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Article

Advancing Sustainable Development Goal 4 Through Green Education: A Multidimensional Assessment of Turkish Universities

by
Bediha Sahin
Faculty of Education, Hacettepe University, Beytepe, Ankara 06800, Türkiye
Sustainability 2025, 17(19), 8800; https://doi.org/10.3390/su17198800
Submission received: 7 September 2025 / Revised: 29 September 2025 / Accepted: 30 September 2025 / Published: 30 September 2025
(This article belongs to the Special Issue Sustainable Education for All: Latest Enhancements and Prospects)
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Abstract

In this study, we provide, to our knowledge, one of the first multidimensional, data-driven evaluations of green education performance in Turkish higher education, combining the THE Education Score, THE Impact Score, and the UI GreenMetric Education & Research Score (GM-ED) with institutional characteristics, and situating the analysis within SDG 4 (Quality Education). While universities worldwide increasingly integrate sustainability into their missions, systematic evidence from middle-income systems remains scarce. To address this gap, we compile a dataset of 50 Turkish universities combining three global indicators—the Times Higher Education (THE) Education Score, THE Impact Score, and the UI GreenMetric Education & Research Score (GM-ED)—with institutional characteristics such as ownership and student enrollment. We employ descriptive statistics; correlation analysis; robust regression models; composite indices under equal, PCA, and entropy-based weighting; and exploratory k-means clustering. Results show that integration of sustainability into curricula and research is the most consistent predictor of SDG-oriented performance, while institutional size and ownership exert limited influence. In addition, we propose composite indices (GECIs). GECIs confirm stable top performers across methods, but mid-ranked universities are volatile, indicating that governance and strategic orientation matter more than structural capacity. The study contributes to international debates by framing green education as both a measurable indicator and a transformative institutional practice. For Türkiye, our findings highlight the need to move beyond symbolic initiatives toward systemic reforms that link accreditation, funding, and governance with green education outcomes. More broadly, we demonstrate how universities in middle-income contexts can institutionalize sustainability and provide a replicable framework for assessing progress toward SDG 4.

1. Introduction

The Sustainable Development Goals (SDGs), adopted in 2015, set a shared agenda for social well-being, economic prosperity, and environmental protection by 2030 [1]. Within this agenda, SDG 4 (quality education) is pivotal because progress in learning and equitable access amplify many other goals across the system [2]. Higher education institutions (HEIs) are central to this important and transformative task.
Universities advance the SDGs through teaching, research, policy engagement, and their own campus practices, increasingly weaving sustainability into curricula, research portfolios, operations, and strategic planning [3,4]. This integration strengthens SDG 4 while preparing future professionals to address cross-cutting challenges [5,6]. This aligns particularly with SDG Target 4.7, which calls for education systems to integrate sustainability, human rights, and global citizenship into curricula so that learners acquire the knowledge, skills, and values necessary for sustainable development.
In addition to this, it also raises a theoretical question: is sustainability in higher education primarily an operational adjustment or a transformative learning process that reshapes institutional missions [7].
Recent studies indicate uneven and context-dependent progress. While many universities (especially in parts of Europe, North America, and Asia) have institutionalized sustainability, others face fragmented implementation and resource constraints [8]. Global benchmarking frameworks (e.g., THE Impact Rankings, UI GreenMetric) have increased visibility but also attracted critique for potentially oversimplifying complex institutional efforts, underscoring the need for multidimensional, comparative approaches that connect global indicators to local contexts and move beyond descriptive case studies [9,10].
In Türkiye, interest in sustainability within higher education is rising, yet empirical work remains narrow. Many studies either document initiatives or discuss ranking outcomes without systematically linking them to educational structures, governance, or student engagement [11,12]. The need for integrated, data-driven analyses limits the comparative evidence available to policymakers and university leaders, despite a rapidly expanding and diverse sector where global competitiveness is a policy priority [13,14,15]. For this reason, Türkiye offers a valuable setting to examine the determinants of “green education” performance.
Against this situation, we ask: (i) To what extent do global sustainability indicators—THE Education, THE Impact, and UI GreenMetric—converge in assessing universities’ contributions to SDG 4? (ii) Which institutional characteristics (e.g., public vs. private status, enrollment size) systematically explain performance differences? Unlike prior descriptive accounts, we develop a comprehensive dataset that combines global indicators with institutional features and apply statistical analysis alongside composite indexing and clustering to capture multidimensional performance. In doing so, the paper (1) empirically evaluates the consistency and divergence of leading rankings, (2) introduces composite and clustering methods to move from benchmarking to explanation, and (3) situates the Turkish case within broader debates on governance, equity, and global sustainability in higher education.

2. Literature Review

Recent studies examine the ways in which HEIs help turn the SDGs into reality. Leal Filho et al. [3] note that their role goes beyond SDG 4 on quality education, extending to climate action, gender equality, and building sustainable communities. Fonseca et al. [2] add that education is closely connected to nearly all other SDGs and can act as a driver of wider sustainable development. One major area of research focuses on how sustainability is integrated into the curriculum and institutional structures of universities. Ceulemans et al. [16] underline that engaging stakeholders is essential when designing programs with a sustainability focus. Albareda-Tiana et al. [5] observe that universities embedding sustainability within teaching, governance, and campus life are more likely to secure lasting progress toward the SDGs. Nonetheless, how deeply and consistently these practices are applied varies greatly from one country and institution to another. Anand et al. [17] studied a regional initiative in Quebec, Canada. Recent research, such as Estorani Polessa et al. [18] on a Brazilian university and Sribanasarn et al. [19] on a Thai institution, confirms that while sustainability integration is a shared global concern, the specific approaches and results are shaped by local contexts. These cases underline the context-dependent nature of institutional strategies, but they also reveal an important limitation: the literature still lacks comparative, data-driven frameworks that connect curricular reform to measurable outcomes across higher education systems [20]. In addition, the interaction between curriculum design, governance structures, and student engagement remains insufficiently theorized, even though these elements are critical for achieving progress on SDG 4 [21]. As a result, the field continues to rely heavily on isolated case studies, with limited theoretical synthesis across settings. A growing body of scholarship argues for integrative models that bring together education-theory perspectives—such as transformative learning and Education for Sustainable Development—while also ensuring the use of verifiable indicators to support benchmarking across institutions [22].
Green education is gaining recognition as a key pathway for integrating sustainability principles into formal education systems, thereby contributing to the wider realization of the SDGs [23]. Studies such as Varela-Candamio et al. [24] and Venkataraman [25] have highlighted the importance of the green education concept. This concept provides students and educators with resources and learning environments that encourage them to think critically about global environmental problems and their solutions [26]. In addition to this, green education can enhance learning outcomes, which aligns with SDG 4. SDG 4 calls for inclusive and equitable education and for lifelong learning for all [27]. Khalili et al. [28] show that cleaner production improves environmental outcomes through recycling, waste reduction, and resource reuse at the organizational level. They call for integrated strategies that balance ecological and socio-economic goals. The study also highlights capacity building and offers a practical framework to help higher education leaders assess and design training programs aligned with the SDGs. Recent work adds that competencies such as systems thinking, anticipatory governance, and collaboration should be treated as core learning outcomes of green education, as these competencies connect classroom practice to institutional change and societal impact [29]. In other words, green education emerges not only as a pedagogical innovation but also as a strategic approach that ties classroom learning with broader institutional reform. In this sense, green education represents not just a pedagogical adjustment but a whole-institution transformation involving governance, research agendas, and organizational culture [30].
HEIs are now expected to strengthen their physical and organizational capacities while also preparing students with the values and knowledge needed to advance sustainable development. In this context, the incorporation of sustainability principles into university curricula, often referred to as green curricula, has gained particular momentum in the post-2000 era. Metrics such as those used in the UI GreenMetric Rankings highlight sustainability education as a core performance indicator [31]. Reflecting this trend, numerous studies have examined how academic programs integrate environmental and sustainability themes. For example, Xiong et al. [32] assessed the sustainability content in Chinese university curricula, while Wang et al. [33] underlined the significance of the United Nations’ Education for Sustainable Development (EfSD) initiative in advancing curriculum reform. Other researchers, such as Beynaghi et al. [34], have explored potential future pathways and critical barriers to embedding sustainability education. Dagiliūtė et al. [35] further emphasize the role of student engagement in advancing curricular change, drawing on comparative case studies conducted in Lithuania. Nevertheless, evidence frequently points to partial adoption (e.g., elective modules, pilot projects) rather than comprehensive, mandated integration across programs and departments [36]. Institutional fragmentation—such as the separation of teaching, operations, and outreach units—has been shown to weaken coherence, producing symbolic rather than structural change [37]. Thus, while many initiatives exist, the literature suggests a tension between symbolic commitments and structural reforms, indicating the importance of governance mechanisms that can bridge silos. This indicates a need for governance mechanisms that can bridge silos and align diverse initiatives under a unified sustainability strategy.
As green education matures and universities align practice with the SDGs, we need clear, comparable measures of sustainability. Berzosa et al. [38] contend that ranking exercises increase public scrutiny and bolster institutional accountability. In this vein, GreenMetric’s Education & Research (ED) component is often used to gauge how far sustainability has been mainstreamed into academic work. Yet, as Burman et al. [39] warn, single-number indicators can flatten nuanced practices and miss qualitative features such as curriculum content or interdisciplinarity. A further issue concerns what the metrics truly measure: divergent indicator architectures, weighting rules, and data-collection routines across rankings can favour well-resourced universities and obscure genuine pedagogical shifts elsewhere [40]. The result is a methodological tension—greater transparency, but weaker like-for-like comparability. Hence the core question raised by Stough et al. [41]: do these metrics evidence institutional transformation, or mainly reflect reporting muscle and optics? To mitigate these limits, recent work advocates triangulation—combining THE Education, THE Impact, and GreenMetric sub-scores with institutional attributes to obtain a more balanced view of green education performance [42,43].
In Türkiye, research that integrates GreenMetric data with national datasets remains scarce. Although some studies have examined sustainability initiatives at Turkish universities [11,12], few have explored how these efforts correspond to the SDGs in terms of educational structures, strategic planning, or academic output. Recent work has also explored sustainability ranking approaches in the Turkish context (e.g., [44]), but these contributions remain largely descriptive and limited in scope. Our study extends this literature by employing a multidimensional, data-driven design that integrates multiple international indicators (THE Education, THE Impact, GM-ED) with institutional characteristics. Compared to the global literature, where comparative analyses and theoretical debates are expanding, Turkish studies remain predominantly descriptive. In addition, there is a clear absence of comprehensive decision support systems that connect international rankings with localized educational indicators. Most studies still hinge on descriptive cases or single-ranking snapshots, which constrains comparability and blunts policy inference [6]. Türkiye, moreover, remains under-theorized: despite two decades of rapid expansion and diversification, we know little about how institutional form, scale, and governance arrangements condition sustainability outcomes [45]. This makes it necessary to place Türkiye within wider debates on governance and equity in sustainable higher education. What is missing is a design that marries widely used indicators—THE Education, THE Impact, and GreenMetric—with basic institutional attributes (public/private status, enrolment size) to yield calibrated benchmarks and meaningful types [21]. This study takes that step by implementing a composite-index plus clustering strategy tailored to Türkiye, enabling systematic like-for-like comparisons and generating a decision-oriented evidence base for advancing SDG 4.

3. Materials and Methods

This section presents the data and analytical methods used in the study, structured into two parts: data collection and analytical procedures. This framing provides a clear link between the study’s objectives and the empirical strategy.

3.1. Data Collection

The dataset used in this study combines internationally recognized indicators of sustainability and higher education performance for Turkish universities. We collected the data from the Times Higher Education (THE) World University Rankings (specifically, the “Teaching” or education quality score, referred to here as THE Education Score), the THE Impact Rankings (focusing on universities’ performance on the SDGs, including the overall score which encompasses SDG 4), the UI GreenMetric World University Rankings (with a focus on the Education & Research category), and official national higher education statistics for the 2023–2024 academic year. Bringing these sources together ensures that the analysis rests on transparent, comparable, and widely accepted measures. In contrast to earlier studies that relied on a single dataset or descriptive comparisons, this integrated approach allows for systematic benchmarking and explanatory analysis.
The THE Education Score (from THE World University Rankings) captures aspects of teaching quality and the academic environment, including factors such as staff-to-student ratios, doctorate awards, teaching reputation survey results, and institutional resources. Alongside this, the THE Impact Score provides a measure of a university’s sustainability engagement through the lens of the UN SDGs (with SDG 4: Quality Education being a key component for our purposes). Because some institutions report THE Impact results in bands or ranges, midpoint values were calculated for those cases to achieve comparability across institutions. UI GreenMetric indicators were also incorporated, with particular focus on the Education & Research dimension (denoted here as GM-ED Score), which assesses the integration of sustainability into curriculum design, research output related to sustainability, and student involvement in environmental initiatives. For context, each university’s global and national rank in the 2024 GreenMetric was recorded as well. This triangulation of sources provides both breadth (global comparability) and depth (local institutional detail) (see Table 1).
Most available work still describes rather than compares. Case studies and one-off looks at a single ranking make it hard to put institutions on a common footing and leave little to guide policy [6]. In Türkiye the theoretical picture is even thinner. The sector has grown and diversified over the past two decades, yet we still lack clear evidence on how institutional type, size and governance shape sustainability outcomes [45]. This makes it important to read the Turkish case alongside wider debates on governance and equity in sustainable higher education. What is missing, in particular, is an integrated and data driven design that connects recognised metrics such as THE Education, THE Impact and GreenMetric to basic institutional attributes, including public or private status and student numbers, so that robust benchmarks and workable typologies can be built [21]. The present study takes that step by using a composite index and clustering tailored to Türkiye to enable systematic comparisons across universities and to provide a transparent, decision oriented evidence base for advancing SDG 4.
All variables were consolidated into a single dataset, with any reported ranges converted into midpoint averages and numeric scales standardized where necessary. This process resulted in a unified dataset covering 50 universities. Türkiye currently has more than 200 universities overall, but only these 50 institutions reported complete data across all three indicators (THE Education, THE Impact, and GreenMetric). Therefore, the sample was restricted to these universities to ensure comparability and methodological rigor. Compared with prior studies for universities in Türkiye that relied mainly on descriptive comparisons, this dataset is unique in that it systematically integrates three global ranking systems with institutional-level attributes, enabling explanatory analysis rather than simple benchmarking. The selection of these indicators was motivated by three considerations: (1) their international recognition, which allows benchmarking against global standards; (2) their multidimensional character, capturing both educational quality and sustainability engagement; and (3) their alignment with the objectives of SDG 4, which emphasizes inclusive and equitable quality education. Together, these factors provide a robust empirical basis for assessing the state of “green education” in Turkish higher education.

3.2. Analytical Methods

Following data collection and preparation, we conducted several quantitative analyses. At first, we computed descriptive statistics for all key variables to characterize the distribution of educational and sustainability performance across the sample. We performed Welch’s t-tests (allowing for unequal variances) comparing public vs. private universities on the main performance metrics to examine differences between institutional types. In addition to this, Pearson correlation analysis was used to assess the bivariate relationships among the indicators (THE Education Score, THE Impact Score, GM-ED Score, and student enrollment), shedding light on the degree to which these measures coincide or diverge.
Furthermore, to provide an integrated view of performance, we constructed a composite index. Each of the three performance indicators (THE Education, THE Impact, and GM-ED) was normalized to a common scale [0, 1] using min–max normalization. We calculated the Green Education Composite Index (GECI) for each university by taking the simple average of three normalized scores, giving equal weight to teaching quality, sustainability impact, and sustainability education. The idea behind the index is to capture overall “green education” performance—in other words, how well a university balances quality education with sustainability. To check the stability of our results, we also tested other weighting methods, including PCA-based and Shannon entropy weights [46]. This allowed us to see whether rankings shift depending on the method used. Looking at multiple strategies reduces bias in how the index is built and makes the approach more transparent.
Finally, we explored patterns of similarity among universities using a clustering approach. A k-means cluster analysis was applied to the set of normalized indicators (THE Education, THE Impact, GM-ED) to identify groups of institutions with similar profiles. The number of clusters was selected based on interpretability and standard criteria (examining within-group variance reductions). To enhance validity, we further assessed clustering stability using silhouette scores and multiple random initializations, reducing the risk of arbitrary grouping [47,48]. This clustering provides an additional, exploratory perspective on whether distinct types or “archetypes” of universities emerge in terms of their education and sustainability performance.
All analyses were conducted using Python 3.11 and standard statistical libraries. We also employed heteroskedasticity-consistent (HC3) robust standard errors in regression models to account for potential variance heterogeneity across universities, thereby strengthening the reliability of inference [49].

4. Empirical Results

This section presents the empirical results of the study, beginning with descriptive statistics of the dataset and followed by regression, composite index, and clustering analyses to evaluate universities’ performance in green education.

4.1. Descriptives

We show the descriptive statistics on Table 2 for the main indicators across the 50 Turkish universities in the sample. The mean THE Education Score is 20.37, with scores ranging from 11.1 (Bartın University) to 44.2 (Middle East Technical University). The average THE Impact Score is 59.06, with considerable variation between a minimum of 25.9 (Akdeniz University) and a maximum of 93.2 (Istanbul Technical University). The GreenMetric Education (GM-ED) Score averages 1374, with values spanning from 400 (Çankırı Karatekin University) to 1800 (Izmir Institute of Technology). Student enrollment also shows wide dispersion: while small private universities enroll fewer than 4000 students (e.g., Bezmialem Vakıf University), large public universities exceed 70,000 (e.g., Bursa Uludağ University). These initial figures highlight both institutional diversity and the broad range of sustainability performance captured in the dataset.
These descriptive results suggest two patterns: (i) sustainability-related scores (THE Impact and GM-ED) tend to be stronger and more variable than teaching quality scores, and (ii) institutional scale differs dramatically across the system, yet size alone does not appear to predict sustainability performance. This indicates that sustainability engagement may be shaped by factors beyond simple institutional size or capacity.
Table 3 reports the pairwise correlations among the main indicators. THE Education and THE Impact are positively correlated (r = 0.44), suggesting that universities with stronger teaching profiles also tend to score higher in sustainability rankings. GM-ED is strongly correlated with THE Impact (r = 0.54) but only weakly with THE Education (r = 0.17), which implies that sustainability education efforts and global impact measures are aligned, but not necessarily tied to conventional teaching metrics. In other words, sustainability visibility and curricular integration move together, but they only partially overlap with traditional measures of teaching quality.
Table 4 compares mean scores across public and private universities. On average, private universities report slightly higher THE Impact scores (63.1) compared to public universities (58.3), despite enrolling fewer students (≈16,600 vs. ≈39,600). Public universities, by contrast, have marginally higher GM-ED scores (1384 vs. 1321), reflecting their greater infrastructural capacity for sustainability initiatives. These differences, however, remain modest and suggest more within-group than between-group variability.

4.2. Composite Index Results

The three indicators used in this study—THE Education, THE Impact, and GM-ED—capture related but distinct aspects of universities’ educational quality and sustainability engagement. To synthesize these dimensions into a single benchmark, we developed a Green Education Composite Index (GECI) and implemented three alternative weighting strategies: equal weighting, principal component analysis (PCA), and entropy-based weights. This approach allows us to assess both the robustness and sensitivity of institutional rankings. By comparing these approaches, we can distinguish stable leaders from institutions whose positions depend heavily on methodological choices.
Equal-weight Index:
As a baseline, each indicator was normalized to the range [0, 1] using min–max transformation, and an equal weight (1/3) was assigned. This specification assumes that teaching quality, sustainability impact, and sustainability education contribute equally to institutional performance. This method provides a neutral benchmark against which the more data-driven PCA and entropy approaches can be compared.
A Welch’s t-test shows that the gap between public and private universities is not statistically meaningful (p > 0.05). As Figure 1 makes clear, their THE Impact score distributions overlap quite a lot. In practice, this means that whether a university is public or private does not by itself explain sustainability performance. The bigger differences are actually within each group rather than between them. This supports the idea that what really matters is how sustainability is built into strategies and governance, not the formal status of the institution.
PCA-based Index:
The PCA weighting scheme extracts the latent structure of the indicators. The first principal component (PC1) explains approximately 62% of the total variance, with the highest loadings on THE Impact and GM-ED, suggesting that these sustainability-related measures are the primary drivers of cross-university differentiation. Rankings under this method are strongly correlated with the equal-weight results (Spearman’s ρ ≈ 0.91), although mid-tier universities with disproportionately strong GM-ED scores (e.g., Ege University, Hacettepe University) gain relative advantage compared to the equal-weight approach. This indicates that PCA accentuates sustainability-oriented strengths while slightly de-emphasizing teaching quality (see Figure 2).
Entropy-weighted Index:
Entropy weighting accounts for the degree of variability among indicators, assigning higher weights to those with greater informational content. The resulting weights were 0.41 for THE Impact, 0.36 for GM-ED, and 0.23 for THE Education. This reflects the fact that sustainability measures differentiate universities more sharply than conventional teaching metrics. Under this method, universities with strong sustainability profiles (notably Istanbul Technical University and Izmir Institute of Technology) consolidate their standing, while institutions with relatively balanced but moderate scores decline slightly in the rankings. In this sense, entropy weighting rewards specialization in sustainability rather than balanced but modest performance.
Robustness of Rankings:
Despite methodological differences, the overall pattern of results is stable. The identity of top and bottom performers remains unchanged across weighting schemes, with rank shifts largely confined to mid-range universities. The robustness of GECI indicates that composite indices can provide a reliable proxy for evaluating “green education” performance, while also highlighting the sensitivity of middle-tier institutions to methodological specification. Thus, while weighting choices matter for relative positioning, they do not undermine the broader conclusions about who the leaders and laggards are.
From a policy perspective, these findings suggest two implications. First, top performers demonstrate institutionalized sustainability capacity, reflected in consistently strong results across methods. Second, mid-ranked universities are more volatile, which indicates that their future performance depends less on structural characteristics (e.g., size or type) and more on governance, strategic orientation, and the institutionalization of sustainability practices. This distinction between stability at the top and volatility in the middle has important consequences for policy design, particularly in guiding resource allocation and capacity-building initiatives.

4.3. Regression Analysis

We estimate linear models to assess which institutional characteristics are associated with sustainability engagement, measured by THE Impact. The baseline specification includes THE Education, GM-ED, log(Students), and a dummy for Private institutions; we report HC3 robust standard errors to accommodate heteroskedasticity. Here, log(Students) refers to the natural logarithm of student enrollment, applied to reduce skewness in the distribution and to allow regression coefficients to be interpreted in proportional rather than absolute terms. This modeling strategy allows us to move beyond descriptive comparisons and test whether institutional features exert systematic effects once controls are included.
Model A (main effects). Results (Table 5) indicate that GM-ED is a positive and statistically significant predictor of THE Impact, while THE Education is also positively associated, albeit with a comparatively smaller effect size. The coefficient on log(Students) is small and statistically indistinguishable from zero, suggesting that institutional scale, per se, is not a reliable driver of SDG-oriented performance once other factors are held constant. The Private dummy is not statistically significant, reinforcing earlier group comparisons that showed substantial within-type heterogeneity. Thus, sustainability outcomes appear more closely tied to curricular and research engagement than to structural capacity or ownership type.
Model B (interactions). To probe heterogeneity, we augment the baseline with Education × Private and GM-ED × log(Students) interactions (Table 6). Interaction terms are not statistically significant at conventional levels, and model fit improves only marginally (Table 5). Substantively, this implies that the positive association between GM-ED and THE Impact does not systematically vary by university size, and that the relationship between Education and THE Impact does not differ in a consistent way between public and private institutions. In other words, the drivers of sustainability performance are relatively uniform across types and scales of institutions.
Model fit and diagnostics. The explanatory power of the models is moderate (see R2 and Adjusted R2 in Table 7), consistent with the idea that governance and qualitative institutional factors—unobserved in our data—likely matter for sustainability outcomes. The regression analysis provides several important insights into the determinants of sustainability engagement in Turkish higher education. First, the results confirm that sustainability education efforts, as captured by the GM-ED indicator, are strongly aligned with SDG performance (THE Impact), even after controlling for teaching quality and institutional scale. This finding suggests that universities embedding sustainability into curricula, research, and student initiatives achieve more visible outcomes in global sustainability benchmarks. Second, teaching quality (THE Education) also shows a positive, though comparatively modest, association with sustainability impact, indicating that traditional academic excellence and sustainability engagement are related but not identical dimensions of performance. Finally, the coefficients on institutional size and ownership (public versus private) are small and statistically insignificant, implying that structural attributes alone do not explain differences in sustainability outcomes. In sum, these results reinforce the broader pattern observed in descriptive, comparative, and composite index analyses: it is the strategic integration of sustainability into education—rather than size or sector—that underpins stronger SDG-related outcomes in higher education. As a consequence, the regression confirms and strengthens the descriptive and composite index findings: strategic integration of sustainability into education is the primary driver of SDG-related visibility, not institutional form or size.

4.4. Cluster Analysis

To add to the regression and index results, we also ran a k-means clustering on the normalized scores of THE Education, THE Impact, and GM-ED. This unsupervised method groups universities with similar profiles, letting us see whether clear performance “archetypes” show up in the Turkish higher education system. Still, the clustering should be read as an exploratory exercise, not as a strict classification.
We evaluated solutions ranging from k = 2 to k = 6, using the elbow method and silhouette scores as diagnostic criteria. The elbow method examines how much additional explanatory power is gained when adding more clusters, while the silhouette score measures how similar each university is to its own cluster compared to other clusters. The optimal partition was obtained at k = 3, which balances within-cluster homogeneity with between-cluster separation. The average silhouette score for the k = 3 solution was 0.41, indicating moderate but interpretable cluster quality. The relatively modest silhouette score suggests that while broad patterns exist, overlaps across clusters remain considerable.
Table 8 summarizes the mean values of the three performance indicators for each cluster. The results suggest three broad institutional archetypes:
Cluster 1—High Performers: Universities with consistently high scores across all three dimensions, including well-established public technical universities such as Middle East Technical University and Istanbul Technical University.
Cluster 2—Sustainability-focused Institutions: Universities with strong GM-ED and THE Impact scores but comparatively modest THE Education performance. Several mid-sized public universities fit this pattern, investing in sustainability infrastructure and engagement even without top positions in teaching-related rankings.
Cluster 3—Low Performers: Universities with below-average scores across the board, typically smaller regional institutions with limited resources and lower international visibility.
The cluster analysis underscores the heterogeneity of Turkish higher education institutions but should be interpreted with caution. High performers represent integrated models of academic and sustainability strength. Mid-tier institutions illustrate that sustainability visibility can be achieved even without high teaching scores. Low performers reveal systemic constraints related to resources and governance. At the same time, overlaps across clusters indicate that clear-cut typologies are difficult to sustain, and institutional strategies may evolve over time. Therefore, clustering provides a complementary, illustrative lens rather than a definitive classification of Turkish universities.
Overall, the results point to a consistent pattern: while institutional size and ownership play a limited role, the integration of sustainability into education and research is strongly associated with higher SDG-related performance. In the next section, we discuss these findings in relation to the broader literature and their policy implications.

5. Discussion

The results of this study provide a multidimensional understanding of sustainability performance among Turkish universities and offer contributions to broader international debates. While institutional size and ownership appear to have little independent influence, the integration of sustainability into curricula and research emerges as the most consistent driver of SDG-related performance.
The main role of education in the SDGs has been emphasized since their adoption in 2015 [1]. As Fonseca et al. [2] argue, SDG 4 is interconnected with nearly all other goals, and universities have become essential actors in advancing this agenda [3,4]. Our results confirm this perspective. This means institutions embedding sustainability into teaching and research show stronger visibility in global sustainability metrics. In short, progress is uneven and context-dependent, as [8] observed in cross-national comparisons. Turkish universities reflect this global heterogeneity, with some achieving systemic integration and others displaying fragmented or symbolic adoption.
The strong association between GM-ED and THE Impact scores reinforces the importance of green education as a pathway to SDG engagement. This result is directly relevant to SDG Target 4.7, as it indicates that universities integrating sustainability into curricula and student engagement processes contribute to the advancement of the knowledge, skills, and values emphasized by this target. Prior research highlights that green education fosters critical awareness of global environmental challenges [24,25,26]. In addition to this, green education connects learning to institutional transformation [30]. Our findings show that Turkish universities investing in curricular and student engagement initiatives gain visibility in sustainability rankings, consistent with the arguments of Akinsemolu & Onyeaka [23]. At the same time, the weaker link with THE Education indicates that traditional teaching metrics and sustainability-oriented measures are not fully aligned—echoing the gap between symbolic commitments and deeper reforms identified by Gale et al. [37] and Weiss et al. [36].
Several strands of literature emphasize that sustainability integration is most effective when it is both participatory and systemic. Ceulemans et al. [16] underline the role of stakeholder engagement in program design, while Dagiliūtė et al. [35] highlight student participation as a driver of curricular change. Our regression analysis confirms that sustainability education (GM-ED) is a stronger predictor of SDG performance than institutional size or ownership, suggesting that reforms embedded in teaching and student life carry more weight than structural capacity alone. Studies in other contexts [32,33,34] similarly stress that without whole-institution approaches, sustainability efforts remain partial. The Turkish results illustrate this tension: while leading universities display integrated models, many mid-tier institutions risk symbolic adoption unless governance mechanisms align teaching, operations, and research [37].
The composite index analysis demonstrates that despite methodological differences across equal, PCA, and entropy weighting, the identity of top performers remains stable. This confirms earlier arguments that triangulation of indicators provides a more balanced view than reliance on single metrics [38,42,43]. Nevertheless, the weaker link between THE Education and sustainability scores echoes critiques that conventional rankings may privilege resource visibility over pedagogical transformation [39,40]. The volatility of mid-ranked universities further illustrates the risks of treating global rankings as definitive measures, as Kapfudzaruwa [9] and Stough et al. [41] caution. Our analysis thus supports Alberti et al. [31] in arguing that sustainability indicators should be used as diagnostic tools rather than absolute benchmarks.
Beyond the methodological implications, it is important to consider the role these rankings play in the Turkish higher education landscape. Turkish universities increasingly use THE Impact Rankings and UI GreenMetric as external visibility tools, and most institutions participating in sustainability initiatives report at least one of them in their official communications or sustainability reports. In this sense, these rankings act not only as assessment mechanisms but also as drivers of institutional behavior, shaping how universities frame their sustainability achievements. Among the available tools, THE Education (Teaching), THE Impact, and GM-ED are the most widely adopted and internationally recognized frameworks for Turkish universities, which justifies their use in this study. Nevertheless, the influence of these rankings remains uneven: while leading universities strategically align their curricula and research with ranking criteria, many others present symbolic reporting without systematic integration. Future studies could further triangulate ranking results with institutional sustainability reports to capture qualitative aspects that are not visible in quantitative indicators.
These findings have theoretical resonance. Sterling [7] poses the question of whether sustainability integration in higher education is an operational adjustment or a transformative learning process. Evidence from Türkiye suggests both dynamics: leading institutions such as METU and ITU represent transformative integration, while many others display fragmented or symbolic approaches. This duality reflects Veidemane’s [22] distinction between symbolic and structural adoption and supports Sebestyén & Abonyi’s [20] call for more integrative conceptual models. The Turkish case therefore contributes comparative evidence from a middle-income context, illustrating both the potential and the limits of sustainability reform in higher education systems under rapid expansion.
The Turkish higher education system is an interesting case because of its size, variety, and the way policy frames it in terms of global competitiveness [13]. Our results show that being large or private/public does not by itself mean better sustainability performance. This is in line with Acer and Güçlü’s [45] point that simply expanding structures does not guarantee quality. What really makes a difference is whether sustainability is built into the university’s teaching and research strategies. Similar concerns are raised by Atici et al. [11] and Akyol Özcan [12], who find growing interest among Turkish universities but also a lack of systematic alignment with SDG 4. Recent work by Göçoğlu [14] and Yılmaz Fındık and Erçetin [15] also stresses governance and equity, and our results support that emphasis.
Policy measures could build on these insights. Accreditation standards might explicitly require sustainability-related learning outcomes, while funding mechanisms could reward demonstrated progress in GreenMetric or THE Impact performance. Professional development for faculty could focus on embedding competencies such as systems thinking and collaboration [29]. Importantly, performance-based funding and rector evaluations could integrate SDG criteria to ensure that sustainability is institutionalized rather than treated as a peripheral initiative. In Türkiye’s context of rapid expansion, these measures could help align national higher education strategies with both global competitiveness and the UN’s 2030 Agenda.

6. Conclusions

In this paper, we have presented the first systematic, multidimensional assessment of green education in Turkish higher education. By integrating THE Education, THE Impact, and GreenMetric (GM-ED) with institutional characteristics, the study offers novel evidence from a middle-income context where empirical analyses have been scarce.
Three contributions stand out in our findings. First, green education, understood as the integration of sustainability into curricula, research, and student engagement, appears as the most consistent driver of SDG performance. Second, institutional size and ownership have little explanatory power, which shows that strategy and governance matter more than structural features. Third, while composite indices highlight stable leaders and more volatile mid-ranked institutions, the clustering results suggest a variety of pathways. In sum, these findings confirm that sustainability engagement is not uniform but shaped by context.
Theoretically, our study extends debates on whether sustainability in higher education represents symbolic adoption or transformative integration. Evidence from Türkiye shows both dynamics: top performers institutionalize green education, while others remain fragmented. This duality reinforces the need for whole-institution approaches and supports calls for integrative conceptual models [7,22,31].
For policymakers, the implications are clear: accreditation standards should embed sustainability learning outcomes, funding should reward measurable green education performance, and leadership evaluations should include SDG criteria. Such reforms would help move sustainability beyond symbolic projects and institutionalize it in universities’ core missions.
Future research should combine quantitative benchmarking with qualitative studies of governance and culture, employ longitudinal designs to capture institutional change, and extend comparative analyses across middle-income countries. Overall, the study demonstrates that advancing the UN 2030 Agenda in higher education depends less on structural scale and more on the institutionalization of green education as a transformative practice.

Funding

This research received no external funding.

Data Availability Statement

The data that support the findings of this study are derived from publicly available sources. The Times Higher Education (THE) World University Rankings and Impact Rankings can be accessed through the official THE website. The UI GreenMetric World University Rankings are available from the GreenMetric portal. National institutional data, including student enrollment and ownership status, were obtained from the Council of Higher Education (YÖK) and official university reports. Processed datasets used for statistical analysis are available from the corresponding author upon reasonable request.

Conflicts of Interest

The author declares no conflicts of interest.

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Sustainability 17 08800 g001
Figure 1. Boxplot of THE Impact by University Type.
Figure 1. Boxplot of THE Impact by University Type.
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Figure 2. Top 10 Universities by GECI-Equal vs. PCA vs. Entropy.
Figure 2. Top 10 Universities by GECI-Equal vs. PCA vs. Entropy.
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Table 1. Summary of selected indicators (by ranking).
Table 1. Summary of selected indicators (by ranking).
Ranking FrameworkIndicator Used (Study Variable)What It Captures (Per Source)Notes on Data Handling/Coverage
Times Higher Education (THE)—World University RankingsTHE Education (Teaching) scoreTeaching quality & academic environment; includes factors such as staff-to-student ratios, doctorate awards, teaching reputation survey results, and institutional resources.Used as reported from THE WUR as one of the three core performance indicators.
THE—Impact RankingsTHE Impact (overall) score (SDG engagement incl. SDG 4)Measures a university’s sustainability engagement through the UN SDGs; SDG 4 (Quality Education) is a key component for our purposes.Where results are reported in bands/ranges, midpoint values were calculated for comparability.
UI GreenMetric—World University RankingsEducation & Research (GM-ED) scoreAssesses integration of sustainability into curriculum design, research output related to sustainability, and student involvement in environmental initiatives.For context, each university’s 2024 GreenMetric global and national rank was also recorded in the dataset.
Table 2. Descriptive Statistics of Key Variables (n = 50).
Table 2. Descriptive Statistics of Key Variables (n = 50).
MetricMeanStd. Dev.MinMax
THE Education20.377.0311.144.2
THE Impact59.0617.6025.8593.2
GM-ED1373.9366.74001800
Students35,92019,434361570,466
Table 3. Correlation Matrix.
Table 3. Correlation Matrix.
MetricTHE EducationTHE ImpactGM-EDStudents
THE Education1.000.440.170.12
THE Impact0.441.000.540.21
GM-ED0.170.541.000.16
Students0.120.210.161.00
Table 4. Group Means by University Type.
Table 4. Group Means by University Type.
University TypeTHE EducationTHE ImpactGM-EDStudents
Public20.2258.281384.139,592
Private21.1663.121320.616,644
Table 5. OLS with HC3 Robust Standard Errors (Model A: Main Effects).
Table 5. OLS with HC3 Robust Standard Errors (Model A: Main Effects).
VariableCoefRobust SEtp-Value
Constant37.2148.5414.360.000
THE_Education0.3170.1292.460.018
GM_ED0.0210.0063.520.001
log_students−0.8440.671−1.260.214
Private2.1872.1081.040.304
Table 6. OLS with HC3 Robust Standard Errors (Model B: +Interactions).
Table 6. OLS with HC3 Robust Standard Errors (Model B: +Interactions).
VariableCoefRobust SEtp-Value
Constant35.6729.1843.880.000
THE_Education0.2980.1352.210.032
GM_ED0.0200.0073.010.004
log_students−0.7220.703−1.030.310
Private2.0562.2230.930.356
Edu_x_Private0.0410.0291.410.167
GMED_x_logStuv0.0000.000−0.880.383
Table 7. Model Fit Statistics.
Table 7. Model Fit Statistics.
ModelNR-SquaredAdj. R-SquaredAICBIC
A: Main effects500.4310.397276.3285.6
B: +Interactions500.4470.398277.1289.9
Table 8. Cluster Means for THE Education, THE Impact, and GM-ED.
Table 8. Cluster Means for THE Education, THE Impact, and GM-ED.
ClusterTHE Education (Mean)THE Impact (Mean)GM-ED (Mean)N (Universities)
118.8462.811487.9434
218.2335.30875.4511
335.4685.791695.005
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Sahin, B. Advancing Sustainable Development Goal 4 Through Green Education: A Multidimensional Assessment of Turkish Universities. Sustainability 2025, 17, 8800. https://doi.org/10.3390/su17198800

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Sahin B. Advancing Sustainable Development Goal 4 Through Green Education: A Multidimensional Assessment of Turkish Universities. Sustainability. 2025; 17(19):8800. https://doi.org/10.3390/su17198800

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Sahin, Bediha. 2025. "Advancing Sustainable Development Goal 4 Through Green Education: A Multidimensional Assessment of Turkish Universities" Sustainability 17, no. 19: 8800. https://doi.org/10.3390/su17198800

APA Style

Sahin, B. (2025). Advancing Sustainable Development Goal 4 Through Green Education: A Multidimensional Assessment of Turkish Universities. Sustainability, 17(19), 8800. https://doi.org/10.3390/su17198800

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