15.2.1 Contributions to Climate Change and Its Impacts

As the second largest national contributor globally of greenhouse gas emissions (CIAT 2019), the United States’ climate footprint is considerable. In 2019, the country’s total greenhouse gas emissions were an estimated 6,558.3 million metric tons CO₂ eq. (EPA GHG Inventory Data Explorer). Evaluating the emissions trend since the early 1990s, total greenhouse gas emissions steadily rose through the 1990s and first part of the 2000s, reaching a high point in 2007 that was 15.6 per cent higher than 1990 levels. Following 2007, emission levels generally declined but with more fluctuation between years. In 2019, they were 1.8 per cent higher than 1990 levels, and indicators of decline in 2020 were largely attributable to the global pandemic (EPA 2021).

Carbon dioxide remains the most prominent greenhouse gas emitted, accounting for about 80 per cent of total emissions in the last decade. The main sectoral sources of carbon dioxide are transportation and electric power generation. The electricity sector has experienced a greater decline in emissions due to increasing renewable energy production and shift from coal-fired to natural gas systems. The transportation sector, on the other hand, has remained centred on petroleum fuel and in recent years has produced more GHG emissions annually than the electricity sector (EPA 2021: ES-7).

Methane accounted for about 10 per cent of total greenhouse gas emissions in 2019 (EPA GHG Inventory Data Explorer), of which the primary sources are associated with energy production, agriculture, and livestock. Reported methane emissions have generally declined in the past few decades, decreasing by 7 per cent since 2005 and 18.1 per cent since 1990 (EPA 2021), although mounting evidence from increasingly sophisticated analyses indicates that federal estimates of these emissions routinely fall well below actual levels (Alvarez et al. Reference Alvarez, Zavala-Araiza and Lyon2018).

There are numerous ways that the USA already is, or increasingly will be, affected by the effects of climate change, many of which pose threats to the country’s current infrastructural, economic, and environmental systems. While the increase in temperature poses a nation-wide threat, different parts of the country are vulnerable to particular elements of climate change in different ways (US Global Change Research Program 2018). Coastal cities face the threat of sea level rise and need resilience and adaptation strategies for impacts to buildings and infrastructure. Increase in the severity and frequency of severe precipitation and weather events poses a large threat in the Midwest, while drought intensity in the Southwest is increasing (NASA 2020). The rise in intensity of severe weather events and natural disasters affects all areas of the USA, from forest fires in western states and flooding in the Midwest to hurricanes in southern states. Agricultural systems across the nation are facing changing growing conditions and regional shifts in growing seasons. Low-income groups are particularly vulnerable and disproportionately at risk from the effects of climate change. They tend to be more exposed to severe weather such as heat and cold or precipitation and drought events, and often lack resources easily accessible to respond or adapt to changing conditions or events.

15.2.2 Commitment Relating to Climate Change

The US Constitution divides responsibility for international agreements between executive and legislative branches, while denying states any formal role in these matters. It states that the president ‘shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur’. More than 1,500 treaties were approved in this manner during the first 200 years of the federation, with only twenty-one rejections, but ratification has subsequently become far more difficult. Environmental agreements such as the Law of the Sea Convention, the Montreal Aviation Protocols, and the Kyoto Protocol, among others, have been rejected or withdrawn, reflecting the challenges of securing Senate super-majorities in a body in which every state holds a pair of seats regardless of population. The United States ratified the 1988 Montreal Protocol on Ozone Depleting Substances and approved four subsequent amendments. Congress took a major step on HFC (hydrofluorocarbons) transition through adoption of 2020 legislation that placed the United States on a timetable consistent with international phase-down goals and ratified the Kigali Amendments in 2022.

This divide between governmental branches has greatly complicated full American engagement in climate-related treaties. President George H. W. Bush signed the Earth Summit agreement but refused to sign the 1992 Convention on Biological Diversity. His successor, President Bill Clinton, signed this convention in 1993, but was unable to secure Senate ratification, along with a growing body of other international agreements (Blomquist Reference Blomquist2002). This phenomenon repeated itself after the signing of the Kyoto Protocol, when the Clinton Administration never submitted Kyoto to the Senate for ratification given formidable opposition. In 2001, President George H. W. Bush formally withdrew the USA from the Kyoto process.

Congressional inability to ratify treaties led Obama to consider an alternative path, an executive agreement, whereby a president may articulate American support for international collaboration without Senate support for binding commitment. Both the Copenhagen Accord and Paris Agreement were negotiated by the Obama Administration with this in mind, as well as North American climate agreements with neighbouring Canada and Mexico (Riccucci Reference Riccucci2018). The executive agreement approach needed for American involvement contributed to the Paris shift toward emphasizing volunteered and non-binding emission reduction targets, or Nationally Determined Contributions (NDC). This flexibility allowed Obama to pledge under Paris that the United States would reduce its annual GHG emissions by 26-to-28 per cent from 2005 levels by 2025, without Senate ratification or supportive legislation (Milkoreit Reference Milkoreit2019).

America’s Paris NDC commitment relied heavily upon Obama executive actions – primarily electricity and transportation sector performance standards under the 1990 Clean Air Act, and a compilation of existing state emission reduction policies. Applicable state policies included carbon pricing (twelve states), renewable electricity standards (thirty states), energy efficiency standards (twenty-one states), and renewable fuel standards (thirteen states), among others. It also took advantage of major shifts in American electricity production from coal to natural gas produced through hydraulic fracturing. By including modest methane emission estimates, the administration could claim significant electricity sector emission reductions.

All recent administrations have continued to attend major multilateral and transnational climate deliberations. Absence of treaty status gave Trump latitude to withdraw from Paris without Congressional consultation, although the agreement’s withdrawal process meant that final departure could not occur until the very end of his term (Leggett Reference Leggett2019). This delay allowed the incoming Biden administration to restore American engagement in Paris upon taking office in 2021 and take an active role in the Glasgow COP meetings, although no effort was made to secure Senate ratification.

15.3.1 General Practice of American Federalism

American climate policy is forged and implemented within a system that blends federalism with formal separation of powers between executive, legislative, and judicial branches at both federal and state levels. American presidents and state governors have some structural similarities, operating alongside bicameral legislative chambers and multitiered courts. Their interaction has routinely generated conflict in the formation and implementation of American climate policy, including numerous policy reversals following initial adoption.

15.3.2 Climate Governance in the American Federal System

15.4.1 State Climate Change Action

By contrast with the federal government’s prolonged inability to produce climate legislation, many states have adopted and implemented both regulatory and more market-based climate mitigation policies. Most of these policies are specific to individual states, albeit with potential to diffuse through emulation and adaptation in other jurisdictions (Grumbach Reference Grumbach2018; Shipan and Volden Reference Shipan and Volden2021; Stokes Reference Stokes2020). Renewable electricity standards were first adopted in Iowa in 1991 and expanded to thirty states as of 2021 with seven others maintaining voluntary versions. There is also some precedent for multiple states to adopt and implement policies that can be formally linked across jurisdictional boundaries. In carbon pricing, for example, the Regional Greenhouse Gas Initiative (RGGI) features nine partnership states maintaining a regional cap-and-trade system focused on electricity sector emissions. Auction revenue is commonly allocated for state energy transition expenses (Raymond Reference Raymond2016). RGGI expanded in 2019–20, adding New Jersey and Virginia as formal members while North Carolina and Pennsylvania also considered joining.

States diverge widely in their willingness and capacity to develop climate policies. California leads the nation in population and ranks second in total greenhouse gases, with particularly large releases from its transportation and agricultural sectors. It has long been a national leader on environmental policy, particularly air quality issues that have proven particularly vexing, and it has long prodded other states and the federal government to take more aggressive stances (Vogel Reference Vogel2018). Substantial climate change engagement began in the early 1990s, and California maintains a multisector cap-and-trade programme (operated jointly with the Canadian province of Québec) that allocates auction revenues for climate mitigation and adaptation. California also implements a wide range of renewable energy, energy efficiency, and biofuels programmes, often delegating considerable administrative authority to the formidable California Air Resources Board.

In turn, Texas leads the nation in total greenhouse gas emissions and ranks second in population. It has been a laggard in many climate policy areas and energy sector emissions have surged due to massive oil and gas production expansion since 2005 linked to hydraulic-fracturing techniques, particularly in the abundant Permian Basin. State leaders have long expressed doubts about the existence of climate change and have regularly led opposition to federal executive efforts to adopt climate policy. At the same time, Texas has abundant wind resources and has experienced substantial growth in its wind energy deployment, jumping from less than 1 per cent of total state electricity generation in 2000 to nearly 20 per cent in 2019. It has also invested heavily in renewable energy transmission infrastructure through fees added to electricity bills.

State policy divergence has greatly complicated federal attempts to use executive power to develop climate policy nationally, including Obama’s tenure. Alongside failure to consummate proposed cap-and-trade legislation in 2009, Obama advanced multiple administrative presidency initiatives linked to separate Clean Air Act provisions. All of these, including those focused on the electricity and transportation sectors, required extensive federal–state interaction and built on state model cases. They required extensive rule-making procedures set forth in federal legislation and could theoretically be adopted and implemented by EPA without Congressional input or approval (Belton and Graham Reference Belton and Graham2019). Collectively, they represented cornerstones in the Obama administration’s plan to achieve proposed Paris Agreement emission reductions just as they would subsequently under the Biden administration. States led by California actively inspired these efforts and actively endorsed them. States led by Texas actively opposed them, taking formal steps to reverse or undermine them.

For electricity, Obama sought to revise Clean Air Act provisions overseeing State Implementation Plans (SIPs) for compliance with various air emissions control requirements. This involved multiyear development of the Clean Power Plan (CPP). The power sector had already registered major emission reductions due to substantial coal-to-gas transition and numerous state policies promoting renewables. The nation was already heading towards net emission reductions in the sector greater than the overall 26-to-28 per cent levels established nationally under the Paris process. The CPP was intended to ensure that it exceeded those targets, compensating for other sectors less likely to achieve such extensive reductions. Each state was given a numeric emissions reduction target set federally. Many states that had already made or planned for major reductions were given more modest reduction targets and they generally proved supportive of the CPP. Many others generally opposed the very idea of a federally mandated CPP, particularly once they received more demanding reduction targets.

For transportation, the Obama administration embraced unilateral California legislation as a driving force behind a national strategy to reduce vehicular carbon emissions. Under federal air quality legislation first adopted in 1967, California was given unique authority to seek federal waivers in cases when it wanted to set higher vehicle emission standards than federal ones. Waivers are not formally established in the federal Constitution but have emerged as an intergovernmental tool that can allow or encourage one or more states to pursue policy innovation, including the case of mobile sources where single-state innovation has prompted regional and then national policy adoption. Waivers have not, however, been widely used in other areas of climate policy. The vehicle emissions case reflected California’s acute air quality issues linked to transportation and its active policy development in this area long before initial federal legislation (Vogel Reference Vogel2018). On more than 120 occasions since the late 1960s, California waiver requests were approved by EPA. At that point, other states are allowed, under 1977 provisions, to adopt the California standard. This so-called federalism ‘bandwagon effect’ regularly created momentum whereby the federal government ultimately harmonized its national standards with those of California and allied states (Carlson and Burtraw Reference Baldwin, Carley and Nicholson-Crotty2019). The Obama administration worked independently of Congress to embrace the California carbon waiver and merge it with separate federal fuel economy standards that pre-empted state action, thereby setting ambitious tailpipe emission reduction targets for multiple vehicle classes.

15.4.2 Adoption versus Implementation, and Policy Evolution

Implementation of these two federal attempts to use executive power through distinct federalism strategies for climate mitigation proved highly contentious, reflected in aggressive opposition from many states. In the CPP, more than a dozen Republican state attorneys general filed suit in federal court within days of final rule issuance. They claimed that the CPP represented an unconstitutional reinterpretation of air quality legislation that did not address climate. They contended that it outlined remedies linked not only to energy production but ‘outside-the-fence’ considerations, ultimately designed to eliminate fossil fuel use without legislation. This state opposition coalition eventually expanded to Texas and twenty-six other states, primarily jurisdictions with Republican leadership and significant production and use of fossil fuels within their boundaries. In contrast, California and seventeen other states, primarily with Democratic leadership and less-intensive carbon profiles, embraced the CPP. These states contended that CPP compliance would be highly feasible given growing renewable energy cost-competitiveness and could contribute significantly to American climate mitigation efforts.

This executive strategy drew no formal Congressional response but faced an unusual Supreme Court stay, suspending implementation until after 2016 elections. Trump’s election generated an executive order launching CPPs replacement with a far more modest Affordable Clean Energy rule that was suspended by a federal court in 2021. It was generally expected to have negligible impact on reducing emissions and may have actually increased them in some states through extended coal plant operation (Keyes et al. Reference Keyes, Lambert and Burtraw2019). However, it faced its own durability challenges in the Biden administration.

Trump was not as outspoken during his campaign against the vehicle emissions programme as the CPP. But his administration took rapid steps to begin the unprecedented process of reversing the waiver that California (and bandwagon states) had received, substituting a far more modest plan that precluded any state role through federal pre-emption of the process. Trump elevated his waiver opposition to a particularly intensive level upon learning that four major vehicle manufacturers pursued quiet negotiation of higher standards with California, including vulgar presidential diatribes and threats against these firms and the state. As with CPP, Trump did not entirely eliminate Obama’s regulatory effort but rather reconfigured it, producing more modest emission reduction targets and more flexible implementation. This approach would make it difficult for any successor to reverse it, while constraining state influence on policy design. Nonetheless, Trump efforts were not finalized prior to Biden administration arrival, which moved to restore the earlier waiver and build upon it in advancing its own executive climate strategy.

15.4.3 Factors Facilitating or Hindering State Actions

The federal government role on climate policy has largely remained confined to the executive branch with occasional court engagement. This reflects long-standing legislative branch inability to adopt climate or environmental legislation regardless of partisan control of Congress. The cases demonstrate limits that individual presidents and administrations face in advancing far-reaching policies that can be implemented and prove durable. The federal government has not created intergovernmental revenue transfer to encourage or support state energy transition policies or invested in boosting state implementation capacity. States nonetheless retain considerable latitude to either develop their own policies or take individual or collective action to either support or oppose federal initiatives. The case studies suggest that states may be more successful at blocking initiatives that they dislike rather than fully implementing them.

15.4.4 State Compensatory or Pre-emptive Action

California exemplifies Martha Derthick’s (Reference Derthick and Rabe2010) notion that states might take policy action to compensate for the absence of federal engagement, attempting to address their own emissions and also provide an example or model that can be emulated by other states or the federal government. In transportation, we see California’s ongoing efforts to compensate for the slow pace of federal regulatory reforms on vehicle emissions, employing its unique waiver authority to force national consideration of carbon-sensitive standards.

Many other states have also attempted to play this type of role. In carbon pricing, RGGI formation and expansion reflected concern from participating states about federal disengagement as well as desire to create a model that could inform future federal policy. Much of the state work that contributes to the US Climate Alliance was intended to fill the gap left by the Trump administration withdrawal from Paris and reversal of Obama administration regulatory programmes (Hultman, et al. Reference Hultman2019).

15.4.5 State Attention to Local Expertise and Circumstances

American local governments, particularly medium-to-large cities, have made considerable efforts to address both climate mitigation and adaptation in recent decades (Hughes Reference Hughes2019). They face many formal limitations, however, lacking independent constitutional authority and often reliant upon state interpretation of their potential taxation and regulatory powers. Nonetheless, local governments have regularly launched climate action plans that focus on areas of influence such as building standards and public transportation. Five hundred and thirty-four American cities, counties, and tribes, including some from every state, pledged fealty to Paris reduction targets. States have not, however, consistently drawn upon local expertise or unique circumstances in developing their own climate policies, reflecting a broader pattern of state–local tension in American politics. This reflects state trends in recent decades to reduce financial transfers from revenue-sharing programmes for local government as they contended with their own fiscal challenges, including the decade following the Great Recession.

In the case of California, local government climate engagement has been considerable, and some dimensions of state policy involve local or regional entities. The state’s far-reaching air quality efforts include considerable delegation of authority to local air quality districts for monitoring and compliance oversight. These bodies have played some role in climate policy implementation as well, and the state has also channelled significant cap-and-trade auction revenue to local governments, placing a growing emphasis in the past decade on disadvantaged communities that may lack resources to mount their own mitigation and adaptation strategies. This pattern is also evident in many of the RGGI cap-and-trade states and their evolving use of auction revenue in local communities. In many other states, localities with a strong climate interest may be well ahead of their state in commitment and capacity and so have to act unilaterally, albeit with formal limitations on their authority.

15.4.6 Horizontal and Vertical Convergence and Divergence

The divergent paths of American states over past decades on climate change can be demonstrated in part by distinguishing three distinct directions that clusters of states have pursued (Hultman et al. Reference Hultman2019, 19–20). ‘First-mover’ states routinely adopt new policies and have created a medley of policy responses over time. These represent 45 per cent of the total population but only 33 per cent of total greenhouse gases. California is a leading first-mover, joined by other states with predominant Democratic Party control and relatively limited oil and gas production capacity. ‘Fast-follower’ states lack a steady pattern of early adoption but often emulate leader states over time. These states represent 20 per cent of the total population and 20 per cent of total greenhouse gases. ‘Slow-follower’ states tend to delay or resist climate policy adoption. These states represent 35 per cent of the total population but 47 per cent of total greenhouse gases. Texas is the leading example, joined by a number of other states with predominantly Republican Party control as well as significant fossil fuel reserves and production.

Comparable categories can be used to divide the ways that states either formally oppose or support proposed federal policies through litigation. This suggests a significant divergence among subsets of states, one that may remain fairly consistent over time but can shift if partisan control changes or other factors emerge. Earlier expectations that significant first-mover efforts in the early 2000s would foster widespread ‘horizontal diffusion’ of multiple policies have largely not been realized, despite a long-standing American history of diffusion of environmental and other policy innovations over the last century (Baldwin, Carley, and Nicholson-Crotty Reference Baldwin, Carley and Nicholson-Crotty2019; Karch Reference Karch2007; Shipan and Volden Reference Shipan and Volden2021). Neither have earlier projections that a critical mass of states might adopt a climate policy and then tip the federal government into adopting this policy on a national basis via ‘vertical diffusion’ (Posner Reference Posner and Rabe2010).

In turn, not all state climate policies endure, reflected in cases of ‘reverse diffusion’ following initial adoption. Carbon cap-and-trade was adopted in two Northeastern states in the early 2000s but spread by 2010 to twenty-three states lodged in regions of the Northeast, Midwest, and Pacific West. This was widely seen as setting the stage for additional horizontal diffusion and eventual federal vertical diffusion that would build on these experiences, but political support quickly ebbed. Thirteen states subsequently withdrew, including many in the Midwest and Mountain West, although there was a slight uptick a decade later. These reversals reflected Congressional rejection of cap-and-trade, increased oil and gas production, intensified state partisan cleavages, and shifts from Democratic to Republican control in many states (Rabe Reference Rabe2018).

15.4.7 Climate Governance Conflict and Cooperation

Intergovernmental patterns of conflict and cooperation have waxed and waned over the course of recent decades. In general, federal–state conflict differs significantly depending upon partisan control of the presidency and Congress at a given time (Karapin Reference Karapin2020; Rabe Reference Rabe2011). In instances where Republicans dominate the federal government, states tend to more actively pursue their own climate policy development and challenge federal pre-eminence. These can be considered periods of ‘state domination’ whereby they attempt to fill perceived gaps in federal engagement and often find themselves in conflict with federal authorities. During Democratic presidencies, however, the tables turn. State climate policy development can slow in anticipation of new federal policies, as they did during the Obama presidency. Many Republican states entered into formal opposition to federal policy initiatives during this period, including litigation.

There is considerable opportunity for state clusters to cooperate in the American federal system, including inter-state compacts that the Constitution allows with Congressional consent (Bowman Reference Bowman2004). These historically have involved numerous policy areas, including water quality and energy production. No such compacts have been approved in recent decades related to climate change and two regional cap-and-trade initiatives either disappeared or withered. However, RGGI has proven a durable regional programme that has endured major adjustments in its emissions cap, implementation of an auction-and-invest system for revenue use, and membership changes (Raymond Reference Raymond2016).

15.4.8 Coercion, Collaboration, Competition, and Emulation in Climate Policy

The CPP represents a leading example of an executive effort to develop a federal climate strategy to operate with considerable room for single or multistate innovation. The CPP adapted the Clean Air Act state implementation plan process that sets federal standards but gives states considerable latitude to develop their preferred response, working either independently or collaboratively with neighbouring states. As long as the federal government was satisfied that a state had developed a credible plan, it would delegate implementation authority to the lead state agencies, much as had been done for conventional pollutants (Carlson and Burtraw Reference Carlson and Burtraw2019).

Multistate collaboration offered one alternative for states to work together, likely through creation of cap-and-trade systems comparable to RGGI. This would draw on prior RGGI lessons and considerable state experience operating an emissions trading system for sulphur dioxide, offering a flexible path to minimize compliance costs for regulated parties and states. Federal officials outlined this option in early briefings around the nation with state officials. There was also an option of competition whereby each state would design its own strategy, using cap-and-trade or other performance-based compliance options. Under this model, each state would receive its emissions reduction target but select its preferred option and thereby try to out-compete neighbours in containing compliance costs. Finally, there was considerable expectation that either collaborative or competitive strategies would ultimately foster policy emulation, as states learned from their experiences over time given their divergent approaches, ultimately adapting and refining their state implementation plans.

In the end, none of these aspirations were achieved, given the aggressive state political opposition that emerged, leading to the 2016 court-mandated implementation freeze and followed by a federal executive transition that eviscerated the programme. The Obama administration launched the CPP with the implicit assumption that the president would be succeeded by a supportive Democrat committed to seeing it into full implementation. Opposition states played a pivotal role in CPP downfall, alleging that it represented federal coercion of federal legislation designed solely to reduce conventional air contaminants, although the federal courts and national election results dealt the death blows. The Biden administration faced the challenge of revisiting Clean Air Act application to electricity sector carbon emissions once it became clear in 2021 that Congress opposed a federal clean electricity standard despite its widespread state use.

15.4.9 Policy Divergence or Convergence and Dynamics of Conflict and Cooperation

Full implementation of existing and emerging state policy commitments as portions of a federal strategy may move the United States within striking distance of initial Paris reduction targets despite federal policy disengagement. However, state-led action alone would not enable the nation to approach Biden era emission reduction proposals for 2030. Innumerable effectiveness, equity, and efficiency questions continue to emerge in examining the American emissions trajectory and likely future course, barring a major shift towards emboldened federal policy. These equity challenges include the general absence of a consistent carbon pricing strategy or a sustained funding source for energy transition as well as enormous differences in the costs of electricity and energy in various states and regions. The state-driven American experience demonstrates that climate policies can serve to reduce emissions but only in an uneven matter that exacerbates broader American political and economic challenges (Kettl Reference Kettl2020). These factors have served to accentuate concerns in the United States over climate and energy justice, particularly for communities that have long faced substantial environmental threats and lack resources to address them.