Political Polarization and Climate Policy Implementation: An Analysis Based on Panel Data of Carbon Dioxide Emissions in U.S. States

1. Introduction

Climate change represents a significant international issue that impacts the survival of all humanity. On June 3, 1992, the United Nations Conference on Environment and Development passed the United Nations Framework Convention on Climate Change, leading to a series of international cooperations centered around environmental issues. In the governance of global climate, developed countries, with the United States at the forefront, play an indispensable role. First, these nations are responsible for a larger volume of greenhouse gas emissions and thus bear a greater responsibility in addressing climate change. Second, developed countries can leverage their power and influence to encourage other nations to participate in collective action aimed at achieving environmental protection goals (Keohane, 1984). Consequently, the actions of developed regions and countries like the United States and Europe, in terms of financial support for climate change adaptation, the transfer of green technologies, and the commitment to quantifiable emission reductions, significantly determine the effectiveness of global climate governance.

However, the United States’ performance in global climate governance is often hampered by its domestic politics. In recent years, polarization between the two major parties and the changing of governing parties have significantly influenced the United States’ stance on global climate governance. During his tenure, Democratic President Barack Obama frequently emphasized the scientific facts of climate change and implemented a series of environmental policies based on these facts. Republican leader Donald Trump, on the other hand, led the United States to withdraw from the Paris Agreement, often expressing skepticism and denial of climate change, which greatly weakened the United States’ leadership in climate governance. Since 2020, with Democratic President Joe Biden’s inauguration and the establishment’s return, the United States has once again placed climate change at the center of its foreign and national security policies (Zhou and Zhuang, 2021). Biden repeatedly emphasized the importance of climate issues during his campaign and promised to lead the United States back to the international stage of climate governance. This illustrates that the tradition of party politics and the phenomenon of political polarization in the United States have a clear impact on the formulation of its climate policies.

Climate policy represents a significant area of divergence between the two major parties in the United States. Under the American political system, the governing party’s will shapes the United States’ involvement in global climate governance, while state policies vary according to the local political environment and the governor’s party affiliation. At the federal level, the stance of the governing party largely dictates the direction of climate policy. At the state level, the party background and personal preferences of governors play a key role in policy formulation and implementation. In light of this, this paper will analyze the relationship between the party affiliation of governors across the United States and the carbon dioxide emissions of their respective states using quantitative methods. This empirical examination aims to investigate the relationship between party politics and climate governance in the United States, and, based on these findings, explore the inefficiencies in governmental governance against the backdrop of political polarization.

2. Literature Review

2.1. American bipartisanship and political polarization

The development of party politics in the United States can be traced back to the late 18th century with the Federalist Party and the Democratic-Republican Party. These parties represented the major political divisions in early American politics, including differing views on the power of the federal government and how to manage relations with Europe. In 1828, Andrew Jackson’s victory in the presidential election marked the beginning of the Second Party System, with Jackson and his followers subsequently forming the new Democratic Party (Lipset, 1981). In 1854, due to disagreements over slavery, the Republican Party was established among anti-slavery activists in the North. This new party successfully elected Abraham Lincoln as president in 1860 (Gienapp, 1987).

Since the establishment of the Democratic and Republican parties, U.S. party politics have largely revolved around these two parties. Political polarization refers to the ideological extremization of political parties, and in recent years, the polarization between the two major parties in the U.S. has evolved into a comprehensive socio-political polarization (Zhou and Mu, 2022). This is primarily manifested in the extreme opposition between the two parties on issues such as culture, ethnicity, and social welfare (Layman and Carsey, 2002). The literature on U.S. political polarization primarily focuses on the causes, current state, and impact of this phenomenon. The causes include the economic shocks of globalization, the shrinking middle class, the rise of populism and far-right forces, intensifying racial conflicts, the push from social media, highly differentiated social interests, and issues stemming from these, such as homosexuality and gun violence (Diao, 2017; Zhou, 2017). Moreover, the intensification of U.S. political polarization is closely linked to its constitutional system and the presidential primary system, with the political elite’s pursuit of personal influence and party interests also contributing to political polarization (Diao, 2016; Jin and Tang, 2019). Currently, as the polarization between the two parties deepens, the Democratic and Republican parties have engaged in malicious competition in recent elections, prioritizing party interests over national interests. This has led to executive–legislative conflicts, congressional divisions, and violent conflicts during the transition of power (Zhou, 2017). Furthermore, the party identification and emotional polarization of U.S. voters have been strengthening against the backdrop of political polarization (Mu, 2022).

From the perspective of impact, political polarization has plunged U.S. politics into the dilemma of “vetocracy”. Francis Fukuyama, in describing vetocracy, mentioned that “all institutional rules that delegate power to different political actors within the system constitute potential veto points, where individual vetoers can stop the entire system’s action. Almost all features of the U.S. Constitution — presidentialism, bicameralism, federalism, and judicial review — though functionally different, can be seen as potential veto points in the process of making collective decisions (Fukuyama, 2014)”. For example, within the U.S. Congress, the Republican and Democratic parties often go to great lengths to block the proposals of the opposing party under the backdrop of political polarization. Political polarization and vetocracy have led to low legislative efficiency in Congress, inefficient government governance, a lack of continuity in public support, and difficulties in democratic negotiation (Zhou and Mu, 2022).

2.2. U.S. political polarization and climate policy

Climate change is a significant international issue threatening the survival of all humanity, and as one of the major greenhouse gas emitters, the United States’ policies on climate change have a substantial impact on international climate governance. However, compared to other developed countries, the United States has maintained a passive stance in international climate negotiations. Regarding the political polarization in the United States and its climate policy, academia has mainly focused on the driving factors and obstacles to U.S. climate policy.

From the perspective of the drivers of climate policy development, the issue of climate has a weak political foundation in the United States. The government often emphasizes the significance of climate policy for America’s energy security and economic development, with less attention to climate change itself (Xie, 2020). In the U.S. political environment, the primary goal of political parties is to win elections, so Democratic presidents often emphasize climate issues to serve their electoral politics needs and achieve internal unity within the Democratic Party (Li and Qi, 2021; Mu, 2022). Internationally, the United States faces pressure from the European Union and developing countries due to its passive stance on climate governance issues. At the same time, the U.S. aims to enhance its diplomatic influence through climate issues, all of which affect the development of U.S. climate policy (Yu and Li, 2013). Additionally, the personal attitude of the president toward climate change significantly influences the direction of U.S. climate policy (Li and Song, 2017).

Regarding the impediments, the negative performance of the United States in climate policy is mainly influenced by political polarization, economic deterioration, and declining power. Political polarization affects U.S. climate policy at both the congressional and state government levels, with climate policies proposed by Democratic presidents often facing opposition from Republican lawmakers at the congressional level, and Republican governors resisting federal environmental policies at the state level (Yang, 2016). The implementation of climate policies entails high economic and social costs, leading Republican presidents to pursue policies unfavorable to environmental protection, often for economic reasons (Kong and Li, 2018; Xu, 2013). The recent negative performance of the United States in international climate governance is primarily due to its relative decline in power and a decreased willingness to provide international public goods (Liu, 2012).

Current research on U.S. climate governance is mostly theoretical, with a lack of empirical studies on the impact of political polarization on climate governance. Employing quantitative methods to delve into this issue will help us better understand the complex relationship between party politics, political polarization, and climate issues.

3. Climate Policy in the Context of Political Polarization in the United States

3.1. Bipartisan dynamics in the evolution of U.S. climate policy

The evolution of American bipartisan recognition of climate issues has undergone a lengthy development process. In the early 20th century, both parties paid significant attention to climate and environmental issues. Republican President Theodore Roosevelt, since taking office in 1901, established numerous national forests, nature reserves, and parks (U.S. National Park Service, 2017). Democratic President Franklin D. Roosevelt founded the Civilian Conservation Corps and advanced many decrees and legislations aimed at protecting the environment, laying a solid foundation for future environmental efforts (U.S. National Park Service, 2017). In the 1970s, under the push of Republican President Nixon, the U.S. Congress passed many important environmental acts and established the Environmental Protection Agency (US EPA, n.d.).

In the 1980s, as the industrialization process rapidly advanced, the consensus on environmental protection was undermined. Republican President Ronald Reagan cut the environmental budget and slowed down environmental enforcement (Shabecoff, 1989). Subsequently, Republican President George W. Bush further relaxed environmental regulations, promoted the decentralization of environmental laws, and decelerated the implementation of environmental policies. In 1994, Republican Newt Gingrich became the Speaker of the House, actively advancing legislative reforms and attempting to reduce the size of the federal government, measures that severely impacted the environmental cause in the United States (Sellers, 2018).

3.2. The climate policy struggle between U.S. political parties

In recent years, the two parties have progressively moved toward comprehensive confrontation, with escalating political polarization exacerbating the divergence over climate issues (Zhou and Mu, 2022). The Democratic Party has consistently supported environmental issues and actively engaged in and promoted the process of global climate governance; in contrast, the Republican Party has focused more on economic development and maintained a reserved stance toward climate agreements.

On one hand, the division between the two parties on climate issues has influenced policy at the federal level in the United States. Democratic President Obama implemented a series of energy innovation and climate change policies during his tenure and actively participated in international climate governance (Yu and Li, 2013). Republican President Trump, upon taking office, completely overturned Obama’s climate policies and withdrew from the Paris Agreement, severely damaging the global climate cooperation process (United States Department of State, 2019). After Democratic President Biden took office, the U.S. once again prioritized climate issues on its agenda and actively sought a leadership role in global climate action after rejoining the Paris Agreement (Zheng and Yang, 2021). Overall, the divergences in climate policy between the two major U.S. political parties not only reflect the trend of domestic political polarization but also have a profound impact on the process of global climate governance.

On the other hand, the differences between the two parties have had a significant impact on state-level climate policies. In the American political system, states have considerable autonomy in implementing environmental policies. Although the federal government can provide uniform policy guidance, state governments can develop and implement different climate policies based on local conditions (Center for Climate and Energy Solutions, n.d.). Compared to the federal government, state governments have greater autonomy and a smaller management scope, making it easier for state policies to be unified. Therefore, U.S. state-level policy-making and implementation on climate issues are more susceptible to political polarization. For example, Democratic governors often adopt proactive policies to address climate change. Following Trump’s announcement of withdrawal from the Paris Agreement, Democratic governors of New York and California quickly responded by forming the “United States Climate Alliance” to ensure their emission reduction commitments under the Agreement were implemented. The Governor of California also established official cooperation with the Chinese government on climate issues and founded the California-China Climate Institute (Farber, 2021). Within the Republican Party, there are many climate skeptics, such as Obama’s Clean Power Plan, which was obstructed by Republican governors and could not be implemented properly in Oklahoma (Oklahoma Secretary of Energy & Environment, n.d.). Former Florida Governor Jeb Bush has publicly expressed skepticism about climate change (Wu, 2016), and Nevada Governor Brian Sandoval directly vetoed environmental legislation that had been passed by the state legislature (Shogren, 2017). Therefore, this study will focus on the policies of U.S. states, which are more evidently affected, proposing the following two hypotheses:

	Hypothesis 1. The effectiveness of climate policy implementation in U.S. states is influenced by the partisan affiliation of the state’s governor.
	Hypothesis 2. Democratic governors will have a positive impact on the implementation of climate policy in their states, while Republican governors will have a negative impact.

In the metric setting, this study selects carbon dioxide emissions as the fundamental indicator for assessing the climate policy level of the two parties. In the 1950s, American scientist Charles David Keeling selected Mauna Loa in Hawaii as the location for monitoring carbon dioxide concentrations. Based on the data from the Mauna Loa Observatory, researchers developed the “Keeling Curve”, which shows that the concentration of carbon in the atmosphere has been gradually increasing over the past decades. As a piece of scientific evidence, the Keeling Curve indicates that human activities are altering the Earth’s climate (Dennis, 2022). This finding has proven that carbon dioxide emissions have become an important standard for the international community to measure the extent of human impact on climate change, and the academic community often uses CO₂ emissions as the dependent variable to examine the effectiveness of climate or energy policies (Baiardi, 2020; Zheng et al., 2023). This paper uses the carbon dioxide emissions of U.S. states as the indicator to measure the effectiveness of their climate policy implementation. It analyzes the relationship between the governor’s party affiliation and the state’s carbon dioxide emissions through the method of panel data modeling, thus providing a more intuitive understanding of how political polarization affects the implementation effectiveness of domestic climate policy in the United States.

4. Research Design

4.1. Data source and variable description

Considering the critical role of governors in state climate policies in the context of political polarization in the United States, this paper selects balanced panel data for 50 states from 1997 to 2020 to empirically analyze the effects of climate governance under Democratic and Republican governors. The variables are explained as follows:

Explained variable: carbon dioxide emissions. Using carbon dioxide emissions from 1997 to 2020 in selected 50 states as the explained variable, this paper examines the effect of the governor’s party affiliation on the state’s climate governance effectiveness. The carbon dioxide emissions data used in this paper come from the Energy Information Administration (EIA), the statistical agency of the U.S. Department of Energy.

Core explanatory variable: governor’s party affiliation. To ensure the accuracy of the data, the classification of state party affiliation in this paper will be strictly based on the governor’s party affiliation each year. Two dummy variables are set up, respectively, “Dem” and “Rep”, which represent the Democratic and Republican governors. During the study period from 1997 to 2020, if a state has a Republican governor in office in a given year, the Dem is 0 and the Rep is 1; if the governor is a Democrat, the Dem is 1 and the Rep is 0. If the government is governed by an independent, both Dem and Rep are 0.

Control variables: four control variables are selected in this paper to eliminate confounding factors that may affect the relationship between the explained variable and the explanatory variable, to improve the accuracy of the estimation results. The four control variables in this paper are population, gross domestic product (GDP), energy consumption per unit of GDP, and coal consumption. First of all, there is bound to be a link between the size of a place’s population and its carbon dioxide emissions (Martínez-Zarzoso et al., 2007). Therefore, this paper selects the annual population numbers of the 50 states between 1997 and 2020, using data from the US Bureau of Economic Analysis and the US Census Bureau. Second, the link between GDP and carbon dioxide emissions has also been confirmed by the academic community (Friedl and Getzner, 2003). Therefore, this paper selects the annual GDP information of 50 states, which also comes from the US Bureau of Economic Analysis. Third, energy consumption per unit of real GDP is a measure of how efficiently an economy uses energy to produce each unit of GDP, which is the ratio of energy consumption in the United States to adjusted real GDP (U.S. Energy Information Administration, n.d.). These data represent the total energy use required to support economic and social activities, and can be used to represent the energy efficiency of an economy, and the role of energy efficiency in reducing carbon dioxide emissions has been proven (Tajudeen et al., 2018; United Nations Division for Sustainable Development, n.d.). Therefore, this paper selects energy consumption per unit of real GDP for each of the 50 states over the years, based on data from the U.S. Energy Information Administration. Finally, there is a correlation between coal consumption and carbon dioxide emissions (Bloch et al., 2012). Therefore, this paper collected year-to-year coal consumption for all 50 states, again from the U.S. Energy Information Administration. To sum up, the basic statistical characteristics of the variables selected in this paper are shown in Table 1.

4.2. Model construction

This paper constructs a panel data model to analyze the relationship between the governor’s party affiliation and carbon dioxide emissions. The model is set as follows :

where the explained variable ${\mathrm{\text{CO}}}_{2it}$ represents the carbon dioxide emissions of the i state in year t; The core explanatory variables ${\mathrm{\text{rep}}}_{it}$ and ${\mathrm{\text{dem}}}_{it}$ indicate the party affiliation of the governor of the i state in year t. ${\mathrm{\text{pop}}}_{it}$, ${\mathrm{\text{gdp}}}_{it}$, ${\mathrm{\text{ene}}}_{it}$, and ${\mathrm{\text{coal}}}_{it}$ represent four control variables representing the population, GDP, energy consumption per unit of real GDP, and coal consumption of the i state in year t, respectively. ${\mu }_i$ stands for individual fixed effects, representing some of the characteristics of each state, such as geographical location, culture, and resource endowments. ${\tau }_t$ stands for time-fixed effects, which represent factors common to all states that change over time, such as national economic policies, global trends in climate change, and so on. ${\epsilon }_{it}$ represents the random error term.

5. Analysis of Empirical Results

5.1. Descriptive statistics

As can be seen from Table 1, the average carbon dioxide emissions of the states are 112.20, the maximum is 684.7, and the minimum is 5.42. It shows that there are great differences in carbon dioxide emissions in states, which are caused by different economic development degrees, population gaps, and other factors.

5.2. Correlation coefficient matrix

Before the regression analysis, it is necessary to test the Pearson correlation coefficient matrix on the data. The correlation coefficient matrix among all indicators is shown in Table 2.

As can be seen from Table 2, there is a certain correlation between the core explanatory variable, namely the governor’s party affiliation, and the explanatory variable’s carbon dioxide emissions, indicating that the governor’s party affiliation will have a certain impact on the state’s carbon dioxide emissions. This conclusion is in line with the expected hypothesis of this paper. However, this conclusion does not exclude the interference caused by the control variables and error terms, so further regression analysis is needed.

5.3. Hausmann test

Common models for panel data include the mixed-effect model, fixed-effect model, and random-effect model, and the Hausmann test can determine which model the data in this paper are suitable for. The results of the Hausmann test in this paper are shown in Table 3.

According to Table 3, the Hausmann test statistic is 42.13, with a p-value of 0.00, which is less than 0.05. This result indicates that the null hypothesis should be rejected, and therefore, a fixed effects model should be chosen.

5.4. Regression results of fixed-effect model

To further analyze the influence of the party affiliation of governors in different regions of the United States on carbon dioxide emissions, this paper divides the 50 states into four regions, Northeast, Midwest, South, and West, according to the practice of the United States Census Bureau (U.S. Census Bureau, n.d.). The total sample and the regression results of the four regions are shown in Table 4.

5.5. Analysis of data results

From the data in Table 4, the following conclusions can be drawn. First, there are differences between the parties’ positions on climate policy. In the total sample, the Northeast, the South, and the West, there are significant differences between Democratic and Republican governors. This reveals the partisan divide on climate change and how it manifests itself in policy decisions and implementation at the state level. This difference means that when the power centers of states are in different political parties, there will be significant differences in carbon emissions policies between regions. Therefore, the partisan nature of governors has a de facto effect on the implementation of state climate policies. Still, the direction of this effect is not fixed with the Democratic or Republican Party, which supports Hypothesis 1 and rejects Hypothesis 2.

Second, the U.S. political system is flawed by unfulfilled electoral promises. At the national level and in the Northeast and South of the United States, Democratic governors have a significant positive effect on carbon dioxide emissions, a conclusion that seems to contradict the previous claim that Democrats support environmental protection. In the political system of the United States, winning elections is the primary objective of political parties. Consequently, all actions undertaken by these parties are aimed at garnering the maximum number of votes. Moreover, the policies proposed by political parties during election periods are designed to serve the purpose of securing electoral victory (Downs, 1957). In the context of political polarization, candidates who display radical attitudes on specific issues tend to gain the favor of voters. Some Democratic governors may make promises on environmental protection and the promotion of new energy during the election period, but after taking office, they may be forced to shelve environmental issues under realistic pressures such as economic development and employment issues, which eventually lead to higher greenhouse gas emissions. This reflects the fatal flaw in American democracy, in which the parties, competing for votes, can focus too much on superficial policy promises and lose sight of the real needs of the public and the long-term interests of the country.

Third, the lack of policy continuity is caused by the two parties’ alternate governance. To effectively address climate change, policy continuity and stability are essential. However, the results of the data show that there are significant differences in the corresponding carbon emissions when different parties are in power. This indicates that the environmental protection work of a state may change dramatically when the political party changes, thus affecting the coherence and implementation effect of climate policies, and such policy discontinuity may impair the effectiveness of climate governance in the United States. The capricious climate policies brought about by the change of political parties in the United States have greatly damaged the credibility and image of the United States in global climate governance, from the Clinton administration’s support for the Kyoto Protocol to the George W. Bush administration’s refusal to ratify the Kyoto Protocol; from the Obama administration’s push to sign the Agreement to the Trump administration’s withdrawal from the Agreement, the irresponsible behavior of the United States on this issue has been widely questioned by the international community (Li and Qi, 2021).

In addition, the four control variables in this paper, namely population, GDP, energy consumption per unit of real GDP, and coal consumption, also affect the carbon dioxide emissions of the states in different degrees and directions. The positive correlation between coal consumption and carbon dioxide emissions suggests that coal use remains a significant factor in carbon dioxide emissions across U.S. states. It can be seen that in the context of party politics and political polarization, parties may have different positions and policies on coal use and coal alternative energy policies, which may affect coal consumption in states and further affect carbon dioxide emissions.

6. Conclusion

Climate governance policy is one of the major areas of disagreement between the two parties in the United States. This paper provides an empirical analysis of carbon dioxide emissions from the 50 states of the United States from 1997 to 2020. It explores the climate policies of the two major political parties, the Democrats and the Republicans, and their effects. The results of this analysis show that within the United States, climate policies and their effects tend to vary significantly across states depending on the party affiliation of the governor. In the accepted acknowledgement, Democrats are seen as environmental advocates, while Republicans are seen as relatively negative. However, the results of this paper show that under certain circumstances, states with Democratic governors have higher carbon dioxide emissions than states with Republican governors. Some governors have not fully fulfilled their election promises, which also shows that the two parties in the United States ignore the long-term national interest for partisan interests in the election, and this problem is particularly obvious on the issue of climate change.

The difference between the two parties on climate issues reflects deeper social contradictions and rifts in the United States. Economic development and climate policy are hot topics in the U.S. presidential election, which is not only a political struggle between parties but also reflects the differences in values, economic interests, and awareness of climate issues among different groups in society. In general, the political polarization in the United States represented by the climate governance issue has not only led to chaos in domestic politics but also had a spillover impact on the world. Initially, the divergence between the two parties on climate issues has led to an oversimplification and one-sidedness in the public’s perception of environmental matters. Climate governance and environmental protection are inherently scientific issues. However, in their quest for electoral victory, the two parties have politicized these issues, framing them as a dichotomous political matter. Consequently, in the context of this political polarization, the American populace has shifted its focus away from the intrinsic merits and faults of climate-related topics (Mu, 2022). Second, the polarized political and social realities at home have affected America’s attitude to global governance. The extreme opposition in the United States makes it difficult for political parties to get their planned policies out of Congress and implement policies that satisfy the vast majority of the people, resulting in extreme and capricious behavior of the United States when participating in global governance.

As a major crisis threatening the survival of all mankind, climate change has become one of the main issues of the international community. As one of the major emitters of carbon dioxide, the United States has a responsibility to take more aggressive action on climate change. However, due to the divergent positions of its internal political parties and increasing political polarization, the U.S. political system has in some ways prevented collective action on a national scale to address climate change. The difference in the attitude of the two parties on the climate issue in the United States will have a direct impact on the degree of participation of the United States in global climate governance, and then interfere with the process of global climate governance. The result of this Western-style democracy is worth warning.

ORCID

Jiajiong He  https://orcid.org/0009-0003-1375-8275

Tingge Wang  https://orcid.org/0009-0005-6942-8536