development in the energy and climate area in the European Union (EU) countries. The entropy ‐ complex ‐ proportional ‐ assessment (COPRAS) meth ‐ odologies, which belong to the group of multiple criteria decision ‐ making methods, were used for this study. The conducted research allowed for the assessment of the changes in the EU countries in terms of energy and climate sustainability between 2009–2018. In addition, the effects of the in ‐ troduced changes in individual years and in relation to the studied areas (dimensions) were also evaluated. Based on the results, considering the adopted criteria, the EU countries were divided into groups similar to the level of energy and climate sustainability. The results constitute a valuable set of data, which allows for a wide and in ‐ depth multicriteria analysis. This allows for a very ob ‐ jective and broad assessment of the effects of sustainable development policies in the EU countries and the current state in the context of the European Green Deal strategy and Agenda 2030.


Introduction
In Europe, the concept of sustainable development is a fundamental and overarching objective, which is contained in Article 2 of the Lisbon Treaty [1]. One of the most important tasks of this concept is to ensure a stable natural environment, sustainable consumption and production, and the eradication of poverty [2,3]. The result of these actions is to ensure that all citizens have access to sources of stable, sustainable, and modern energy at affordable prices [4,5]. Sustainable energy should be understood in this context as energy that is produced and used as much as possible from renewable energy sources (RES), as it is practically emission-free and, above all, does not emit greenhouse gases A wide range of research, considering many factors from different areas and using analytical tools, makes this work both a new and original approach to the presented subject. The basis of the assessment was the performance index (Pi) of sustainable development determined on the basis of 14 indicators representing energy, climate (environmental), social, and economic dimensions. The four main dimensions of sustainable energy and climate development enabled a comprehensive assessment, including the most important elements of this development, of 27 EU countries in the period between 2009-2018. The utilitarian purpose of this research was to show the diversity of the development of individual EU countries in this area. The results show that the comprehensive energy and climate policy of the EU, in the operational scope, should consider the specificity of groups of countries and be dedicated to those with similar problems. This approach should ensure its greater effectiveness and efficiency.
The presented approach to the problem of the implementation of economic sustainability should be considered novel. The analysis of energy and climate protection has not been carried out in such a wide range, using many factors.
A number of factors can be formulated to prove the originality of this work in relation to both existing and published studies.
The first such factor is the selection of 14 indicators that characterize countries in terms of their energy and climate sustainability. These indicators characterize the key economic and social areas (dimensions) of life in these countries, namely energy, climate, social, and economic.
The second factor concerns the ranking of the EU countries in terms of energy and climate sustainability from 2009 to 2018 and the assessment of this level for each of these countries. This assessment was also made for individual studied areas (dimensions). The findings made it possible to trace the changes in these countries in each year and in the studied areas. Moreover, this approach allows a broad analysis in terms of comparing the level of development of these countries among themselves and in relation to the EU as a whole.
The third factor concerns the assessment of the level of energy and climate sustainability and the division of the EU countries into four classes in terms of this level. The basis for the division was the value of the Pi index for sustainable development. The determination of these classes (groups) creates great opportunities for cooperation between countries in these groups. This relates primarily to applying for EU funds, implementing common energy and climate policy and taking initiatives in many other areas related to activities for modern energy and climate protection.
Another (fourth) factor proving the originality of this work concerns the use of the entropy-COPRAS method to assess the level of the EU countries in terms of their sustainable energy and climate development. This method is the combination of a method used to determine the weights of indicators (entropy) and a method used for the multicriteria analysis of various types (COPRAS). The Pi index can be treated as an objective measure of sustainability level. The use of this method in the presented analysis increases its scientific value and makes the results more credible.

Sustainable Energy and Climate Development
The concept of sustainable development was presented in the UN report "Our Common Future" in 1987 [29]. This report emphasized the role of energy in achieving sustainable development. In Agenda 21, energy development is mentioned in conjunction with sustainable development in the chapter on atmosphere protection [30]. The relationship between the atmosphere, greenhouse gas emissions, and energy is also emphasized in the 1992 UN Framework Convention on Climate Change and the 1997 Kyoto Protocol. Both documents call for a new, sustainable approach to energy development with special emphasis on reducing greenhouse gas emissions [31,32]. In these documents, energy is regarded as the basis for achieving sustainable development and is linked mainly to climate issues as well as energy security and the scarcity of fossil fuel resources [29]. The 1997 UN General Assembly recognized the need for more sustainable patterns of energy use and took initial steps toward a sustainable energy development program [4]. In 2000, the UN Millennium Declaration was adopted, and the associated Millennium Development Goals were introduced [33]. However, no energy-related targets were contained in this declaration [4]. Energy for sustainable development was a leading topic for the first time at the UN meeting in 2001 [34]. This meeting discussed the importance of energy access to reduce poverty and achieve the Millennium Development Goals, as well as the need to change energy production and consumption patterns [4,35,36]. A follow-up resolution was adopted in 2010, which outlined the energy issues necessary to achieve the Millennium Goals. Particular emphasis was placed on access, efficiency, and sustainable global energy development [37]. In 2011, another initiative was introduced, namely the Sustainable Energy for All [38]. The overarching goal of this initiative is to provide sustainable energy for all by 2030. The main emphasis is placed on energy availability, energy efficiency, and sustainable energy sources. In 2015, the 2030 Agenda for Sustainable Development and its associated Sustainable Development Goals (SDGs) were ratified. The objectives of the Sustainable Energy for All initiatives were aligned with Sustainable Development Goal 7: "Ensure access to affordable, reliable, sustainable, and modern energy for all". With the introduction of SDG7, it was recognized that energy is essential for climate protection (SDG13: Climate Action) and for achieving sustainable development [39]. All these documents testify to the great importance of sustainable energy development of both individual countries and the whole world. Therefore, the idea to study this subject is fully justified and is part of this very current and important problem of the modern world.

Research about Sustainable Energy and Climate Development
The energy and climate sustainability of countries and/or groups of countries constitutes a vast area of scientific research. Studies that look at the concept of sustainable development can be found in the available literature [23,[40][41][42][43][44][45][46][47][48][49][50].
Many of them deal with issues related to sustainable energy and environmental development. The popularity of this topic is due to the fact that environmental protection and energy development concern practically all countries worldwide. The dominant themes of these papers are issues related to sustainable energy and environmental development in the context of climate protection. They mainly focus on the analysis of the operation and assessment of energy systems in terms of their impact on economy, society, and environment.
Research on sustainable energy development and its level has concerned various countries [40][41][42][43][44][45][46][47] or groups of countries [23,[48][49][50]. However, the available literature lacks studies devoted to the assessment of the level of sustainable energy development in the EU-27 over the past 10 years. This is confirmed by the presented review of published works on energy and climate sustainability of individual countries and regions.
Wang et al. in their paper [40] presented research results on the importance of RES in sustainable energy and climate security in China. They used the Divisia index method for their study. Zhao and Guo [41] presented research results on the evaluation of RES in China. They conducted the research using the hybrid Multiple-criteria decision-making (MCDM) method and found that it is necessary to promote photovoltaics to promote this source of sustainable energy.
Erdil and Erbıyık [42] used the SWOT analysis to investigate the sustainable character of solar, biomass, geothermal, wind, or hydro energy in Turkey. On the other hand, Petinrin and Shaaban analyzed the sustainability of renewable energy in Malaysia by discussing different policies for these energy sources [43]. Yu et al. [44] examined the sustainable energy development of 30 provinces in China. They used the ANP method for their study. The evaluation concerned a 5 year time frame. In turn, Fang et al. [45] used the TOPSIS method to evaluate Chinaʹs sustainable energy security. Saraswat and Digalwar [46] evaluated both conventional and renewable energy sources to achieve sustainable energy development in India. The results showed that solar, wind, and hydro energy are best for this development in India. Adenle [47] evaluated solar energy technology in Africa to identify both opportunities and challenges in achieving Agenda 2030 and sustainable development goals.
García-Álvarez et al. in work [23] presented the synthetic energy sustainability index for 15 EU countries. The indicator also includes the environmental aspect related to climate change in the form of the intensity of the emitted CO2 indicator.
Chudy-Laskowska et al. [47] utilized the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method to classify the EU countries in terms of the differentiation of wind energy development levels in the EU. The results indicate that Denmark is the leader in wind energy development in the EU, while Malta is at the other end of the list-the country with the lowest level of sustainable wind energy.
Su et al. [48] compared the sustainability status of the energy sector in 21 EU member states and China. For this purpose, they used the Vlse Kriterijuska Optimizacija I Komoromisno Resenje (VIKOR) method. The results showed that China lags behind the EU countries in terms of energy sector sustainability.
The results of the study showed that Denmark, the Netherlands, France, Portugal, and the United Kingdom performed best in energy sustainability in 2012. On the other hand, Sobczyk and Sobczyk in their study [50] conducted the analysis of the diversity of the energy mix of Poland and the EU-28 in the context of achieving sustainable development of this country.
The results showed that the use of renewable energy in Poland is below the EU average, but the country made progress in increasing RES in the energy mix between 2010 and 2018.

Research Gap
The presented works in Section 2.2 show that the subject matter of this article is current and concerns an important issue. The concept of sustainable economic development must be associated with both energy and climate issues.
The cited works do not present the results of comprehensive studies on the assessment of sustainable energy and climate development in all EU countries in the long term. This particularly concerns the simultaneous inclusion of indicators describing the key areas of this development, which was done in this article. In addition, these publications failed to refer to the important social dimension of sustainable development, which is the energy poverty of citizens of a given country. This aspect may be crucial in gaining social acceptance for the changes related to energy transition.
Moreover, the discussed publications failed to discuss the changes in the studied areas over a period of, for example, 10 years, to indicate the leaders of these changes, or to designate groups of countries with similar indicators. The quantitative and comprehensive studies of the sustainable energy and climate development of the EU countries in this field provide an opportunity for objective assessment and the use of the results to create effective and socially acceptable climate and energy policy.
Therefore, it can be concluded that this paper fills the research gap in the field of sustainable energy and climate development of the EU-27 and provides new and valuable knowledge in this area.
The diversity of the EU countries and, despite a common policy, a certain independence in the creation of internal policy-also in the field of environmental protectionmakes it necessary to conduct a broad and, as far as possible, objective assessment of their energy and climate development.
In the context of the presented literature review, the research approach proposed in this paper is novel, and the obtained results should enrich the knowledge of the assessment of the state of energy and climate sustainability in the EU countries. The adoption of as many as 14 indicators for the analysis makes this approach comprehensive and gives great opportunities for the objective assessment of changes reported in this area. In order to rank and evaluate the level of energy and climate sustainability, the entropy-COPRAS hybrid method was used, which, according to the authors, is adequate for the analysis of this complex and multicriteria research problem.

Data
The analysis presented in the article was carried out on the basis of indicators monitoring the implementation of the Sustainable Development Goals, published by the European Statistical Office Eurostat for the years 2009-2018. In general, these indicators allow for monitoring the progress in achieving the sustainable economy of the EU countries. The analysis was conducted for 27 countries that are currently members of the EU (excluding the United Kingdom).
Each country was characterized by 14 indicators, which are also the determinants of energy and climate sustainability. These indicators are both stimulants (the higher their value, the better) and destimulants (the lower their value, the better). These variables are discussed and presented in Table 1. Source documents related to the indicators are also presented in Table 1.
The set of indicators also includes the economic factor, namely GDP per capita, which is the measure of wealth in societies and, as shown by research, has a significant impact on sustainable energy and climate development, e.g., [34,47,48,51,52].
As already mentioned, the assessment of sustainable energy and climate development of the EU countries was conducted in four dimensions (areas): energy, climate (environmental), social, and economic. It was assumed that these dimensions are key to the evaluation of this development and prove its coherence. Destimulant -

The Entropy-COPRAS Decision-Making Method
The entropy-COPRAS method was used to assess the energy and climate sustainability of the EU countries. It is the combination of two methods: the method of indicator weighting (entropy) and the COPRAS method, belonging to the group of multicriteria decision-making methods.
The complex proportional assessment (COPRAS) method was developed by Zavadskas, Kaklauskas, and Sarka in 1994 [62]. It is used to evaluate the values of maximizing (stimulants) and minimizing (destimulants) indicators; the influence of which on the results is examined separately. In turn, the entropy method makes it possible to objectively determine the values of the weights for the indicators included in the research [63,64].
The algorithm for this method involves the following steps: 1. To construct the decision matrix for n alternatives and d evaluation criteria: (1) 2. To construct the normalized decision matrix: * ∑ 3. To determine weights by the entropy weighting method for each indicator, according to relations (3) and (4): where: 4. To construct the weighted decision matrix: * * • 5. To determine the maximizing or minimizing index of each criterion given its negative or positive mode: where g indicates the number of positive attributes, n−g represents the number of negative attributes, and Si describes the maximizing and minimizing indices of i-th attribute, according to its type.
1. To calculate the relative importance value (Qi) of each alternative: 2. To select the best alternative: 3. To determine the performance index for each alternative (the performance index is 1 for the best alternative): The COPRAS method makes it possible to make the ranking from the best to the worst alternative (solution). In this case, the alternatives are individual EU countries assessed by the performance indices.
In order to assess the level of the EU sustainable energy and climate development, the Pi efficiency index was used. On this basis, four levels of this development were delineated.
These levels were determined on the basis of the average value of the Pi index and its standard deviation. The obtained values allow for the division of the EU countries into four classes. Obviously, this division is dependent on the level of energy and climate development of a given country.
The division into classes takes into account the following values of the Pi index: 1. Class 1: High level of energy and climate sustainability (safe level): (12) 2. Class 2: Medium-high level of energy and climate sustainability (medium level): 3. Class 3: Medium-low level of energy and climate sustainability (warning level): 4. Class 4: Low level of energy and climate sustainability (dangerous level): (15) where is the mean and is the standard deviation. By obtaining the homogeneous and disjoint groups of objects most similar to each other, the separation and substantive analysis of their essential characteristics is much easier. Objects (countries) belonging to a given typological group are ordered according to the value of the synthetic measure-the Pi index. Figure 1 shows the general scheme of the entropy-COPRAS method. All calculations were performed using MATLAB 9.4 software.

Preliminary Analysis
In order to determine the changes reported in the values of the indicators of the EU sustainable energy and climate development between 2009 and 2018, a comparative analysis was performed. The results are presented in the form of a cumulative diagram in Figure 2. It was assumed that 2009 was the base year for which the percentage changes of the indicators adopted for the study were calculated.
Notes: I1-primary energy consumption per capita; I2-final energy consumption per capita, I3-final energy consumption in households per capita, I4-energy productivity, I5-share of renewable energy in gross final energy consumption; I6-energy import dependency by products; I7-population unable to keep home adequately warm by poverty status; I8-GDP per capita, I9-GHG intensity of energy; I10-Total GHG-GDP intensity; I11-GHG per capita; I12-electricity prices by type of user-medium size house; I13-electricity prices by type of user-medium size consumers; and I14-average CO2 emissions per km from new passenger cars. When analyzing the percentage changes in the studied indicators of sustainable energy and climate development in individual EU countries (Figure 2), significant differences in this process can be noted.
In the case of the reduction of primary energy consumption per capita, the best progress was achieved by Greece, which decreased this consumption by almost 21% in the studied period. The opposite result was obtained by Estonia, where the primary energy consumption per capita increased by about 32%. In addition, in the case of final energy consumption per capita, among the EU-27 countries, the highest reduction was achieved by Greece, with a decrease of about 20%, while Lithuaniaʹs final energy consumption was found to have increased by almost 35%. With regard to the indicator for the final energy consumption of households per capita, the highest reduction was achieved by Luxemburg (−20.46%), while in Malta, it increased by 23.72%. In the case of the share of renewable energy in gross final energy consumption, Malta showed the best result between 2009-2018-an increase of more than 3000% (from 0.021% to 7.968%), while in Slovenia the increase was only 1.21% and was the smallest in the entire EU-27. As far as energy import dependency is concerned, the greatest improvement was reported for the Netherlands (by more than 70%). In terms of the energy poverty indicator, the best result was achieved by Poland (reduction of poverty in 2018 versus 2009 by almost 70%), and the worst by Luxembourg, where the indicator increased by 600% (from 0.3% to 2.1%). With regard to the GHG emissions per capita, Malta was found to have a reduction of more than 28%, while Estonia increased its GHG emissions in 2018 versus 2009 by more than 20%.
Malta also saw the largest reduction in the GHG emission intensity of over 35%, while Latvia saw an increase of nearly 10%.
In terms of energy prices for medium-sized houses, the best result was achieved by Malta, where the price fell by over 24%, while in Spain energy prices increased by over 50%. In the case of GDP per capita, the highest increase was reported in Lithuania at more than 90%, and a negative result was noted in Greece, where the value of GDP per capita decreased by more than 20% when compared to 2009, which is mainly due to the economic crisis in the country [65].   (Table 2).  It was found that the clear leader of the ranking throughout the studied period was Sweden, and the country that was last in the ranking was Bulgaria. Between 2009-2018, Spain (from the 13th place in 2009 to the 6th place in 2018) and Lithuania (from the 24th to the 17th) achieved the biggest rise in the ranking. Malta, on the other hand, saw the biggest decline, from the 9th place in 2009 to the 22nd in 2018, and Luxembourg from the 18th to the 25th place.

The Common Assessment of the EU-27 Countries in Terms of Their Energy as well as Energy and Climate Sustainable
In general, the EU countries were reported to improve the values of energy and climate sustainability indicators between 2009 and 2018, yet each country showed its own dynamics of change in this regard.
In the next stage, the determined values of the Pi index made it possible to divide the EU countries into four classes. Each EU country in successive years, from 2009 to 2018, was classified into one of the four classes of sustainable energy and environmental development in terms of the level of this development. In order to assess this level, a 4-point scale was used, with the arithmetic mean and standard deviation calculated from the values of the Pi index (Equations (10)-(13)) ( Table 3). Table 3 and Figure 4 show the groups of similar countries in terms of the level of energy and climate sustainable development.  When analyzing the results (Table 3 and Figure 4), the highest level of energy and climate sustainable development was found for three countries: Sweden, Denmark Based on the analysis of the whole period, it was found that the high level of energy and climate sustainable development was reported for three countries: Sweden, Denmark, and France and Austria, and the low level (dangerous) for Poland, Cyprus, and Bulgaria. The remaining countries were characterized by the high medium level and low medium (warning) levels. In the case of Sweden, Denmark, and Austria, this result is completely understandable, because, as the authors [66][67][68][69][70][71] indicate, these countries already embarked on the path of energy transition toward green energy and climate protection in the 1970s and 1980s.

Assessing the EU Sustainability in the Energy, Climate (Environmental), Economic, and Social Dimensions.
According to the model presented in Section 2, which enables the ranking and assessment of the EU countries in terms of the level of energy and climate sustainable development, an analysis of this development was made for each studied dimension, i.e., energy, climate, economic, and social.
Based on the results of the ranking of the EU countries only for the climate (environmental) dimension, in the period between 2009-2018, Sweden and France were characterized by the high level of GHG emissions. In 2010, this level was also reached by Austria and Portugal, while in recent years (2013, 2016-2018), Malta was also found to show the high level of these emissions. Sweden, which is the clear leader of the ranking (Figure 6), was found to have the lowest GHG emissions from the energy sector and the total GHG-GDP intensity, as well as some of the lowest total GHG emissions per capita. In addition, the average CO2 emissions per km from new passenger cars were found to be among the lowest of all EU countries. Among the industrialized countries, Sweden was reported to have relatively low GHG emissions not only within the EU group but also worldwide. It is crucial to note that Sweden has a lot of trees planted, which further reduces carbon dioxide. Therefore, the emissions balance is close to zero [72]. It is also important to note that Sweden is predicted to become fully climate neutral by 2045.
The worst situation regarding sustainable development only in the climate dimension was found to be in Bulgaria, Poland, the Czech Republic, and Estonia. As far as Estonia is concerned, it belongs to the countries where GHG emissions per capita have been the highest in the EU for many years. In addition, the average CO2 emissions per km from new passenger cars are among the highest in the EU. A similar situation was reported in Bulgaria, where the total GHG-GDP intensity is the least favorable among all the EU countries.
With regard to the economic dimension of energy and climate sustainable development, the best results in the whole analyzed period were achieved by Luxembourg, a country which not only has the highest GDP per capita among the EU countries but also one of the highest in the world [73]. This result was also influenced by the very favorable value of the energy productivity indicator, which is one of the highest in the EU. The high level of development in the economic dimension was also observed in Sweden ( The last immensely important, studied aspect was the social dimension, which concerned the issue of energy poverty of the EU countriesʹ inhabitants. The high level of sustainable development was found in Luxembourg, Sweden, Finland, the Netherlands (2009)(2010)(2011)(2016)(2017)(2018), and Denmark (2009,2016). An exceptionally unfavorable situation in this dimension was reported in many EU countries, for example, in Bulgaria, Romania, Cyprus, Greece, Lithuania, Portugal, and Malta.
The inclusion of this indicator in the assessment of energy and climate sustainable development seems fully justified, although it has not been considered so far. However, according to the assumptions of the concept of sustainable development, this indicator is extremely important. Energy poverty is a situation in which a household or a person does not have the possibility of financing basic energy services (lighting, heating, cooling, mobility, and electricity), ensuring a decent standard of living. This is the consequence of low income, high energy costs, and poor energy efficiency of buildings, the heating of which is also a major environmental hazard [74]. In the EU as a whole, there are approximately 50 million families living in energy poverty, which is unbelievable. This is an immensely unfavorable situation that affects a large part of the EU population. Therefore, the social dimension seems fully justified to be included in the presented analysis.

Assessing Individual EU27 Countries in Terms of Their Energy and Climate Sustainability between 2009-2018
This section presents the analysis of the trends of changes in energy and climate sustainability in individual EU countries for each study year. The purpose of this analysis was to show the trends of changes reported in these countries during the 10-year period. Figure 7 presents the values of the Pi index of energy and climate sustainability in each EU-27 country in the studied years. The results show a large variation in the trends of changes across countries. In many countries, there has been an upward trend since 2009, which is undoubtedly related to the EU energy and climate policy. The framework of this policy was adopted by the European Council in 2007, and the 2020 strategy, which is to stimulate sustainable economic development of the EU countries, was adopted by the European Commission only in 2010. It was in this strategy that the targets to be achieved by 2020 were set: namely, a reduction of at least 20% in GHG emissions compared to 1990 levels; an increase to 20% of renewable energy in all sources of energy consumed; and a 20% improvement in energy efficiency [75,76].
The results also show that in most EU countries, the largest increases were reported between 2011 and 2012, which may be the result of the implementation and execution of this strategy. In general, it can be seen that in many countries, 2018 was the best year for energy and climate sustainability. This is because the EU attaches particular importance to energy transition and protecting the environment from climate change. The results show that all EU countries are implementing the goals of the Europe 2020 strategy and the 2030 Agenda, albeit to varying degrees.
It can be concluded that very significant progress in sustainable development in the studied years was achieved by the Czech Republic, Germany, Estonia, Ireland, Lithuania, Hungary, Luxembourg, Malta, Poland, Slovakia, Romania, and Italy. These are countries, which have clearly reduced GHG emissions (both in total and from the energy sector), increased the share of RES in the energy mix [77], improved energy productivity, and reduced the level of energy poverty.
Among all the EU countries, Denmark clearly stands out. It is the only country where energy and climate sustainability does not show an upward trend. The main reason for this is the fact that in Denmark, between 2009-2012, the index of energy dependence on imports was characterized by a negative value, and since 2013, the energy dependence of the country on energy imports has been steadily increasing, which negatively affects the value of the Pi index of energy and climate sustainability.

Discussion
For many years, energy and climate policy has been the priority area of activity for the EU, and in recent years, it has become increasingly important [77,78]. Currently undertaken activities are closely related to the European Green Deal and are part of the implementation of the objectives of Agenda 2030 (goals: 7 on "Clean and Accessible Energy" and 13 on "Climate Action"), adopted in 2015 by the UN General Assembly. It resulted in very ambitious sustainability assumptions that focus on the transformation of the energy sector and the achievement of climate neutrality.
The main objectives of introducing sustainable economic development is to ensure the economic development of the EU and improve the state of the environment and the welfare of societies [79]. In these processes, energy policy, which is closely related to climate protection activities, is of great importance. It has resulted in a number of legislative acts, including the white paper with respect to renewable energy (1997), aimed at encouraging the implementation of sustainable energy and climate development [80]. They are designed to promote a market for renewable energy, encourage energy efficiency, and reduce GHG emissions into the atmosphere. A landmark year for this process was 2009, when the first groundbreaking legislation on climate change was adopted (Europe 2020 strategy). Therefore, the study presented in this paper includes data from that year onwards.
The aim of this study was to assess the level of the sustainable energy and climate development of the EU countries over a 10-year period based on 14 selected indicators characterizing the four main areas (dimensions) of the economic life of the EU countries (energy, environment, economy, and society). The adopted set of indicators made it possible to assess the sustainable energy and climate development of the EU countries in a very broad range, considering many factors characterizing the diversity of the countries in question. Moreover, the values of the indicators like final energy consumption, primary energy consumption, final energy consumption in households, GHG emissions, and GDP were compared to the population of a given country, which additionally allowed us to consider the demographic factor. The classification and division of the EU countries was based on the value of the Pi index of sustainable energy and climate development determined on the basis of the adopted indicators by means of the entropy-COPRAS method.
The study showed significant changes in the values of the indicators adopted for the research in the examined period, which also translates into the results of the evaluation of the level of the EU sustainable energy and climate development. Particular variability was observed in the indicators of energy productivity, the share of renewable energy in gross final energy consumption, GHG emissions per capita, average CO2 emissions per km from new passenger cars, or population unable to keep home adequately warm by poverty status.
The findings showed that among all the EU countries, in the studied period, the high level of sustainable energy and climate development was reported for Sweden and France. Apart from 2010, Denmark can also be included in this group.
The low level of this development was reported for Bulgaria and Cyprus. The averaging of the assessment results confirmed the low level of this development in these countries during the whole studied period. Moreover, it also showed that the problem of the low level of sustainable energy and climate development also concerns Poland. The low level of sustainable development between 2014-2017 was also found in Greece, between 2011-2014 in Malta, between 2009-2011 and in 2018 in Poland, and for single years also in the Czech Republic, Estonia, Lithuania, and Luxembourg (the country with the highest values of GDP per capita [81]). The economic and social indicators were found to be really low in these countries, which results in the high exposure of their inhabitants to energy exclusion caused by the low quality of energy supplied, its availability, and high price [82,83]. These results show some differences versus the results presented in another work [15], in which the leaders in energy sustainability for 2017 included Denmark, Luxembourg, Austria, and Sweden, respectively, with Cyprus and Bulgaria ranking last. Luxembourgʹs high position in this study was due to its wealth rather than energy or climate factors. The differences in terms of assessment were influenced by the different set of indicators adopted for the study and the fact that the authors did not take into account the weights for individual indicators of sustainable energy development.
Another study [66] also presents the results of the research on the ranking of the EU countries in terms of energy development. They were shown to differ from those obtained in this article. However, the analysis in this paper was conducted only for 18 countries, and the best results were achieved by Denmark and France.
Completely different results are presented in another paper [28], which evaluated sustainable energy development in the context of the share of RES in the energy mix. In this study, Germany was the leader of the ranking made for data from 2007-2016.
The results also made it possible to identify countries and the leaders of the ranking, in terms of the level of sustainable energy and climate development in individual dimensions (energy, climate, economic, and social) ( Table 4). The results of this part of the study showed that the richest country in the EU in terms of GDP per capita was Luxembourg [60]. It was found to have reached a high development level in the economic and social dimensions, but for all indicators related to energy and climate dimensions, it was found to show only an average low level. The reasons include the highest energy consumption per capita in the EU (primary energy consumption, final energy consumption, and final energy consumption in households per capita), the low share of renewable energy in the energy mix, high dependence on energy imports, the highest GHG emissions per capita in the EU, and high energy prices.
When analyzing the results of the assessment of the level of sustainability of each country over the studied 10 years, it can be concluded that most of them showed an increasing trend. The only exception is Denmark, which is related to the deterioration of its energy independence [21]. In general, however, in most countries the values of the studied indicators were found to have improved. In some countries, such as Poland, Finland, and Sweden, it was noted that the best evaluated year was 2015. Unfortunately, after this year, in these countries, a temporary increase was reported Sweden was found to be the clear leader in sustainable energy and climate development among the EU-27 countries during the studied period (Table 2), as well as in terms of the climate dimension. This is due to the energy transition that started in the 1970s. Moreover, Sweden has a long tradition of developing an ambitious environmental policy [67][68][69]83,84]. In this case, several issues are worth noting. Only two countries (Luxembourg and Finland) consume more primary energy per capita than Sweden, and yet the carbon dioxide emissions per capita are relatively low when compared to other EU-27 countries. The average carbon dioxide emissions between 2009-2018 were reported to be 6.0 tons per capita (only Latvia showed lower emissions-5.9), while in the richest country like Luxembourg, these emissions were found to be 23 tons per capita (almost four times higher). At the same time, the low emissions of harmful substances are accompanied by the economic growth of the country. Between 2009 and 2018, Sweden ranked fourth among all EU countries in terms of average GDP per capita. This result also has an impact on the problem of energy poverty, which is very low in Sweden. On average, just over 1.8% of the population was affected during the studied period, while in Bulgaria, a country with the low level of energy and climate sustainability, the problem affected on average over 44% of the countryʹs population during the period in question.
Another country that showed favorable results is Denmark. This countryʹs high level of energy and climate sustainability is the result of the long process of energy transition that began in the 1970s. The oil crisis, dependence on imports, and environmental pollution were the main determinants of this process consisting in moving away from fossil fuels toward RES, mainly wind energy [69,85]. Denmarkʹs high score was influenced by the fact that between 2009-2012, it was the only net exporter of energy among the EU member states, but in 2013 Danish energy imports exceeded exports, and this trend was confirmed in the following five years until 2018.
By contrast, very poor results were reported for Bulgaria. It is a country with the lowest average value of GDP per capita, among the EU countries in the studied years, which amounted to only 6,165 Euros (it is slightly better in Romania, where the level of sustainable energy and environmental development in the studied period was assessed as medium low). However, this country is gradually developing a renewable energy sector based on domestic energy sources [86]. Their development is visible in the presented results, and it should be assumed that in the coming years, Bulgariaʹs indicators will significantly improve. While in 2009, the country imported about 45% of energy, and in 2018, this indicator dropped to just over 36%, which is the fifth lowest result in the entire EU-27. The increase in electricity production from RES reduced the environmental footprint of the countryʹs energy system in terms of GHG emissions. However, the total environmental footprint in terms of GHG emissions increased from 7.9 to 8.1 tons per capita. Nevertheless, Bulgaria still remains a country where the problem of energy poverty affects a large number of inhabitants (an average value for 2009-2018 amounts to 44%).
A country that is heavily dependent on imported energy (nearly 93% in 2018) is Cyprus. However, the country is gradually increasing the use of RES. As the Cypriot energy system is based on conventional energy sources, the country also has one of the highest GHG emissions from the energy sector and total GHG emissions per capita. In addition, it also has one of the highest average CO2 emissions per km from new passenger cars. By contrast, the energy poverty rate of the countryʹs residents-which affects nearly 22% of citizens-remained unchanged between 2009 and 2018.
When looking at the listed countries in terms of energy and climate sustainability, Luxembourg should be highlighted. This country was found to be the richest in terms of GDP per capita of all EU countries. However, despite the best economic conditions and the lowest degree of energy poverty (high level of development of the country in economic and social dimensions- Figure 6, Table 4), it is a country with an average low level of energy and climate sustainability. This is influenced by several factors. Luxembourgʹs energy system is characterized by high import and fossil fuel dependence. The countryʹs renewable energy share between 2009-2018 was one of the lowest in the EU countries, with only 2.9% in 2009 and 9.1% in 2018 (only Malta and the Netherlands had a lower share in 2018). Therefore, Luxembourg has implemented a renewable energy transfer policy to achieve the EU RES targets. These transfers (from Estonia and Lithuania) will be used to close the gap to the 2020 target of 11% renewable energy in gross final energy consumption. Luxembourgʹs energy-efficiency improvements were reported to be positive until 2016 but have recently been increasing again. Poland, Portugal, Hungary, the Czech Republic, and Denmark are also facing similar problems. However, Luxembourg has a policy aimed at introducing stricter targets and a more robust approach to energy transition in the EU [87].
In general, the countries studied comply with the EUʹs commitments contained in the climate and energy package, for example, increasing the share of renewable energy and improving energy efficiency, mainly in order to reduce greenhouse gas emissions. However, the level of effectiveness in this area varies in individual countries.
Nevertheless, as the authors of one paper [88] indicate, the EU countries should make much more effort to reduce energy consumption and increase the share of RES to achieve the goal of reducing greenhouse gas emissions, which is set out in the Paris Agreement.
Due to the comprehensiveness of the paper, the discussion of the results concerned only the most important issues, according to the authors. The findings enable a much broader discussion. This is because it is possible to refer to the analysis of the variability of individual indicators for the studied countries, the analysis of trends in their changes, the analysis of similarity, and many other aspects. The possibilities of studying these results and making conclusions based on them are very large. The choice in this area is left to the readers of the article, especially since the available literature lacks the approach presented in this paper for the analysis of the state of sustainable energy and climate development for any group of countries.

Conclusions, Policy Implications, and Direction of Future Research
The results presented in the paper add value to the current state of knowledge and may contribute to other possibilities of monitoring progress in the implementation of the EU Sustainable Development Strategy for modern energy and climate activities.
The issues related to the implementation of the principles of sustainable economic development is currently one of the most interesting research topics. The legitimacy of undertaking this subject stems from the need for changes in the global economy to protect the environment and provide development opportunities for future generations. These goals are becoming increasingly dominant in individual regions of the world. The unquestionable leader in the process of transforming the economy in accordance with the idea of sustainable development is the European Union. Of key importance for the effectiveness of this process are changes in the energy sector, which significantly influenced the current climate problems. Therefore, the EU is undertaking, to a significant extent, actions aimed at improving the state of the environment, through the implementation of ambitious goals related to the sustainable development idea, included in the concept of the European Green Deal and Agenda 2030.
As a result of these activities, the EU is currently the absolute leader in implementing concepts and ideas related to both climate protection and sustainable development.
The findings presented in this paper fit well into this area of the EU activity. The Pi index, adopted in the study, enabled an objective assessment of the EU countries for the period 2009-2018 in terms of sustainable energy and climate development. It can be assumed that the value of this index, determined on the basis of 14 indicators representing energy, climate, social, and economic dimensions, is an objective measure of sustainable energy and climate development. Therefore, this analysis considered the priority areas of the EU's activities in terms of the latest concept of the European Green Deal and goals 7 and 13 of the 2030 Agenda for Sustainable Development.
The results show that throughout the studied assessment period, significant changes were observed in the values of input indicators, which directly affected the value of their weights and thus the value of the Pi index-which was the basis for the assessment of this level. They also show the trends and effects of actions undertaken by the countries in the examined areas and years.
In addition, both leaders in transformation and countries that still have a lot to do in the field of energy transition and climate protection were reported.
The created ranking of the EU countries and their division into four groups clearly identifies countries that require more intensive assistance, both in terms of content and finance. It is obvious that changes related to sustainable economy require investments and not all EU countries are able to finance them. Among the countries that require special attention in this regard are Bulgaria, Cyprus, Poland, Estonia, Greece, Lithuania, Malta, the Czech Republic, and Luxembourg. Climate protection is a global problem, and its implementation requires solidarity from the more affluent countries for the benefit of those with problems. It seems that in the case of the EU, this solidarity and cooperation is generally considered the standard, without which the very ambitious plans contained in the concept of the European Deal Green and the 2030 Agenda cannot be achieved.
It should be emphasized that the transition paths of individual countries to achieve sustainable energy and climate development in the EU differ between member states. Despite the overarching goal of the entire EU, individual countries, depending on their internal situation, implement their own policies. This is due to the great economic diversity of individual countries, their economic potential, geopolitical location, and other factors. It should also be remembered that the EU consists of as many as 27 rather small countries. Therefore, it seems obvious to target financial actions to groups of countries with similar conditions and problems, as well as to use the experience of the leaders in the field of energy transition and climate protection. The presented analysis covers both these elements. On the one hand, it identifies countries with the best results in order to benefit from their experience (e.g., Sweden, Denmark, France, and Austria), and on the other hand, it identifies groups of countries that should cooperate to achieve the assumed objectives (e.g., Poland and Bulgaria). These analyses also point to the possibility of specializing in certain elements of energy policy by individual countries, such as obtaining energy from RES.
In addition, the time requirements for achieving certain goals must be adjusted to the economic possibilities of all member states. Researchers working on this topic point out, for example, that in some countries of Central and Eastern Europe, the energy and climate transition will generate enormous and much higher costs than in more developed countries [89][90][91]. This is the result of a different energy structure and outdated energy systems (e.g., in Poland and Bulgaria). These challenges may cause many adverse effects, such as an increase in energy prices, loss of jobs, and thus slow down economic development, while at the same time hindering social acceptance of the new energy and climate policy.
The conducted research has also confirmed the great diversity of the EU countries, which, on the one hand, is an unquestionable advantage and testifies to its size but on the other hand, may also constitute a serious barrier to the implementation of common policies, such as energy and climate policy.
Energy and climate sustainability is the essential component of sustainable development. It is the process of sustainable, safe, and effective provision of energy and climate protection for present and future generations.
The application of the entropy-COPRAS method for multicriteria analysis, which belongs to the group of multicriteria assessment methods, should be evaluated positively. The results define a new dimension of research on the sustainable energy and climate development of the EU countries. This method is universal and can be successfully used to analyze other groups of countries.
In terms of the sustainable energy and climate development of individual countries and groups of countries from different regions worldwide, it is necessary to conduct further research, especially on the methodology of the construction of indicators that allow the most objective assessment of the changes made.
It should also be borne in mind that these indicators consider factors specific to individual countries. This means that the set of indicators must be adjusted in terms of their meaning and practical usefulness. At the same time, they should be balanced in terms of representing all the necessary dimensions that make up the sustainable energy and climate development of countries, i.e., the energy, climate, economic, and social dimensions.
Therefore, it is advisable to carry out further research in the field of the implementation of energy and climate policies of both countries and their groups in order to continuously evaluate the introduced changes and identify problems in their implementation.