**1. Introduction**

Carbon emissions are the result of the use of fossil fuels to generate the energy required for production. They lead to the greenhouse effect, causing radiation that would be returned to space to remain in the atmosphere. Increasing carbon emissions since the industrial revolution, together with other greenhouse gases such as methane (CH4), (HFCs), and sulfur hexafluoride (SF6), have been the main cause of hydrofluorocarbons climate change and environmental crises. Considering that climate change occurs with the interaction of three important parameters—economy, energy, and environment—the best way to prevent climate change and to minimize its negative effects is to reduce anthropogenic greenhouse gas emissions [1].

To mitigate the adverse impacts of greenhouse gas emissions, global initiatives have been undertaken by industrialized countries such as the Montreal Protocol, the United Nations Framework Convention on Climate Change (UNCC), the Kyoto Protocol, the European Union (EU) Green Deal, and the Paris Agreement. The Montreal Protocol, which required 196 countries to stop the production of substances that damage the ozone layer, is considered to have been the most successful multilateral agreement on the environment [2]. The Kyoto Protocol, signed within the framework of the UNCC, foresees developed countries reducing their gas emissions by 5% compared to levels in 1990, and to reduce their emission values for an average of five years [3]. The Paris Agreement is the only globally legally binding monitoring agreement and, unlike the Kyoto Protocol, it lays a burden

**Citation:** Çolak, O.; Özuyar, S.E.G.; Bölükba¸sı, Ö.F. Asymmetric Effects of the Defense Burden on Environmental Degradation: Evidence from NATO Countries. *Sustainability* **2023**, *15*, 573. https:// doi.org/10.3390/su15010573

Academic Editors: Akrum Helfaya and Ahmed Aboud

Received: 18 November 2022 Revised: 16 December 2022 Accepted: 25 December 2022 Published: 29 December 2022

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

for not only developed countries, but the rest of the world as well. The effect of the Paris Agreement was immediately apparent in Europe. It stipulates conserving the universal mean temperature to 2 ◦C above pre-industrial standards to restrain climate change [4]. With the EU Green Deal, EU countries aim to reduce carbon emissions by 55% by 2030 and to transform the European economy in order to become a "carbon-free continent" by 2050 [5]. Similarly, China is seeking to reach its highest carbon emission by 2030 and to achieve carbon neutrality by 2060 [6]. As calculated by the Intergovernmental Panel on Climate Change, 76% of the gases causing climate change are CO2, 16% are methane and 6.2% are nitrous oxide gases; therefore, respectively [7]. Therefore, as an essential element of greenhouse effect, analyzing the effects of the defense burden and energy use on CO2 emissions would contribute to the literature on climate change.

The effects of climate change and the desire to leave a more livable world to future generations have led to the idea that countries cannot exist only with economic growth, but also must be involved in a multi-faceted transformation process [8]. Calculations that global material use will increase from 89 gigatons to 167 gigatons between 2017 and 2060 and that gas emissions causing global warming will increase accordingly have caused a change in perspectives on the concept of sustainability. Brutland's motto of "producing more with less" has evolved into a different growth concept with the internalization of externalities; in this way, responsibility is placed on countries that growth in use of resources and production be realized without harming the environment. Thus, having first been introduced in 1987 in the report of the World Commission on Environment and Development titled "Our Common Future", sustainability has been defined by the Global Sustainability Development Report (2019) and become a more grounded concept [9].

To achieve development objectives, countries aim to achieve greater industrialization. With the unprecedented pace of industrialization in recent decades, pressures on natural resources have emerged that are being widely discussed by environmental scientists and policy makers. In order to control natural resources, countries tend to spend on their military operations. Those military operations bear potential risks to the environment due to their excessive depletion of natural resources. Furthermore, those environmental risks do not necessarily emerge in warfare. For instance, construction of military bases might occur at the expense of the destruction of forest areas, gasoline consumption may result in air pollution due to the deployment of military personnel by vehicles, and ammunition and personnel waste are associated with environmental pollution. These are some potential cases of militarization resulting in environment degradation. According to the Stockholm International Peace and Research Institute (SIPRI), worldwide military expenditures have reached their greatest historical level and accounted for 2.4% of the world's GDP in 2020. The top fifteen military spenders accounted for 81% of global military spending, at USD 1603 billion, in 2020. The leading country in military spending is the United States of America (USA) at USD 778 billion, followed by China, India, the Russian Federation, and the United Kingdom (UK) [10].

In 1949, after World War II, the North Atlantic Treaty Organization (NATO) was established to ensure the territorial integrity of member states and solve political and military disputes between them. In addition to its general mission regarding the security issues of member states, NATO has also taken various actions to address sustainability issues since the end of 1960s. In this respect, the earliest attempt was the 1969 establishment of the Committee on the Challenges of Modern Society (CCMS), which was designed to initiate and support studies and fellowships to deal with all forms of pollution and disposal of hazardous wastes. Nonetheless, essential actions have been accelerated by the turn of the new millennium, with the rapidly growing interest in climate change and environmental concerns, as demonstrated by UN initiatives. In 2006, CCMS evolved as the Science for Peace and Security Plan to execute initiatives dealing with environmental security challenges. Among the most notable initiatives was the introduction of the Smart Energy Initiative, which calls for energy efficiency and innovative technologies to maintain the operations of the alliance. In addition, the concept of "Green Defense Framework" was ratified by the member states at the Wales Summit in 2014 [11]. In 2021, militarization and the environmental crisis were an "important issue" within the framework of the Climate Change and Security Action Plan [12]. In addition, this situation is also considered in Brussels Submit of NATO in 2021. In the final declaration of the Submit, heads of states and governments committed to reduce greenhouse emissions to zero by 2050 [13]. However, the current position of NATO regarding environmental issues is mainly built upon awareness, information sharing, education and training activities of troops, and helping member states in the light of their own regulations and measures.

On the other hand, studies of defense economics have mainly addressed the macroeconomic effects of militarization, either theoretically or empirically, despite the presence of recent growing interest in environmental concerns. This article aims to empirically analyze the relationship between militarization and environmental degradation in terms of the treadmill of destruction theory, both symmetrically and asymmetrically, for the 15 oldest NATO countries over the period 1965–2018. The treadmill of destruction theory suggests that countries with more labor-intensive and cutting-edge technologies demand more natural resources. There are two basic motivations worth highlighting for this study. The first motivation is directly related to the purpose of this study. This paper aims to fill gaps in the literature in various aspects. First of all, it is a preliminary attempt to empirically address the asymmetric effects of militarization on environmental degradation, giving special focus to NATO. In other words, it differs from all studies in the literature, as it deals with the relationship between defense expenditures and the environmental degradation for NATO member countries from an asymmetrical point of view, which allows the observation of both sudden changes in military expenditures on environmental degradation and asymmetric long-term cointegration. In fact, NATO deserves special attention, since it accounted for 55% of global military expenditure in 2020 [10]. It should also be noted that six countries (the list of the countries by expenditure level is as follows: United States of America (USA), United Kingdom (UK), Germany, France, Italy, and Canada) of the top fifteen military spenders are members of NATO. Furthermore, four member states of NATO (the USA, Germany, Canada, and Turkey) were among the top fifteen CO2-emitting countries in the world in 2020 [14]. Since NATO, which has focused on many security issues since the Cold War period, has recently focused on environmental degradation as creating a possible global security problem, this study, as among a few militarization and environmental studies, focuses on the subject in regard to NATO. In addition, our empirical investigation is limited to fifteen member states of NATO. Most of the countries in the sample are regarded as the founders of the alliance. Accordingly, these 15 countries are the top military spenders and top carbon emitters. Although NATO is an alliance between the member states, some members have engaged in arms races with each other. Greece and Turkey are members that have a significant defense burden due to historical and ongoing geopolitical conflicts with each other.

The second motivation for this paper lies on the methodology used throughout, which is relatively a novel approach and thought to fill a gap in the empirical literature. Except for Ullah et al. [15], the majority of empirical studies have examined the effect of militarization on environmental degradation in a linear context. Our study aims to detect asymmetric effects for a relatively broader group of countries that are considered as contenders in terms of arms races and are top emitters globally. To the best of our knowledge, this goal has not been specifically addressed in the empirical literature thus far. This study also aims to contribute a new dimension to the literature by integrating the effects of changes in the defense burden into a long-term relationship within the scope of the treadmill of destruction theory. Within the context of time-series analysis, an autoregressive distributed lag (ARDL) approach to cointegration presents some advantages. First of all, ARDL generates efficient results with small sample sizes. Secondly, the variables can be integrated by different orders. Finally, the inclusion of an error correction model integrates short-term dynamics into the long-term equilibrium model [16]. In addition to these advantages, NARDL methodology allows for examining the asymmetric interplay by decoupling the variables into positive

and negative components when generating the effects of changes. The selection of the sample period is mainly dictated by the availability of data on carbon dioxide emissions and primary energy use, which were gathered from British Petroleum's (BP) Statistical Review Database. It should also be noted that the sample period was selected to be long as possible in order to efficiently analyze the time-series characteristics of the data with respect to the availability of data for those countries.

In line with the aforementioned arguments, the layout of the present paper is as follows. The Section 2 presents the theoretical arguments on the nexus of militarization and the environment. The Section 3 is devoted to a literature review, in which we present theoretical and empirical studies, giving special focus to militarization and the environment. In the Section 4, we present our model and empirical strategies, and discuss the data issues. In accordance with the modeling and our empirical strategy, we present the findings of our estimations in the Section 5. Finally, in the Section 7, we terminate our paper with concluding remarks and policy recommendations.
