1. Introduction

1.1. Background

By the 1980s, human societies had gradually begun to recognize the importance of climate issues. In 1988, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) jointly established the Intergovernmental Panel on Climate Change (IPCC), withtheaim of assessing the state of climate change and its impacts on human society. Since 1990, the IPCC has published six assessment reports. In 1992, the United Nations Conference on Environment and Development (UNCED) adopted the United Nations Framework Convention on Climate Change (UNFCCC), which introduced the principle of “common but differentiated responsibilities.” This treaty entered into force in 1994. Starting in 1995, the parties to the convention have convened the Conference of the Parties (COP) on an annual basis. In 1997, the Kyoto Protocol was adopted at the third COP session.

The United States has long played an important role in global climate governance. In the 1990s, the Clinton administration signed the Kyoto Protocol. However, upon taking office, the George W. Bush administration announced in 2001 that the United States would withdraw from the agreement. Over the more than two decades from the Bush administration to the Biden administration, U.S. climate policy has experienced notable shifts, exhibiting a recurring oscillation between active and passive approaches.

1.2. Literature review

At present, there is a substantial body of research on climate issues, which can largely be divided into two categories: theoretical explorations of climate-related challenges and climate security strategies adopted by specific countries or regions.

The first category includes theoretical explanations of climate issues, with particular emphasis on studies that integrate securitization theory. Albert examined the link between climate emergency strategies and the securitization of climate change [1]. Mendes et al. focused on the relationship between climate vulnerability and securitization [2]. Kameyama and Takamura explored the definitional distinctions between “climate crisis” and “climate emergency,” and also addressed the issue of regional imbalance in climate security research [3]. Rhinard and colleagues used Nordic countries as case studies to investigate whether climate change has already been securitized, and proposed two types of climate securitization: threat-oriented and risk-oriented [4].

The second category centers on the climate security strategies adopted by particular countries or regions. Li applied hegemonic maintenance theory to systematically analyze the evolution of U.S. climate security strategy since 2000 [5]. Regarding Europe, Warner and Boas examined failed attempts at climate securitization in the United Kingdom and the Netherlands, suggesting that such efforts often function as policy boomerangs and may produce counterproductive effects [6]. Beyond traditional Western powers, an increasing number of scholars have begun to examine the climate policies of other nations. For example, Yamada analyzed the impact of Japan’s climate security discourse on the business community [7]; Oramah and colleagues investigated Nigeria’s framing of climate securitization [8]; and Rasheed studied the role Small Island Developing States (SIDS) play in United Nations Security Council debates on climate security [9].

1.3. The theory of historical institutionalism

Institutionalism emphasizes institutions such as rules and organized practices [10]. In the 1980s, March and Olsen introduced the concept of new institutionalism. In their view, new institutionalism seeks to integrate the study of behavior with the study of institutions, acknowledging both social context and individual motivation, while also emphasizing the autonomy of political institutions. Society influences the state, and the state, in turn, can shape society. Political institutions are not only a response to social forces but also have the capacity to influence historical processes [11].

New institutionalism is typically divided into three main strands: historical institutionalism, rational choice institutionalism, and sociological institutionalism [12]. Rational choice institutionalism emphasizes the normative analysis of institutions; sociological institutionalism explores the cultural factors that underpin institutions; and historical institutionalism focuses on the historical context surrounding institutional change. According to Steinmo and others, historical institutionalism examines how political struggles are shaped by the institutional settings in which they take place [13].

The theoretical core of historical institutionalism lies in the concepts of path dependence and critical junctures. Path dependence refers to the inertia exhibited by institutions once they are established; institutions tend to continuously self-reinforce and stabilize over time, making institutional change increasingly costly [14]. Although institutions possess strong inertia, they may still be altered by powerful external forces during significant historical moments. It is in this context that critical junctures arise, as major institutional transformations often occur in their aftermath. Over the course of historical development, path dependence and critical junctures often alternate with one another [15].

Institutional change can be divided into two stages: normal periods and critical junctures. During normal periods, institutional change follows the trajectory of path dependence, while critical junctures produce institutional ruptures that lead to the formation of new institutions [16]. Therefore, critical junctures function both as points of institutional break and as the starting points for a new path-dependent process. The punctuated equilibrium theory holds that institutional adjustment proceeds through three stages: stability, change, and renewed stability. Although critical junctures drive institutional rupture, newly established institutions often remain influenced by their predecessors, preserving certain core features [17].

Overall, historical institutionalism has been widely applied in studies of European integration, offering a new perspective for understanding the integration process [18]. In the case of U.S. climate policy, most existing research remains within the realm of policy analysis, and relatively few studies have employed historical institutionalism to explain its development. This paper seeks to apply historical institutionalism—particularly the concepts of path dependence and critical junctures—to examine the development and evolution of U.S. climate policy.

2. The shifts in U.S. climate policy: from George W. Bush to Joe Biden

2.1. Climate policy during the Bush administration

After Republican George W. Bush assumed the U.S. presidency in January 2001, U.S. climate policy encountered its first critical juncture. He reversed the Clinton administration’s previously active stance on climate issues and, in March 2001, announced the United States’ withdrawal from the Kyoto Protocol.

The Kyoto Protocol, adopted in 1997, is a supplementary agreement to the United Nations Framework Convention on Climate Change (UNFCCC). Based on the principle of “common but differentiated responsibilities,” the Protocol required developed countries to reduce their greenhouse gas emissions by an average of 5% below 1990 levels during the first commitment period (2008-2012). It also established three mechanisms for emission reduction: Emissions Trading (ET), Joint Implementation (JI), and the Clean Development Mechanism (CDM). As the world’s first legally binding agreement on greenhouse gas reductions, it represented a significant milestone. However, because the Protocol did not impose substantive emissions reduction obligations on developing countries, it faced considerable opposition within the United States. Therefore, although the Clinton administration signed and supported the Kyoto Protocol, the U.S. Senate ultimately did not ratify the agreement.

After taking office, George W. Bush opposed mandatory emissions reductions and instead advocated for voluntary efforts to curb greenhouse gas emissions. In an open letter addressed to Senators Chuck Hagel and three others in March 2001, he stated that he opposed the Kyoto Protocol because it would damage the U.S. economy and was unfair to the United States, as it exempted developing countries such as China and India from emission reduction obligations [19]. In a speech delivered in June 2001, Bush acknowledged that the United States was the world’s largest emitter of anthropogenic greenhouse gases and that the country should take responsibility for reducing emissions. However, he described the Kyoto Protocol as unrealistic in many respects, arguing that its targets lacked a solid scientific foundation. He warned that implementing the Protocol would ultimately harm the U.S. economy by causing job losses and driving up prices [20].

A few months later, the 9/11 attacks shifted national priorities toward counterterrorism, further pushing climate issues to the sidelines. In 2005, Hurricane Katrina caused severe economic losses and significant casualties across the United States; however, this did not change the Bush administration’s opposition to the Kyoto Protocol. Nonetheless, the disaster prompted various sectors of American society to begin reassessing the seriousness of climate change.

Although George W. Bush opposed the Kyoto Protocol, he did not entirely dismiss the importance of climate issues. For example, he proposed reducing the greenhouse gas intensity of the U.S. economy by 18% by 2012. He also established the Cabinet Committee on Climate Change Science and Technology Integration, jointly overseen by the Secretary of Commerce and the Secretary of Energy, to provide policy recommendations to the president. In 2001 and 2002, the administration launched the Climate Change Research Initiative (CCRI) and the Climate Change Science Program (CCSP) to strengthen scientific research on climate change [21]. In addition, Bush promoted international cooperation on climate-related matters. For instance, in 2001, the United States signed the CONCAUSA Declaration with the governments of Central American countries, emphasizing joint scientific research on climate change, the monitoring and assessment of greenhouse gases, and improved capacity for climate adaptation [22]. However, these efforts mainly focused on assessment and understanding, with relatively few concrete policies or regulatory measures.

Although the federal government maintained a generally lukewarm attitude toward climate issues, institutions such as Congress and the Department of Defense gradually began to recognize the significance of climate change.

In 2003, Senators John McCain, Joseph Lieberman, and others proposed the Climate Stewardship Acts and subsequently introduced related supporting bills. The goal was to cap greenhouse gas emissions at 2000 levels by 2010 and to establish a system of emission allowances [23]. However, these efforts ultimately failed, and Congress was unable to pass substantive climate legislation during the Bush administration. That same year, the Department of Defense released a report on Abrupt Climate Change Scenarios and U.S. National Security, emphasizing the need for the United States to develop predictive climate models, establish vulnerability metrics, and enhance water resource management in response to potential abrupt climate shifts [24]. In 2007, the CNA Corporation also highlighted in a report that climate change poses a threat to U.S. national security, recommending that it be integrated into national defense and security strategies, along with the establishment of long-term targets for greenhouse gas emissions reductions [25].

The Bush administration adopted certain measures to strengthen research on climate issues; however, it generally maintained a skeptical stance toward climate change. This skepticism was a key factor contributing to the critical juncture that emerged after he took office. From Bush’s perspective, the science behind global warming was insufficiently established, and it remained unclear whether greenhouse gas emissions were primarily caused by human activity or natural processes. Furthermore, he opposed mandatory emissions reductions, arguing that agreements such as the Kyoto Protocol were harmful to U.S. national interests. Consequently, the Bush administration never implemented substantive policies to address climate change, and the decision to withdraw from the Kyoto Protocol had serious negative consequences for global climate governance.

From another perspective, although the critical juncture following George W. Bush’s accession to the presidency led the United States to depart from the Clinton administration’s climate policy, Bush did not entirely reject the need to address the climate crisis and still set corresponding climate goals. American society was becoming increasingly aware of the importance of climate issues. To some extent, this shift can be attributed to the active climate policies of the Clinton era, which had helped raise public awareness of climate change. As a result, domestic pressure continued to challenge Bush’s conservative position, reflecting the inertia embedded in the climate policy framework established during the Clinton administration.

2.2. Climate policy during the Obama administration

In November 2008, after winning the presidential election, Democratic candidate Barack Obama pledged to usher in a new chapter of U.S. leadership on climate change during his term in office [26]. In 2009, upon taking office as the 44th President of the United States, U.S. climate policy reached another critical juncture.

In contrast to George W. Bush, the Obama administration placed significant emphasis on climate issues and formulated a comprehensive climate strategy. It undertook a range of measures to combat climate change, including setting clear domestic emissions reduction targets and increasing investment in climate-related initiatives. On the international stage, it strengthened cooperation and played a key role in the signing of the historic Paris Agreement.

In October 2009, President Obama signed Executive Order 13514, emphasizing that reducing greenhouse gas emissions should be a priority for the federal government [27]. In November, during his visit to China, the United States and China issued a joint statement affirming that climate change is one of the greatest challenges of our time and calling for enhanced international cooperation to address it. The statement also stressed the importance of respecting developing countries’ priorities for economic and social development in the context of climate action. Furthermore, the two countries pledged to work together to support the success of the Copenhagen Conference (COP15), promoting emission reduction commitments by developed countries and appropriate mitigation actions by developing countries [28]. However, at the subsequent Copenhagen Conference, significant disagreements persisted between developing and developed countries over emissions responsibilities, and the final Copenhagen Accord remained a non-binding political agreement.

In 2015, the United States reached several significant milestones in both domestic and international climate policy. On the domestic front, in February, President Obama signed Executive Order 13693, which required the federal government to reduce its greenhouse gas emissions by 40% from 2008 levels within the next decade and to increase the share of renewable energy in federal electricity consumption to 30% [29]. In August, Obama and the U.S. Environmental Protection Agency (EPA) officially introduced the Clean Power Plan (CPP). This initiative marked the first time the United States had established strict national carbon emission standards for power plants, aiming to cut total carbon emissions from the U.S. power sector by 32% below 2005 levels by 2030. Since power plants are the primary source of carbon dioxide emissions in the country, the plan was expected to significantly advance domestic emissions reduction efforts [30].

At the international level, the United States played an active role in promoting the adoption of the historic Paris Agreement. In September 2015, Chinese President Xi Jinping made a visit to the United States. The subsequent U.S.-China joint statement emphasized that the Paris Agreement should reflect the principle of “common but differentiated responsibilities,” with particularly attention to countries’ differing national circumstances and appropriate expression of differentiation [31]. This joint statement not only further solidified the U.S.-China consensus on addressing climate change but also laid an important foundation for the signing of the Paris Agreement two months later.

In December 2015, the Paris Climate Change Conference (COP21), attended by 196 parties including the United States and China, resulted in the adoption of the historic Paris Agreement. Its central goal is to limit the global average temperature increase to well below 2°C above pre-industrial levels, while pursuing efforts to limit the increase to 1.5°C above pre-industrial levels. The Paris Agreement replaced the top-down, mandatory allocation model of the Kyoto Protocol with a bottom-up approach, under which countries submit Nationally Determined Contributions (NDCs). The Agreement also outlines two core objectives: mitigation and adaptation. Both developed and developing countries are required to formulate climate plans in line with their respective development conditions to meet emissions reduction goals and strengthen adaptive capacity, thereby reducing vulnerability to climate impacts. Additionally, the Agreement includes provisions on financial support, technology transfer, and transparency [32]. It officially entered into force in November 2016. The Agreement covers the vast majority of countries worldwide, notably including China and the United States, the world’s two largest economies and emitters, making it broadly representative. It is widely regarded as a landmark achievement of the Obama administration’s climate policy.

Compared with the Bush administration, the Obama administration’s rise to power marked another critical juncture in U.S. climate policy. Obama reversed the Bush-era’s lukewarm stance and actively promoted U.S. engagement in global climate governance. However, this shift was not simply a case of institutional rupture. Although the Bush administration maintained a cautious approach to climate issues, its efforts to strengthen climate science, along with legislation and reports issued by institutions such as Congress and the Department of Defense, helped raise environmental awareness within American society. These developments laid the groundwork for Obama’s active climate policies upon taking office.

Obama’s efforts to promote the Paris Agreement and strengthen U.S. international leadership on climate issues bear certain similarities to Clinton’s signing of the Kyoto Protocol and his administration’s push for active U.S. engagement in global climate governance, reflecting the policy inertia of the Clinton-era. The policy legacy of the Obama administration, including the Paris Agreement, also laid the foundation for the climate agenda of the subsequent Biden administration. From another perspective, the Bush administration’s passive climate policies likewise exhibited a form of inertia. The social forces shaped by Bush’s climate stance did not disappear entirely following the critical juncture of the Obama era; rather, they helped lay the groundwork for the subsequent regression of U.S. climate policy under the Trump administration.

2.3. Climate policy during the Trump administration

After Donald Trump assumed the U.S. presidency in January 2017, U.S. climate policy underwent a significant rollback compared to the Obama era, marking another critical juncture. This shift was closely tied to the conservative and populist ideologies embraced by Trump and his supporters, which emphasized “making America great again,” expressed skepticism toward climate science, rejected the scientific consensus on climate change, and argued that emission reduction efforts should not come at the expense of American jobs. Consequently, upon taking office, Trump began to scale back government support for climate research and reversed many of the climate policies enacted under the Obama administration.

Soon after taking office, Trump moved to cut funding for the U.S. Environmental Protection Agency (EPA) and repealed the Clean Power Plan. In March 2017, his administration proposed a roughly 31% reduction in the EPA’s budget and halted funding for climate-related initiatives, including the Clean Power Plan [33]. That same month, Trump signed Executive Order 13783, which revoked several Obama-era climate-related executive orders and called for a formal review of the Clean Power Plan [34]. In June 2019, the Clean Power Plan was officially repealed and replaced by the Affordable Clean Energy Rule [35].

While repealing the Clean Power Plan domestically, Trump also initiated the process of withdrawing the United States from the Paris Agreement. In June 2017, he officially announced the U.S. withdrawal from the Agreement. In his speech explaining the decision, Trump argued that the Paris Agreement imposed heavy financial and economic burdens on the United States. He claimed that continued participation would lead to major declines in production in key industries such as steel, coal, and natural gas, resulting in substantial economic losses. At the international level, he contended that the Paris Agreement imposed relatively fewer obligations on countries like China and India, making it unfair to the United States [36].

In August of the same year, the U.S. Department of State released a media note regarding the Paris Agreement, stating that the United States remained open to rejoining the Agreement, provided it included provisions favorable to American businesses, workers, and taxpayers. The statement also emphasized that the U.S. supports a balanced approach to climate policy—one that reduces emissions while promoting economic growth and ensuring energy security. The United States would continue to pursue greenhouse gas reductions through technological innovation and cooperate with other countries to help them adopt clean energy more efficiently. Furthermore, the U.S. would remain engaged in international climate negotiations, including COP23 [37].

In November 2019, U.S. Secretary of State Mike Pompeo issued a statement announcing that the United States had formally submitted its withdrawal notice from the Paris Agreement to the United Nations, with the withdrawal set to take effect one year later. The statement reiterated President Trump’s June 2017 remarks on leaving the Agreement, asserting that the Paris Agreement placed an unfair economic burden on American workers, businesses, and taxpayers. It emphasized that the United States would continue to pursue a more realistic and pragmatic approach to climate issues and would cooperate with international partners to enhance capacities for addressing climate change [38].

During Trump’s four-year tenure, U.S. climate policy underwent yet another critical juncture. After taking office, Trump repealed several key climate policies from the Obama era, including the repeal of the Clean Power Plan and the decision to withdraw from the Paris Agreement. Compared to the Obama administration, there was a marked decline in the number of climate-related statements and publications on the White House and State Department websites, reflecting Trump’s lack of prioritization of climate policy. However, the Trump administration did not entirely rule out the possibility of rejoining the Paris Agreement, provided it aligned with U.S. economic interests. At the same time, the administration did not completely abandon international climate cooperation, as the United States continued to participate in COP23 negotiations.

Trump held a skeptical view of climate issues, emphasizing that environmental concerns should not hinder economic development and arguing that international agreements such as the Paris Agreement were unfair to the United States. This viewpoint closely resembled that of fellow Republican George W. Bush, who also believed that the Kyoto Protocol posed a threat to the U.S. economy and was unfair on the international stage. Trump’s conservative stance on climate issues and prioritization of economic interests over environmental considerations clearly reflect the policy inertia rooted in the Bush administration’s approach to climate governance.

2.4. Climate policy during the Biden administration

In the 2020 presidential election, Democrat Joe Biden defeated Donald Trump and officially assumed office as the 46th President of the United States in January 2021, marking yet another critical juncture in U.S. climate policy. Having served as Vice President during the Obama administration, Biden had long emphasized the importance of addressing climate change. In an interview during the 2020 campaign, he stated that climate change is the most pressing issue facing humanity and the greatest threat to U.S. national security. Biden pledged that, if elected, he would lead the United States back into the Paris Agreement [39].

After taking office, Biden swiftly fulfilled his commitment. On his first day in office, January 20, he signed an executive order announcing the United States’ re-entry into the Paris Agreement. That same day, he appointed John Forbes Kerry, former Secretary of State under the Obama administration and a key figure in promoting the Paris Agreement, as the Special Presidential Envoy for Climate. Kerry thus became the first member of the National Security Council to focus solely on climate issues [40].

Biden made it clear that climate policy would be central to the national strategy. On January 27, 2021, the Biden administration issued the Executive Order on Tackling the Climate Crisis at Home and Abroad, which explicitly placed the climate crisis at the core of U.S. foreign policy and national security. It emphasized the need for a government-wide approach and promoted interagency coordination in addressing climate challenges [41]. On the same day, the White House established the Climate Policy Office, appointing Ali Zaidi—who had held several roles during the Obama administration—as Assistant to the President and White House Climate Advisor, responsible for overseeing the implementation of concrete climate policies [42]. On February 19, the United States officially rejoined the Paris Agreement. In a press statement issued that day, the State Department underscored that climate change and scientific research must not be underestimated, but instead elevated as central priorities in both domestic and foreign policy, with implications for national security, immigration, trade, and other strategic areas [43]. In April, at the Leaders Summit on Climate, Biden announced a new emissions reduction target: to cut U.S. greenhouse gas emissions by 50% to 52% below 2005 levels by 2030. Biden framed this target as a way to create jobs, promote environmental justice, and ensure U.S. leadership in clean energy innovation [44].

Through the efforts of the Biden administration, the U.S. Congress passed two landmark pieces of legislation: the Bipartisan Infrastructure Law (BIL) in November 2021 and the Inflation Reduction Act (IRA) in August 2022. These laws are expected to significantly boost investment in carbon reduction programs across the United States, support the green development of American manufacturing, reduce greenhouse gas emissions, and facilitate the country’s energy transition. Over the long term, these measures are also expected to help the United States meet the goals set forth in the Paris Agreement [45].

At the international level, the Biden administration has prioritized restoring U.S. leadership on climate issues and strengthening global cooperation. The 2022 National Security Strategy identifies climate change as one of the defining challenges of our time. The United States seeks to advance international climate cooperation through platforms such as the Leaders’ Summit on Climate and the Paris Agreement, and to forge agreements with partners like the European Union to accelerate decarbonization [46]. In December 2023, following the agreement reached at COP28, President Biden issued a statement reaffirming the administration’s commitment to climate action. He emphasized transforming the climate crisis into opportunities for job creation and improved quality of life, restoring U.S. global leadership on climate, and enhancing international cooperation in this domain [47]. In February 2024, the State Department released a fact sheet reviewing the two-year progress of the Indo-Pacific Strategy, highlighting U.S. climate cooperation with regional partners. Notable efforts include the establishment of Just Energy Transition Partnerships (JETPs) with Indonesia and Vietnam and enhanced collaboration with the Indian Ocean Rim Association (IORA) on climate adaptation. According to the fact sheet, these initiatives help strengthen partner countries’ capacity to respond to climate change [48].

Compared to the Trump administration, the Biden administration has taken an entirely opposite approach to climate issues, marking yet another critical juncture in U.S. climate policy. While Trump prioritized economic interest over environmental concerns, Biden has placed climate change at the center of the national agenda. Building on the legacy of the Obama administration, Biden has appointed key Obama-era figures, such as John Kerry and Ali Zaidi, to lead domestic and international climate efforts. He has also enacted legislation like the Inflation Reduction Act, rejoined the Paris Agreement, and emphasized the importance of global cooperation. These actions have positively influenced global climate governance and demonstrate the policy inertia rooted in the Obama era.

3. Theoretical logic behind the trajectory of U.S. climate policy

From the perspective of historical institutionalism, institutional change is shaped by two key dynamics: “path dependence” and “critical junctures.” Over the more than two decades from the Bush administration to the Biden administration, U.S. climate policy has exhibited features of both critical junctures and path dependence.

Since the inaugurations of Presidents Bush (2001), Obama (2009), Trump (2017), and Biden (2021), U.S. climate policy has undergone four critical junctures. Under the Republican administrations of Bush and Trump, skepticism toward the scientific foundations of global warming prevailed, and economic priorities were consistently placed above climate concerns. Both administrations chose to withdraw from key international agreements such as the Kyoto Protocol and the Paris Agreement, asserting that these accords imposed unfair obligations on the United States and posed risks to national economic development. In contrast, the Democratic administrations of Obama and Biden placed climate change at the center of the national strategy. Domestically, they advanced policies such as the Clean Power Plan and the Inflation Reduction Act; internationally, they re-engaged with global climate governance by rejoining the Paris Agreement. Over the past two decades, U.S. climate policy has exhibited a pattern of oscillation between these divergent ideological and strategic approaches.

At the same time, the emergence of a critical juncture does not entail a complete institutional rupture; U.S. climate policy continues to exhibit elements of policy inertia. During the Clinton administration, the pursuit of active engagement in international climate governance and the signing of the Kyoto Protocol— despite its failure to be ratified domestically—contributed to raising public awareness of climate issues within American society. This societal foundation helped facilitate the Obama administration’s active participation in global climate governance and its efforts to enhance U.S. leadership in this domain after 2009. Similarly, the Obama-era initiatives such as the formulation of the Clean Power Plan and the endorsement of the Paris Agreement created a policy legacy upon which the Biden administration built following its inauguration in 2021. Biden’s appointment of key Obama-era officials such as John Kerry and Ali Zaidi, his immediate move to rejoin the Paris Agreement, and his efforts to restore U.S. leadership in global climate governance all demonstrate the continuing influence of institutional path dependence originating from the Obama administration.

Similarly, under the influence of policy inertia from the Clinton and Obama administrations, both the Bush (2001) and Trump (2017) administrations, despite their skeptical stances on climate change, did not entirely dismiss the significance of the climate agenda. The Bush administration promoted scientific research on climate issues by initiating programs such as the Climate Change Science Program (CCSP). Likewise, the Trump administration did not completely rule out the possibility of rejoining the Paris Agreement and continued to participate in international climate negotiations, including COP23. These measures illustrate how prior policy legacies constrained subsequent administrations, reflecting the enduring impact of institutional path dependence established during the Clinton and Obama eras.

While the “active climate policies” pursued by Clinton, Obama, and Biden reflect one form of policy inertia, the “passive climate policies” under Bush and Trump also exhibit their own path dependence. Bush’s emphasis on economic priorities over climate concerns and his withdrawal from the Kyoto Protocol shaped societal attitudes and institutional preferences that persisted beyond the critical juncture marked by Obama’s inauguration in 2009. When Trump assumed office in 2017, his administration’s renewed focus on economic growth, significant cuts to climate-related budgets, and withdrawal from the Paris Agreement were not isolated decisions, but rather manifestations of the policy legacy inherited from the Bush era. Similarly, the policy inertia from the Trump administration did not vanish with the critical juncture of Biden’s inauguration in 2021. In 2025, Trump was re-elected as U.S. president. Upon taking office, the United States once again announced its withdrawal from the Paris Agreement and cut climate-related investments [49], reflecting the continued inertia of policies from Trump’s first term.

4. Conclusion

Overall, over the course of more than twenty years from the Bush administration to the Biden administration, U.S. climate policy has exhibited a clear pattern of oscillation and fluctuation. Following the inaugurations of Bush (2001), Obama (2009), Trump (2017), and Biden (2021), the country experienced four critical junctures in its climate policy. The root cause of these shifts is closely tied to partisan politics. Republicans Bush and Trump prioritized economic interests over climate concerns, arguing that international agreements such as the Kyoto Protocol and the Paris Agreement were detrimental to the U.S. economy. Conversely, Democrats Obama and Biden placed climate change at the heart of national strategy, increasing investment in climate initiatives and seeking to enhance U.S. leadership in global climate governance.

At the same time, the occurrence of a critical juncture does not signify a complete institutional rupture or a fundamental systemic transformation. Both “active climate policies” and “passive climate policies” exhibit inertia, and this inertia does not entirely disappear with the emergence of a critical juncture. This helps explain why U.S. climate policy during this period repeatedly oscillated between active and passive approaches. The passive climate policies of Bush and Trump were never able to persist indefinitely, nor were the active climate policies of Obama and Biden able to continue without interruption. Rather, policy shifts emerged at critical junctures brought about by changes in leadership. Importantly, these shifts did not constitute complete institutional breaks but were consistently shaped by the policy inertia of preceding administrations.

Looking across the historical trajectory of U.S. climate policy from the Bush to the Biden administrations, one can clearly observe the alternating interplay between the two logics of institutional change: “critical junctures” and “path dependence.” The political contest between Democratic and Republican leaders over climate issues not only reveals institutional ruptures brought about by critical junctures, but also underscores the underlying path dependence that persists beneath these breaks. To some extent, the evolution of U.S. climate policy over the past two decades offers fresh empirical cases and theoretical insights for the continued development of historical institutionalism.