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Page 16 of 21 Özbek et al. Carbon Footprints 2025, 4, 30 https://dx.doi.org/10.20517/cf.2025.43

result expresses the minimum point at which the increase in income decreases the environmental quality in
the U interaction valid within the framework of the RKC hypothesis in the Indian economy.

The CCR robustness test estimates in Table 7 show that a 1% increase in GDP, GDP2, NREN, and TO
causes a 14.67% decrease, 1.05% increase, 0.48% decrease, and 3.48% increase in REN, respectively. These
effects occur at a 1% significance level in GDP, GDP2, and TO. The URB estimate is statistically
insignificant. In addition, it is concluded that the C and T terms are also significant in the estimate. As a
result, the Model-2 results testing the RKC model have shown that the RKC hypothesis is valid. According
to the CCR estimate, the turning point in the Model-2 results is obtained as = 6.98. Since this value
obtained is the elasticity coefficient, its equivalent in dollars is approximately $1,075. This result expresses
the minimum point at which the increase in income decreases the environmental quality in the U
interaction valid within the framework of the RKC hypothesis in the Indian economy.

Finally, the study focuses on short-term relationships. Understanding whether there is a causal interaction
between EF and REN variables and other variables in terms of both environmental degradation and
environmental quality can provide important predictions. In this context, the FBTY causality test proposed
[68]
by Nazlioglu et al. was used. The relevant results are presented in Table 8.

In Table 8, the existence of causality interaction of GDP, GDP2, NREN, TO, and URB variables toward EF
and REN was investigated. According to FBTY results, GDP, GDP2, and TO variables are the cause of the
EF variable at 1% significance level. On the other hand, GDP, GDP2, TO, and URB variables are the cause of
the REN variable at 1% significance level. These results obtained for FBTY short-term causality interaction
showed that long-term relationships were supported.

DISCUSSION
Discussion of findings and policy implications
The empirical results of this study offer significant insights into the environmental development trajectory
of the Indian economy. The primary finding - that the RKC turning point (at approximately $1,048 per
capita) precedes the EKC turning point (at approximately $1,729 per capita) - empirically confirms the
theoretical proposition of Yao et al. for a major developing economy. This outcome aligns with the
[10]
[13]
findings of Pata et al. for the US, suggesting that the initial shift toward renewable energy adoption is a
critical precursor to achieving a reduction in the overall ecological footprint. The implication for India is
that the foundation for environmental improvement is laid before the country reaches its peak pollution
level, creating a crucial policy window to accelerate this transition.

The finding that the RKC turning point occurs earlier also reveals a challenging dynamic: while renewable
energy use begins to increase, overall environmental pollution continues to rise until a much higher income
level is achieved. In other words, the positive environmental effects of renewable energy adoption are felt
with a significant delay. This lag underscores the persistent impact of NREN, which, as our results confirm,
remains a primary driver of the ecological footprint in the long run. The absence of a short-term causal
relationship from non-renewable energy to the ecological footprint in our FBTY test results further
strengthens this point, suggesting that environmental degradation is a cumulative, long-term process rather
than a short-term shock.

Regarding the control variables, the dual role of TO is noteworthy. Our findings indicate that TO not only
contributes to a reduction in the ecological footprint in the long term but also strongly promotes REN. This