4.1. Environmental Pressure Index (EPI) with PCA Method
In order to construct the Environmental Pressure Index in this study, the index variables were normalized using the Min–Max normalization method. In this approach, variables are normalized using the min–max procedure, which rescales each variable to lie within the [0, 1] interval. Following normalization, the eigenvalues of the variables were calculated. In Principal Component Analysis (PCA), eigenvalues indicate the proportion of information each variable contributes to the index. According to the Kaiser criterion, it is recommended to retain all factors with eigenvalues greater than 1. Any factor with an eigenvalue below this threshold is considered to explain less of the common variance and is therefore excluded.
Table 1 presents the eigenvalues and cumulative variance ratios of the variables included in the analysis.
According to the analysis results presented in
Table 1, two factors with eigenvalues greater than 1 were identified. The cumulative variance explained by these two factors is 67.63%. The cumulative variance ratio represents the proportion of total variance in the index explained by the retained components. Based on the findings, these two factors collectively account for 67.63% of the total variance. The eigenvectors (factor loadings) of the variables corresponding to each principal component are provided in
Table 2.
Eigenvectors are used to calculate the index weights. A positive eigenvector value indicates a direct relationship with the principal component (PC), whereas a negative value reflects an inverse relationship. According to
Table 2, the variables with the highest factor loadings in PC1 are, respectively: AIR (−67.73%), BIO (59.17%), and EF (43.10%). In PC2, the variables with the highest loadings are: GNP (83.44%), EF (43.38%), and BIO (−31.57%). The squared values of the eigenvectors represent the proportion of variance each variable explains within the corresponding principal component. In PC1, AIR explains 45.37% of the variance, while in PC2, GNP accounts for 69.62% of the variance. The primary directions of the index variables, based on the principal components, are illustrated in
Figure 2 as an Orthonormal Loadings graph.
According to
Figure 2, the variables biocapacity, ecological footprint, and gross national product (GNP) exhibit a positive relationship with one another within the index, whereas air pollution shows a negative relationship with these variables. Biocapacity reflects a region’s ability to produce renewable natural resources and is one of the key components used in the calculation of the ecological footprint. Therefore, a positive correlation between these two variables is an expected outcome. Likewise, the negative association between air pollution and these variables is also consistent with theoretical expectations. To enhance the interpretability and clarity of the principal components (PCs), a rotation procedure was applied. Rotation increases the factor loadings of variables without altering their underlying mathematical properties. In this study, the Varimax method, which is one of the most commonly used orthogonal rotation techniques, was employed. The results of the rotation are presented in
Table 3.
According to
Table 3, the rotation results show that in Factor 1, the variables contributing the highest factor loadings are AIR (−66.95%), BIO (59.99%), and EF (28.33%). In Factor 2, the highest contributors are EF (31.89%), NGNP (22.56%), and AIR (−13.42%). Similar to the orthonormal results, AIR continues to contribute negatively to the index. In the final stage of the PCA process, the weights of the principal component matrix were calculated. The method used to compute these matrix weights is presented in Equation (4).
The index weights of the variables were calculated by multiplying the previously computed cumulative variance ratios of the factors by the factor loadings of the respective variables. The resulting index weights are presented in
Table 4.
According to
Table 4, the variables with the highest factor weights in the index are, respectively: AIR (46.11%), BIO (37.96%), and EF (29.70%). Given that air pollution, biocapacity, and ecological footprint are core determinants of observed environmental pressure across countries, the relatively high weights assigned to AIR, BIO, and EF in the composite index are fully consistent with the underlying conceptual framework and empirical expectations.
4.2. Panel Analyses
Prior to the panel analysis, descriptive statistics of the variables to be used in the model were calculated. The descriptive statistics for both the dependent and independent variables included in the model are presented in
Table 5.
According to
Table 5, the mean and median values of the variables are relatively close to each other, indicating that the data are clustered around the center. The variable with the highest standard deviation is the urbanization rate, which is one of the control variables, suggesting that it has the widest distribution in the model. The kurtosis values range between 2.14 and 7.70, indicating that the distributions exhibit asymmetrical characteristics. Regarding skewness, most variables display positive skewness, meaning the distributions are left-skewed.
To detect the presence of multicollinearity in the panel model used in this study, both Spearman correlation analysis and Variance Inflation Factor (VIF) tests were conducted. High levels of correlation among variables may lead to biased or unreliable results in regression analysis. Therefore, variables that may cause multicollinearity should be excluded from the model. According to Gujarati [
62], a correlation coefficient above 0.80 among explanatory variables suggests the presence of multicollinearity. Hence, proceeding with variables having correlation values below this threshold is expected to yield more reliable results. In addition to correlation analysis, the VIF test is commonly used in the literature to detect multicollinearity. According to Curto and Pinto [
63], if the VIF value is equal to or less than 10, it indicates the absence of multicollinearity among the explanatory variables. The correlation matrix and VIF values are presented in
Table 6.
According to
Table 6, the highest correlation coefficient among the variables was calculated as 0.6677, observed between financial depth and technological innovation. The existence of a relationship between a country’s financial depth and its level of technological innovation is an expected result. Investment in innovation facilitates the development and diffusion of technological and innovative products. Meanwhile, financial depth plays a key role in effectively promoting innovation by reducing financing costs, allocating scarce resources efficiently, evaluating innovative projects, and managing associated risks. The fact that all correlation coefficients remain below the 0.80 threshold indicates that the model is not subject to multicollinearity. The VIF values reported in
Table 6 range from 1.0433 to 1.4141, further confirming the absence of multicollinearity. Therefore, all selected variables were retained in the model and included in the analysis.
Prior to conducting panel regression, diagnostic tests were carried out to determine the appropriate unit root tests and to ensure the validity of the selected regression methodology. Identifying the presence of cross-sectional dependence and heteroskedasticity among the variables is crucial for ensuring the accuracy and reliability of the empirical findings. When such conditions exist, the chosen analysis must account for them to avoid biased results [
64,
65]. The results of these diagnostic tests are presented in
Table 7.
According to the cross-sectional dependence test results presented in
Table 7, the p-values for the variables used in the model are less than 0.05, indicating the presence of cross-sectional dependence among countries. Additionally, the results of the heteroskedasticity test confirm the existence of heteroskedasticity within the model. Given the presence of cross-sectional dependence identified in the diagnostic tests, the study employed a second-generation unit root test—the CADF-CIPS test developed by Pesaran [
66]—instead of first-generation unit root tests for stationarity assessment. The null hypothesis (H
0) of the CADF-CIPS test states that “a unit root exists in the series.” If the p-values are less than 0.05, the null hypothesis is rejected, indicating that the series is stationary. The statistical values and
p-values obtained from the unit root tests are presented in
Table 8.
According to the CADF-CIPS test results presented in
Table 8, all variables used in the model have
p-values less than 0.05, indicating that the variables are stationary at the level. In other words, it has been concluded that the series does not contain unit roots. After confirming the stationarity of the series, Pedroni [
67] and Kao [
68] panel cointegration tests were conducted to determine the existence of a long-run relationship among the variables. The results of these tests are reported in
Table 9 and
Table 10, respectively.
According to
Table 9, the results of the Pedroni [
67] cointegration test, specifically the panel PP-statistic and panel ADF-statistic from within-dimension tests, as well as the group PP-statistic and group ADF-statistic from between-dimension tests, indicate that the null hypothesis of “no cointegration among the variables” is rejected. In other words, there is evidence of a long-run relationship among the variables. The results of the Kao [
68] cointegration test further support the findings of the Pedroni test by confirming the existence of cointegration among the variables.
In order to determine the optimal lag length, a Vector Autoregressive (VAR) model was employed. Based on the Akaike Information Criterion (AIC), the optimal lag length was identified as two lags. To decide between the use of the Pooled Mean Group (PMG) and Mean Group (MG) estimators, a Hausman test was conducted. According to the results presented in
Table 11, the null hypothesis of coefficient homogeneity could not be rejected, indicating that the PMG estimator is appropriate. Therefore, the PMG estimator was selected for the analysis. The short-run and long-run estimation results from the PMG-ARDL model are reported in
Table 11.
According to the PMG panel ARDL results presented in
Table 11, a statistically significant and positive long-run relationship is observed between the environmental pressure index and financial access. This finding indicates that higher levels of financial access are associated with increased environmental pressure in the long run. Conversely, financial depth and financial efficiency exhibit statistically significant and negative long-run associations with the environmental pressure index, indicating that higher levels of financial depth and financial efficiency are associated with lower environmental pressure over the long run. Additionally, technological innovation exhibits a statistically significant and negative long-run association with environmental pressure, indicating that higher levels of technological innovation are associated with reduced environmental pressure in the long run. Regarding the control variables, both urbanization and population growth are found to be positively and statistically significantly associated with environmental pressure in the long run, indicating that higher levels of urbanization and population growth correspond to increased environmental pressure. In the short run, the error correction term (ECT) is negative and statistically significant, indicating that deviations from the long-term equilibrium are corrected over time. The ECT coefficient is estimated at −0.95, implying that approximately 95% of the disequilibrium from the previous period is adjusted within the current period. Consistent with the long-run findings, the short-run results indicate a statistically significant and positive association between financial access and environmental pressure, suggesting that higher levels of financial access are associated with increased environmental pressure in the short run. These findings suggest that while increasing access to financial services facilitates the availability of instruments for individuals and firms, uncontrolled financial expansion may exacerbate environmental pressure. In contrast to the long-run findings, the short-run results indicate a statistically significant and positive association between financial depth and environmental pressure, suggesting that higher levels of financial depth are associated with increased environmental pressure in the short run. Taken together, the short- and long-run findings suggest a non-linear relationship between financial depth and environmental performance. In the short run, increases in financial depth are associated with higher environmental pressure, potentially reflecting scale effects whereby expanded financial activity initially facilitates energy-intensive production, consumption, and investment. However, in the long run, greater financial depth appears to contribute to improved environmental outcomes, consistent with a transition toward more efficient capital allocation, enhanced access to green financing instruments, and the diffusion of cleaner technologies. This pattern implies the presence of a U-shaped relationship, whereby financial deepening initially exacerbates environmental pressure but ultimately supports environmental sustainability once a certain level of financial development is attained. Furthermore, financial efficiency shows a statistically significant and negative relationship with environmental pressure in the short term, indicating that higher levels of financial efficiency are associated with lower environmental pressure. This finding suggests that improvements in financial efficiency contribute to reduced environmental pressure by increasing the allocation and use of natural resources. Unlike the long-run results, the short-run analysis indicates a statistically significant and positive association between technological innovation expenditures and environmental pressure, suggesting that higher levels of innovation spending are linked to increased environmental pressure in the short term. These results suggest that while R&D investments made during the transition to environmentally friendly technologies may initially increase environmental pressure, green innovation contributes to reduced environmental pressure in the long term. Taken together, these findings indicate a non-linear adjustment pattern in which technological innovation initially intensifies environmental pressure but gradually mitigates it over time as efficiency gains and low-carbon technologies diffuse. Regarding the control variables in the short-run model, urbanization is positively but not statistically significantly associated with environmental pressure, whereas population growth exhibits a statistically significant and positive association. These findings support the hypothesis that increases in urbanization and population growth raise energy demand, potentially increasing pollution and environmental degradation. The results of the Dumitrescu-Hurlin [
17] panel causality test are presented in
Table 12.
According to the panel causality test results developed by Dumitrescu and Hurlin [
17] and presented in
Table 12, there exists a unidirectional causality running from financial access to environmental pressure at the 1% significance level. This indicates that increases in financial access influence environmental pressure, whereas environmental pressure does not have a significant effect on financial access. The second causal relationship identified in the model is a bidirectional causality between financial depth and environmental pressure, also significant at the 1% level. This suggests that as financial depth increases, it may initially exert greater pressure on the environment. However, over time, it may contribute to reducing environmental pressure by allocating more resources toward sustainable investments. Conversely, increases in environmental risks may negatively impact financial depth by influencing investment dynamics and risk perceptions. The third causal relationship in the model is observed between financial efficiency and environmental pressure, with a bidirectional relationship significant at the 5% and 1% levels, respectively. The mutual interaction between financial efficiency and environmental pressure implies that the efficient allocation of financial resources and proper investment targeting affect environmental conditions, while environmental sustainability objectives, in turn, influence countries’ financial decisions. A fourth bidirectional causal relationship, significant at the 5% and 1% significance levels, was found between technological innovation and environmental pressure. This reciprocal relationship indicates that environmental threats and risks stimulate technological advancement, while technological innovation contributes to environmental transformation and sustainability. Regarding the control variables, the analysis reveals a bidirectional relationship between urbanization and environmental pressure, and a unidirectional relationship from population growth to environmental pressure. These findings suggest that unplanned and rapid urbanization can increase environmental pressures, while environmental pressure may also influence urban expansion patterns. Furthermore, population growth is found to drive environmental pressure, likely due to increased energy demand, pollution, and ecological degradation.