The effect of energy consumption on the environment in the OECD countries: economic policy uncertainty perspectives.

In this paper, we investigate the impact of energy use and economic policy uncertainties on the environment. To achieve this objective, we use the pooled mean group-autoregressive distributed lag methodology (PMG-ARDL) and Dumitrescu and Hurlin causality test on 22 Organisation for Economic Co-operation and Development (OECD) countries between 1985 and 2017. The PMG-ARDL estimation shows that energy use and economic policy uncertainties have a positive relationship with carbon dioxide emission (CO2) emission, while a negative relationship is confirmed between renewable and CO2 emissions in the long run. The short-run estimation shows a positive relationship between energy use, real gross domestic product, and per capita on CO2 emissions. The Dumitrescu and Hurlin causality results highlight a unidirectional running from real GDP and GDP per capita square to CO2 emissions. Furthermore, one-way causality exists between CO2 emissions to economic policy uncertainties. These results have policy implications on the macroeconomy which are discussed in detail in the concluding section.

Introduction

Carbon emissions and the aftermath of non-renewable energy consumption have been on the increase since the beginning of the twentieth century at the global level. This is evidenced by emission figures that are 1.6 times the 1990 level leading to an excess of 36 billion tons in the year 2014 (Yao et al. 2019; Ozcan and Ozturk 2019; Rafindadi and Ozturk 2017). The share of fossil fuel energy of over 80% of the total energy supply (IEA 2016) and a considerably lesser than 20% renewable energy consumption rate all points to and corroborates the previous stance that rising carbon emission or energy consumption as the case may be is a direct result of economic growth. This, according to Grossman and Krueger (1995), would initially lead to an initial phase of environmental degradation, which is subsequently followed by the improvement phase as the average income increases on the environmental Kuznets curve.

Furthermore, Panayotou (1993) posited earlier that carbon emission would have three resultant effects: scale, structural, and technical effects stemming from economic growth, thus demonstrating and attesting to the inverted U-shaped Kuznets curve. Previous studies regarding carbon emissions, a resulting consequence of non-renewable energy consumption, and the environmental Kuznets curve hypothesis revolved mostly around international trade, technical progress, foreign direct investments, and incomes (Kaika and Zervas 2013; Yao et al. 2019; Sarkodie and Strezov 2019; Asongu and Nwachukwu 2018a & Asongu and Nwachukwu 2018b; Asongu and Odhiambo 2019b; Rjoub et al. 2021).

More recently, the addition to the group of information on the energy literature has been on renewable energy consumption and cleaner energies going by the outcry of the effects of an earth-wide temperature boost brought about via carbon outflow (Yao et al. 2019; Bekun et al. 2019a). This has led to the renewable energy environmental Kuznets curve (RKC) proposition as a hypothesis that supersedes the conventional environmental Kuznets curve in that it accounts for renewable energy to show the U-shaped relationship that exists between the renewable energy consumption rate and per capita GDP. This unconventional phenomenon, the RKC, asserts that more renewable energy consumption can help accelerate the conventional EKC to arrive faster at its turning point. This lends credence to the fact that the consumption of renewable and non-renewable energies will lead to a renewable environmental Kuznets curve that arrives faster at its turning point than an environmental Kuznets curve designated to non-renewable energy consumption. This has led to the selection of a renewable energy consumption rate, an index to uncover the differences of renewable energy consumption while examining the environmental Kuznets curve hypothesis side by side with the renewable energy environmental Kuznets curve hypothesis.

Economic policy uncertainty shows the relative frequency of specific news media references dealing with occurrences as they pertain to economy, policy, and uncertainty; government charge code arrangements that are due to expire; and the rate of forecaster disagreement. This uncertainty measurement ranges from the Global Economic Policy Uncertainty index value to the National Economic Policy Uncertainty index value Baker et al. (2016). It merely indicates the risk that comes with an uncertain policy response on the part of the government as an economic agent to put regulatory measures in place. This ultimately leads individuals and firms to become irresolute, thus delaying consumption and investment until the uncertainty is resolved. EPU has been on the increase since the 2007 to 2009 recession due to the observed uncertainty by households and businesses on fiscal policies, future taxes, spending, health care, monetary policies, and other measures in place to regulate the economy.

An increase in the EPU index often leads to the postponement and reduction of business and economic activities such as recruitment, investment, and other forms of spending. It was also discovered that policy uncertainty in news articles revolved around taxes, spending, and monetary and regulatory policies. This study harnesses to paint a picture of the linkage effect between policy uncertainty energy emission nexus and the environmental Kuznets curve hypothesis. While previous studies appeared to have neglected the link between carbon emissions, Jiang et al. (2019) posited that EPU most certainly affects the external business environment, which ultimately affects the decision-making process of economic agents. This trickles down on the carbon emissions as it is closely linked to the output decisions of microeconomic agents. As an OECD country, the USA is said to maintain a fairly stable and consistent EPU index. At peak periods of the US EPU index, for example, the total carbon emission is observed to replicate the local peak, and when the EPU index falls, the total carbon emission falls as well. The effect is a shift in the priority of the governments from environmental governance to the root cause of events that led to an increased financial policy uncertainty index in the first place. For example, the USA’s withdrawal from the Paris Agreement will increase the EPU index, leading to a lower prioritization of carbon emission reduction as a goal Jiang et al. (2019). Going by this analogy, one can infer that the EPU will have a corresponding effect on the postulation of the environmental Kuznets curve hypothesis because the EPU will readily affect production and consumption activities associated with renewable and non-renewable energies (Jiang et al. 2019). This leads to decreased investments or consumption at periods of high uncertainty and increased investments or consumption at periods of low uncertainty. Therefore, this attributes a low EPU to a quick arrival at the turning point of the environmental Kuznets curve and a high EPU to points farther away from the turning point of the environmental Kuznets curve.

Research conclusions from previous studies lend credence to the fact that EPU is relevant to understanding the behavior of emissions in energy consumption even at the global level. This is because the EPU impacts macroeconomic activities, which has a ripple effect on societal carbon emissions across countries. Observing the USA’s economy, an OECD country that happens to be the second-largest carbon emission country in the globe, it is important to study the linkage effect of the economic policy uncertainty in relation to energy emissions to understand the appropriate actions to be taken for periods of high economic policy uncertainties especially as they relate to the environmental Kuznets curve hypothesis which is the objective of this research work. In summary, this study draws strength from the carbon-income function and EKC framework for OECD countries that have received little or no documentation in the energy-environment literature while accounting for economic policy uncertainty on the environment. The next segment presents a survey of the literature review of related studies. This is followed by a description of data, variables, and methodology in the “Data and methodology” section. The “Results and discussion” section presents the empirical results from this study and discusses the implications of the research findings. This study concludes in the “Conclusion and policy implications” section with vital energy and macroeconomic policy recommendations.

Literature review

A lot of studies have investigated the relationship between energy consumption and economic growth across countries and across regions (Al-Mulali et al. 2016; Ozturk and Bicimveren 2018; Udemba et al. 2020; Adedoyin et al. 2020a, 2020b; Kirikkaleli et al. 2020; Udi et al. 2020; Tchamyou et al. 2019; Asongu and Odhiambo 2019a). Some of these studies examined variants of growth-energy nexus, energy-growth nexus, and the two-way causal effect between them. Starting with an earlier trajectory by the OECD in 2011, it was predicted that the share of energy consumption allotted to the OECD group from the world consumption was set to reduce from 35% in 1995 to about 32% by 2020. Prior to this point, the literature on economic growth and energy consumption dates as far back as 1978, following a seminal work by Kraft and Kraft on the relationship between energy and Gross National Product. A handful of studies have concentrated on the relationship between economic growth and energy consumption in OECD countries (see Wong et al. 2013; Coers and Sanders 2013; Bella et al. 2014; Mercan and Karakaya 2015). For instance, Asongu et al. (2017) explored the determinants of environmental degradation in selected 44 sub-Saharan African countries using generalized method of moments techniques to explore the role of ICT modulates the effect of CO2 emissions on inclusive development. The study found that ICT can be used to reduce the negative effect of CO2 emission on inclusive development. That is, ICT modulating policy thresholds should be established for environmental sustainability targets in the selected African bloc.

Using autoregressive distributed lag model (ARDL) in conjunction with (FMOLS) and dynamic ordinary least squares (DOLS) for robustness, Adebayo et al. (2021) explored the nexus between environmental quality and economic growth while accounting for financial development and globalization for the case of South Africa. The study revealed that a 1% increase in energy (coal) consumption increases environmental degradation by 1.077%, while a 1% increase in financial development decreases the environmental degradation by 0.973%. The study submits that policymakers and administrators in South Africa should advance policies that encourage energy consumers to shift toward renewable energy. Furthermore, financial reforms should be implemented to reduce environmental degradation. This study is in line with Adebayo and Odugbesan (2021) study that financial development, economic growth, and urbanization contribute to the pollution level in South Africa.

Zhang et al. (2021) explored the anthropogenic effect of human activities on CO2 emissions using the STIRPAT framework. The study explored the determinant of CO2 emissions in Malaysia using ARDL, fully modified OLS (FMOLS), dynamic ordinary least square (DOLS), and wavelet coherence and gradual shift causality. The study regression shows that economic growth, gross capital formation, and urbanization positively impact CO2 emissions. The direction of causality reveals a one-way causality from urbanization to CO2 emissions, unidirectional causality from economic growth to CO2 emissions, and unidirectional causality from gross capital formation to CO2 emissions as reported by causality analysis. This outcome resonates with the study of Kirikkaleli et al. (2021) for the case of Turkey.

He et al. (2021) investigated the role of consumption-based carbon emissions in Mexico while accounting for the role of economic growth trajectory admits global trade flow, energy consumption using an autoregressive distributed lag approach, and a causality analysis frequency domain causality tests. The study’s key findings highlight that globalization and financial innovation improve environmental quality. Also, energy consumption and economic growth dampen environmental quality. Finally, trade openness exerts no significant impact on environmental quality. The study further illustrates the need for Mexican government officials to carefully craft energy environmental policies aimed at increasing economic growth without compromise for environmental quality.

Furthermore, regarding consumption-based carbon emissions determinants, Kirikkaleli and Adebayo (2021) for Indian identify that public-private partnership investment in energy and energy consumption also significantly causes consumption-based carbon dioxide emissions at different frequency levels in the Indian economy. While a causal relationship is said to be theoretically possible and already established as a stylized fact from these studies, discrepancies in these previous studies were traced to differences across countries, time skylines, informational collections, and factual techniques employed to determine the relationship between energy consumption and economic growth. These studies presented inconclusive results that were not fit for policy actions in OECD countries. Methods that were used by these studies ranged from vector error correction model, PVAR, autoregressive distributed lag model, DOLS, and FMOLS to explore the relationship in an attempt to explain the energy consumption-economic growth nexus, although some studies have used the panel data approach.

More recently, attempts have been made to advance the knowledge horizon of the energy literature as it pertains to OECD countries to understand and assert the direction and magnitude of the causal relationship between economic growth and energy consumption. Gozgor et al. (2018) examined the impact of renewable and non-renewable energy consumptions on growth using 29 OECD countries from 1990 to 2013. The study theoretically built a growth model to capture economic complexities and as a yardstick of capabilities amongst the countries in question. The study employed the panel autoregressive distributed lag due to the mixed nature of the sets of joining of the factors in question and the panel quantile regression methods for estimation. The study concluded that the positive effect of both renewable and non-renewable energy consumption components on economic growth was valid when checked against the growth hypothesis that the study adopted. The study, therefore, adopts the stands on the fact that energy consumption positively affects growth and that both renewable and non-renewable energy consumption is vital and important for the furtherance of economic growth. Additional studies like Jebli et al. (2016) investigated the relationships between monetary development, inexhaustible and non-sustainable power source utilization, carbon emissions, and international trade amongst 25 OECD countries over the 1980 to 2010 timeline. The study employed the granger causality tests, fully modified ordinary least squares, and the dynamic ordinary least squares. The study found that bidirectional causality existed between renewable and non-renewable energy consumption. The results also verified the inverted U-shaped environmental Kuznets curve hypothesis for the OECD countries in view. The study concluded that increased non-renewable energy consumption led to increased carbon emissions and that increased trade through renewable energy consumption measures to be considered to reduce environmental degradation.

A study by Kahouli (2019) assessed the relationship between the consumption of energy and growth of the economy across 34 OECD countries over the 1990 to 2015 timeline. The study employed an extensive and more recent panel data econometric method by using the static and dynamic techniques simultaneously and separately to look at the relationship between economic growth and energy consumption. The study found a unidirectional relationship between energy consumption and economic growth. Also, there was a one-way causal relationship running from economic growth to energy consumption under the dynamic estimation technique. This study was in line with earlier results by Salahuddin and Gow (2014), Omri and Kahouli (2014), Raza et al. (2015), and Kasman and Duman (2015), stressing the importance of the bidirectional relationship between energy consumption and economic growth.

More recently, the empirical study of Ozcan and Ozturk (2019) investigated the different linkages that exist between the use of energy and economic growth by taking a sample of 35 OECD countries over the 2000 to 2014 period. The study used three empirical models to capture the relationship between energy consumption, economic growth, and environmental degradation using the generalized method of moments and the panel vector autoregressive regression method. The study’s key contribution to the body of knowledge was a more encompassing proxy to capture environmental degradation. It employed two composite indices and the CO2 emission proxy used by earlier studies. In addition to the components of what appears to be an encompassing proxy than earlier studies, Ozcan and Ozturk (2019) collectively adopted the ecological footprint and environmental performance index to reflect the different forms of environmental pollution. The study found a significant positive relationship between economic growth (GDP) and energy consumption on all the environmental degradation indicators used as a proxy in the model. The study further indicated that increment in industrial economic activities of the countries in view contributed more to environmental pressure and CO2 emissions, which appeared to follow the general consensus.

Nevertheless, while there appears to be a paucity of literature in this variable combination, especially in the case of OECD countries, quite a few papers have provided a base knowledge of how the economic policy uncertainty impacts key sectors typical economy. However, one thing that comes to the fore is that corporations and economies are known to act conservatively at times of uncertainty, which slows investment activities and employment rates down. This ultimately affects the energy consumption variable of such an economy, which ultimately trickles down to other countries due to the interconnectedness that the world operates with.

Complexity is one factor responsible for the degree of uncertainty. An advancement that appeared to have eased this complexity is the innovation propounded by Baker et al. (2016), which established the economic policy uncertainty index. Prior to this point, an initial publication by Kenneth Galbraith in 1977 titled “The Age of Uncertainty” paved the way for what has now become a transformed research area. Overall, the conclusion from previous studies lent credence to the fact that more conservative policies were best at times of high economic policy uncertainty. This is because the cost of borrowing increases, making firms spend less on capital, leading to an economic downturn (Al-Thaqeb and Algharabali 2019).

Jens (2017) sought to understand the US gubernatorial decisions as a plausible source for exogenous variety in an attempt to investigate the link between political vulnerability and firm speculation. The study employed term confines as an instrumental variable for political decision closeness in addition to summary statistical methods to present the results. The study found that investment declined 5% before elections and rose as much as 15% for firms directly related and susceptible to this type of uncertainty. Also, because close elections are tantamount to periods of economic downturns, close election effect on investment was understated by more than half going by the ordinary least square method, and post-election rebounds to investment or consumption depended on the re-election of an incumbent administration. The implication for energy consumption is that high periods of political uncertainty will come with low energy consumption and the alternative sources of energy being considered at this period to determine the rate of environmental degradation for any typical OECD economy.

Canh et al. (2019) investigated the role of two forms of uncertainties: internal (domestic) economic policy uncertainty and the world uncertainty played on the net inflow of outside direct speculation in 21 countries the 2003 to 2013 timeline. The study adopted a sequential two stages linear panel data model technique to carry out its analysis. The study found that the domestic growth rate of the economic policy uncertainty index affected the inflow of foreign direct investments adversely. When this domestic growth rate was placed side by side with the growth rate of the World Uncertainty Index, a measure that accounts for 143 countries, the ensuing result was a positive impact on the net inflow of foreign direct investment to the host country in question. The study, therefore, concluded that while an increase in national economic policy uncertainty might present an adverse effect on FDI inflows, an increase in the world global economic policy uncertainty could lead to increased inflow of foreign direct investment, and this was explained as the behavioral bias that could averse an investor based on the investor’s sensitivity to factor in uncertainty when making an investment decision.

Zhang et al. (2019) investigated the influence of two key countries, the USA and the Republic of China, on several markets across the globe. The markets considered under this study were, namely, commodity, energy, credit, and financial markets. The study was borne out of the uncertainty that ensued from the US-China trade conflict and, thus, sought to provide answers to research questions around the rationale behind the conflict, the supposed threat that a rising Chinese economy could possibly be imposing on the US economy. The paper employed the economic policy uncertainty index of these two global players as a measure of their policy positions to build a time series that could estimate the degree of influence of the two countries on the global markets. The study found that while China’s realm of influence has increased in recent years, it has not been sufficient to oust the USA to control global world affairs. In addition, the study concluded that China’s competition with the USA in shaping the world is more politically driven rather than economically driven.

Liu et al. (2020) investigated the differential impact between investments in non-renewable and renewable energy enterprises. The study was comparative based on regulatory effects such as ownership concentration, external demand, financing constraints, growth opportunities, and how it related to investment and economic policy uncertainty. The study used data from 52 non-renewable energy enterprises and 116 renewable energy enterprises in China over the 2007Q1 to 2017Q4 timeline. The study employed a panel regression model for estimation. The study found that non-renewable energy enterprise investments were significantly inhibited by economic policy uncertainty.

On the other hand, renewable energy investments were not significant even though they were inhibited by economic policy uncertainty. The study also found that economic policy uncertainty specifically inhibited investment in the petroleum and coal enterprises, whereas economic policy uncertainty promoted investments in renewable energy enterprises like geothermal energy, solar energy, and other forms of renewable energy. The study concluded that growth opportunities could offset the inhibitory effect associated with the economic policy uncertainty and that a strengthened financial constraint brings with it an uncertainty associated with economic policy in non-renewable energy enterprise, which would not be as significant as the renewable energy enterprise.

Conclusively, the reviewed literature appears to have established a negative relationship between economic political uncertainty and energy consumption in that higher values of uncertainty reduce consumption and investment generally, but this sometimes leads to the consumption of cheaper and more traditional sources of energy which might, in turn, lead to increased carbon emissions thus increasing environmental degradation and extending the turning point of the environmental Kuznets curve.

Main gap and research contribution

One of the issues that commanded attention in the literature on economic uncertainty was the increased EPU value that came with the USA’s withdrawal from the Paris Agreement of 2015 to mitigate climate change. The importance attributed to environmental governance by the US government was reduced and reprioritized following this withdrawal, which negatively affected the implementation of a significant portion of previous environmental protection policies. This then became the testament on which the government’s determination to reduce carbon emissions as a goal became compromised. The ultimate implication of this move by the US government was that the Environmental Protection Agency’s budget had to be cut down in 2017. Secondly, the EPU was assessed to have been a possible threat to the US economy as a whole.

On the one hand, energy consumption by the US economy was cut down, making way for a decrease in carbon emission. On the flip side, a bad economic scenario for firms and the citizenry may opt for traditional cheaper sources of energy such as coal, which would result in more carbon emissions. Finally, facing high EPU, firms relaxed their effort to deliver an economy with reduced carbon emissions. This was due to the premonition that governmental departments would relax their requirements on environmental governance.

Another issue that suffices as a case for economic policy uncertainty is the decision by the UK to leave the European Union. While policies that are likely to be adopted by the European Union membership are uncertain, speculations about this uncertainty, especially in this transition period and with world events like the Coronavirus pandemic, have further increased uncertainty in the UK economy. A study by Steinberg (2019) sought to explore the macroeconomic impact of the trade policy uncertainty resulting from the Brexit movement. The study employed the dynamic stochastic general equilibrium (DSGE) model on the UK, the European Union, and the rest of the globe to address quantitative questions on the consequences of Britain exiting the European Union. Questions surrounding the uncertainty of the trade policies that were likely to replace the EU agreement post-Brexit and what the future held for the UK economy, as well as the lag periods that the turn of events as was to last for, were investigated by this study. The study found that uncertainty about Brexit will have little impact and that the welfare cost about Brexit is insignificant as households would sacrifice little to avoid this uncertainty. The study also found that the cost of Brexit, when compared with some other macroeconomic uncertainties, had a sizeable impact than other uncertainties meaning that a one-time Brexit uncertainty is the same as other unpredictable policy uncertainty in economic activity that occurs in the UK in an atypical year.

In summary, global and national issues have been identified as inflexion points that determine the degree of economic policy uncertainty. This is because the EPU index has its major components built on disagreements by forecasters, news references, and tax provisions, all of which are channels of speculation for economic agents, based on the highlighted literature and motivation in the “Introduction” section. The present study is further motivated by the United Nations Sustainable Development Goals (UN-SDGs 7, 8, and 13) crusade, which informed the choice of the variables for the econometric modeling, and subsequently, the following hypotheses have been constructed:

H1: Do conventional energy consumption (fossil fuel induced) engenders sustainability in the environment in the OECD countries in line with (UN-SDGs 7 and 8). Conventionally, energy use has been identified as a key driver for increased economic growth over the years. This proposition has been validated by several studies empirically, the first by Kraft and Kraft (1978) and more recently by several other studies affirming the pivotal role of the energy-induced growth hypothesis (Zakari et al. 2021; Emir and Bekun 2019; Bekun et al. 2019b; Asongu et al. 2017). This leads to the formation of the next hypothesis

H2: Is there a positive or negative nexus between CO2 emissions and economic growth in the study areas (OECD countries). There has been extensive literature on the economic growth-pollution connection. This is a result of increased dirty economic activities that will increase pollution emissions. This is in accordance with the fight of the UN-SDG 13 in mitigating climate change/pollution-related issues.

H3: Given the cointegration relationship establish between real income (GDP, CO2 emissions, and energy use). What is the connection between EPU in the mix for OECD countries over the sampled period?

Data and methodology

Data

The data are collected for 22 OECD countries spanning the period from 1985 to 2017. The selections of these countries are motivated by the amount of data available for all the variables under consideration. Data were extracted from the World Bank Development Indicator (WDI) and British Petroleum Database, which is given as CO2 emissions (CO2) measured in million tonnes of carbon dioxide (source: BP Statistical Review of World Energy June 2019); primary energy consumption (ENU) measured in million tonnes oil equivalent (source: BP Statistical Review of World Energy June 2019); real gross domestic product (RGDP), measured in constant 2010 US$ (source: WDI); and economic policy uncertainty1 (EPU), proxy: world uncertainty index (WUI) (source: Ahir et al. 2018, http://www.policyuncertainty.com).

Model and methods

This paper examines the role of economic policy uncertainties in the energy emissions consumption nexus in OECD countries. Hence, our energy emission function is set to include economic policy uncertainties. Methods like Pesaran’s test of cross-sectional independence, results of Pedroni and Kao cointegration tests, PMG-ARDL, and Dumitrescu and Hurlin panel causality were adopted.

where CO2 represents carbon dioxide emission, ENU measures the level of energy use, RGDP is a real gross domestic product, RGDP2 is GDP per capita, and EPU measure economic policy uncertainty, i, subscripts ei refers to each country’s fixed effects, that is, the countries and the time, as shown by the subscripts i (i = 1, −  − N) t (t = 1, −  − T), respectively.

Results and discussion

Table 1 provides a summary of the results for 22 OECD countries for the period 1985–2017. The emission of energy consumption, real GDP, and GDP per capita indices exhibit an increasing effect between 1985 and 2017, with real GDP having the highest increasing value of 11.7159% and energy use contributing to the lowest at 1.8260%. However, the economic policy uncertainty and economic policy uncertainty vs energy use indices have negative values, showing a decline of −1.4513% and −2.6249.

Table 1

Summary statistics (1985–2017)

Variables	OBS	Mean	Std. Dev	Min	Max
CO2	717	2.1433	0.7365	0.2726	3.7679
ENU	717	1.8260	0.6902	0.1695	3.3644
EPU	717	−1.4513	0.4041	−3.3685	−0.5199
EPU*ENU	717	−2.6249	1.2284	−7.7627	−0.2798
RGDP	717	11.7159	0.7049	9.8467	13.2393
RGDP2	717	4.5041	0.2562	3.6719	5.0491

Table 2 reports unconditional correlations on the selected variables for the 22 OECD countries. The correlation results show that carbon dioxide emission (CO2) is positively trending with the real gross domestic product (RDGP), economic policy uncertainty (EPU), and energy use (ENU). At the same time, it is negatively related to real domestic product per capita (RGDP2). These correlations suggest that carbon dioxide emission (CO2) is highly associated with the real gross domestic product, economic policy uncertainty, energy use, and real gross domestic product per capita. Every one of these estimations is measurably critical at 1%, 5%, and 10% levels, respectively. However, we further confirm their association in the following empirical investigation.

Table 2

Correlation matrix

	CO2	RGDP	RGDP2	EPU	ENU	EPU*ENU
CO2	1.0000
RGDP	0.9654***	1.0000
RGDP2	−0.1031***	0.0513	1.0000
EPU	0.0664**	0.1194***	0.1263	1.0000
ENU	0.9753*	0.9733***	−0.0365	0.0906***	1.0000
EPU*ENU	−0.7582	−0.7263	0.0891	0.5309	−0.7669	1.0000

Notes: The unconditional correlation was estimated using “natural log” data; ***, **, and * show a level of significance 1%, 5%, and 10%, respectively

Pesaran’s test of cross-sectional independence

In most of the empirical literature, panel data are often not tested for cross-sectional reliance among the series. While neglecting this fact posed severe implications to the analysis, the results obtained often remained unrealistic. Given this fact, it is essential to check the data set if they are cross-sectional reliance or independent. To do this, we applied the Pesaran (2004) cross-sectional dependence (CD) test on the 22-panel data. The results of the cross-sectional dependence (CD) test are reported in Table 3. The discoveries over the arrangement and economies propose that the invalid speculation of cross-sectional autonomy is dismissed at the 5% noteworthiness level, in this manner tolerating the elective theory. Consequently, these outcomes show that the chose information arrangement is a cross-sectional ward during the investigation time frame, 1985–2017.

Table 3

Cross-sectional dependency result

Test	Statistic	Prob.
Pesaran’s test of cross-sectional independence	2.189	0.0286**

Note. Null hypothesis: cross-sectional independence (CD ∼ (0.1). Prob

Stationary and cointegration tests

According to Baltagi et al. (2005), a panel data approach provides superior, robust findings, helping to increase the power of the unit root and cointegration test, given that it combines both time series and cross-sectional dimension (Brambor et al. 2006; Tchamyou and Asongu 2017; Boateng et al. 2018; Tchamyou 2019. The results in Table 3 above confirmed the presence of cross-sectional dependence across the series; hence, we apply a CIPS panel unit root test that considers cross-sectional dependence in the estimation. Specifically, we use the Bailey et al. (2016) cross-sectional augmented IPS (CIPS) test. The estimated results from the CIPS test are displayed in Table 4. The CIPS test the discoveries on level information arrangement over the factors, and economies propose the proof of a unit root. Be that as it may, the evaluations on the primary request distinction information arrangement affirmed the dismissal of the invalid theory at a 1% level of noteworthiness for the entirety of the examples and acknowledged elective speculations. This proof infers that the chose factors are not stationary at the level yet stationary at their first-request contrast.

Table 4

Results of unit root tests

Test	IPS
Variable	Level	First different
CO2	−1.846	−5.306***
RGDP	−2.143	−3.430***
RGDP2	−2.167	−3.465***
EPU	−3.670***	−6.114***
ENU	−1.927	−5.393***
EPU*ENU	−3.470***	−5.983***

Notes: CIPS (Pesaran, 2007); Methodology; *** and ** show the rejection of the null hypothesis, at 1% and 5% significance levels, respectively

Having confirmed that the series is stationary, we further proceed to check if the variables have a long-run relationship. To do so, we applied the Pedroni and Kao cointegration test and the result in Table 5. The results confirmed the rejection of the null hypothesis, which says there is no cointegration. Therefore, we accept an alternate hypothesis which says the series are cointegrated at a 1% significant level. This enables us to perform the PMG-ARDL analysis.

Table 5

Results of Pedroni and Kao cointegration tests

Statistic	Statistic	Prob
Pedroni cointegration test
Panel v-statistic	−0.1296	0.3561
Panel Rho-statistic	0.1125	0.4804
Panel PP-statistic	−3.49	0.0000***
Panel ADF-statistic	−4.35	0.0050***
Group Rho-statistic	1.487	0.8541
Group PP-statistic	−4.0118	0.0289***
Group ADF-statistic	−1.368	0.0113***
Kao cointegration test
	t-Stat	Prob.
ADF	2.6040	0.0181***

Note: Pedroni (2004, 1999). *** and ** represent a statistical rejection level of the null of no cointegration at a 1% significance level, respectively

Results of PMG-ARDL

Having established the series to be cointegrated in the long run, we further analyzed the PMG-ARDL test, as shown in Table 6. The long-run estimation confirmed that energy use and economic policy uncertainty has a positive relationship with CO2 emission value at the 1% and 5% significance level, respectively. This relationship means that only the energy use and economic policy uncertainty rise can lead to an increase in CO2 emissions with an average value of 1.1843% and 0.0199%, respectively. On the contrary, real GDP and GDP per capita improve CO2 emissions in these countries, with an average of 0.2023% and 0.3640, respectively. This is possible as more income is allotted to the individual, and such clean energy technologies became affordable. Therefore, renewable energy or clean energy technology consumption increases and reduces the level of CO2 emissions.

Table 6

Result of PMG-ARDL (1,1,1,1,1)

Variables	Model 1	Model 2	Model 3
Short run
ECT (−1)	−0.1137***	−0.0960***	−0.0759*
ENU	0.7277***	0.7513***	0.7513***
RGDP	0.2482***		−0.2267
RGDP2		0.2368**	0.4823
EPU	0.0003	0.0011	0.0608
EPU*ENU			0.0382
Long run
ENU	1.1843***	1.3455***	0.8559***
RGDP	−0.2023***		0.4469***
RGDP2		−0.3640***	−0.7887***
EPU	0.0199**	0.0142*	−0.0208
EPU*ENU			0.0094

Notes: ***, **, and * show the rejection of the null hypothesis at 1%, 5%, and 10% significance levels, respectively

The error correction term (ECM) coefficient that presents the speed of adjustment for the case of disequilibrium in the present study case is negative as expected and low (0.1137) at the 1% significance level. The ECM suggests that over 11% of the equation fit system is corrected for on an annual basis with the contribution of the study explanatory variables. The short-run estimation indicated that the values of energy use, real GDP, and GDP per capita positively influence CO2 emissions because they increase this variable by 0.7277%, 0.2482%, and 0.2368%, respectively. However, economic policy and the interrelated economic policy and energy use do not show any connecting relationship with CO2 emissions. Overall, energy use and economic policy positively affect CO2 emissions, while real GDP and GDP per capita reduce the increases in the 22 OECD countries.

The FMOLS (Pedroni 2004; Kao et al. 1999); this method accounts for heterogeneity in the model; *** and * show the level of significance at 1% and 10%, respectively

Dumitrescu and Hurlin panel causality

Dumitrescu and Hurlin (2012) panel causality estimation was used to further confirm the nexus among the variables. It will interest you to know that energy use and GDP per capita all signified feedback relationships with CO2 emissions, while a unidirectional link found running from real GDP and CO2 emissions. Similarly, CO2 radiation caused economic policy uncertainty; energy use; real GDP; and GDP per capita caused economic uncertainty, while feedback relationship is confirmed between real GDP and energy use.

Panel fully modified least squares (FMOLS) with weighted estimation

For robustness, as reported in Table 7, we used robust panel econometric techniques to deal with the issues of heterogeneity in the estimation (Pedroni 2004; Kao et al. 1999). In particular, this methodology utilizes since quite a while ago run covariances from the cross-segment gauges and reweights the information to represent heterogeneity in the estimation. Given the importance of this methodology, we apply the Group-FMOLS technique to evaluate the since quite a while ago run patterns among the parameters. The results from the Group-FMOLS are shown in Table 8. The results of Group-FMOLS show that the increase in energy use and economic policy uncertainty leads to a rise in carbon emissions, while real GDP and GDP per capita help reduce the growth of CO2 emissions. In conclusion, our robust analysis is not different from the findings from the PMG-ARDL result.

Table 7

Result of FMOLS

Variables	Model 1	Model 2	Model 3
ENU	1.0380***	1.0327***	1.0196***
RGDP	−0.1842***		−0.9734***
EPU	−0.0126***	−0.0113***	−0.1880*
RGDP2		−0.2056***	1.0548***
EPU*ENU			0.0583

Table 8

Results of the Dumitrescu and Hurlin (2012) panel causality

Null hypothesis	W-Sat.	P-value	Causality flow
ENU ≠ > CO2	3.8054***	0.0011	ENU ↔ CO2
CO2 ≠ > ENU	3.5114**	0.0074
RGDP ≠ > CO2	4.1180***	0.0001	RGDP → CO2
CO2 ≠ > ENU	2.3282	0.7477
RGDP2 ≠ > CO2	3.9506***	0.0004	RGDP2 ↔ CO2
CO2 ≠ > RGDP2	2.8619*	0.1662
EPU ≠ > CO2	2.6813	0.3100	CO2 → EPU
CO2 ≠ > EPU	2.6813***	0.0092
RGDP2 ≠ > ENU	3.8895***	0.0006	RGDP2 ↔ ENU
ENU ≠ > RGDP2	2.9321*	0.1274
EPU ≠ > ENU	2.3359	0.7415	ENU → EPU
ENU ≠ > EPU	2.8444*	0.1805
EPU ≠ > RGDP	1.6005	0.2584	RGDP → EPU
RGDP ≠ > EPU	3.2182**	0.0374
EPU ≠ > RGDP2	1.6345	0.2879	RGDP2 → EPU
RGDP2 ≠ > EPU	3.1051**	0.0634

Notes: ***, **, and * show the rejection of the null hypothesis at 1%, 5%, and 10% significance levels, respectively

Conclusion and policy implications

There are a considerable number of studies on the determinants of environmental quality. However, previous studies have not taken into account the influence of economic policy uncertainties, especially in OECD countries. For these reasons, we use annual data for a panel of 22 OECD countries between 1985 and 2017 to test the impact of energy use and economic policy uncertainties while accounting for other macroeconomic indicators. We applied robust econometrics techniques such as PMG-ARDL and Dumitrescu and Hurlin panel causality.

Empirical results support the argument that in the long run, energy use and economic policy uncertainties further deteriorate the quality of the environment. In contrast, renewable energy improves the quality of the environment. Similarly, energy use, real GDP, and GDP per capita to environmental degradation within the region in the short run. We also found a causal relationship between real GDP and GDP per capita to CO2 emissions, energy use to real GDP, CO2 emissions, energy use, real GDP, GDP per capita to economic policy uncertainties.

Given our findings, we will understand that energy use, real GDP, GDP per capita square, and economic policy uncertainties posed problematic to the environment since it leads to an increase in the CO2 emissions. Therefore, it has become a point of priority for the policymakers and government administrators to trade with caution in implementing policies on improving the quality of the environment. In addition, our study revealed that renewable energy source enhances the quality of the environment. Hence, the government of the OECD countries should adopt the use of renewable energy sources in their activities as commercial or home use. The outcome of energy-induced and economic policy uncertainty to pollution emission calls for a paradigm shift to renewables such as photovoltaic energy, hydroenergy, and wind energy, and for a promotion of renewable energy sources of electricity, grants, and taxes—holiday should be granted to investors. More so, FDI inflows should be cautiously directed to the investment in the renewable source of electricity, which are reputed to be cleaner and ecosystem friendly. Thus, there is a need for more efficient, modern, and cleaner energy technologies in the energy portfolio as a prerequisite for a successful transition from fossil fuel consumption while achieving a decarbonized economy that is in line with sustainable development goals (SDGs 8 and 13). Furthermore, to sustain the current momentum in OECD for sustainability target, there is a need to tighten commitment on environmental treaties like Kyoto Protocol and the Paris Agreement.

In conclusion, our study has revealed new findings, but not without limitation. In this present study, we were constrained to expand our study beyond the OECD countries due to the lack of data. Therefore, we will encourage future studies to consider broadening the scope of the survey beyond the OCED countries.