Consistency on climate change in the US courts but a ‘swinging pendulum’ in government
The United States Environmental Protection Agency recently rescinded the Greenhouse Gas Endangerment Finding which had concluded that greenhouse gas emissions are air pollutants under the Clean Air Act, contributing to pollution that endangers public health or welfare. Lord Carnwath CVO, former UK Supreme Court justice, provides a critical perspective on this move within the wider context of climate change litigation and policies in the US.
As a British judge with a special interest in environmental law, over the last two decades I have taken a particular interest in how the courts are responding to the challenges posed by climate change. This commentary scrutinises significant developments over that period in the United States. We have gone from the ground-breaking decision of the Supreme Court in Massachusetts v. EPA, which formed the basis of a strong Greenhouse Gas Endangerment Finding by the Environmental Protection Agency in 2009, and the central role of the US in securing the critical Paris Agreement in 2015; to the election in 2024, for the second time, of President Donald Trump, who professes to regard climate change as a “hoax”, leading to the recent decision of the EPA to rescind the Endangerment Finding on the basis that it never had the power to make it in the first place. As an interested legal observer, my reactions have moved from admiration, through frustration, to incomprehension and near-despair.
Courts in the US consistently recognise the reality of climate change
Regardless of the changing positions of successive Presidents, the US courts have been unequivocal in their recognition of the reality of climate change and its causes, and of the responsibility of government to address it. This was made clear in the Supreme Court’s 2007 decision in the Massachusetts v. EPA case. The language of the majority judgment was uncompromising when it recorded without dissent the claimants’ assertion that global warming was “the most pressing environmental challenge of our time”. The judgment charted the development of a strong international consensus that global warming threatens “severe and irreversible changes to the natural ecosystem” and swept aside the EPA’s arguments that emissions from American traffic made a relatively insignificant contribution to the global problem.
In November 2016, another strong legal decision, this time by the US District Court of Oregon in Juliana v. United States, refused to strike out a claim brought by young citizens against the government for failing to protect them from the negative impacts of climate change. The court held that the right to a climate system capable of sustaining human life is fundamental to a free and ordered society and is protected by the Due Process clause of the US Constitution and the Public Trust doctrine. Although the claim was ultimately dismissed by the majority in 2020, there was no disagreement over the factual basis, with the court noting that, “a substantial evidentiary record documents that the federal government has long promoted fossil fuel use despite knowing that it can cause catastrophic climate change.” Judge Staton’s minority judgment records this consensus in starker terms: “The government accepts as fact that the United States has reached a tipping point crying out for a concerted response—yet presses ahead toward calamity.” The reasons for refusing relief concerned the limits of the court’s constitutional role; any effective plan would require complex policy decisions entrusted to the executive and legislative branches of government.
Another striking example of US case law came in the December 2024 decision of the Montana Supreme Court in Held v. State of Montana. Fossil fuel production is central to the state’s economy, yet Montana is also one of only three US states with express constitutional protection for environmental rights, guaranteeing citizens “the right to a clean and healthful environment”. In the Held case, a group of young citizens challenged, among other things, a provision in the Montana Environmental Policy Act that prohibited the state from considering greenhouse gas emissions when deciding whether to issue permits for energy-related projects. The court held that this violated the public’s constitutional right to a clean and healthful environment. It is notable that even in a state as supportive of fossil fuel extraction as Montana, there was no attempt to challenge the “overwhelming scientific evidence and consensus” on the reality and scale of addressing climate change. Echoing the Supreme Court in the Massachusetts v. EPA decision, the court also rejected so-called “drop in the ocean” arguments, or that Montana’s permitted greenhouse gas emissions were insignificant when evaluated against global emissions.
Government responses to climate change have changed dramatically with each administration
The US government’s response to climate change has been markedly less consistent than the courts’. Even the Chief Executive of ExxonMobil, Darren Woods, has complained about the uncertainty and inefficiency caused by having “the pendulum swing back and forth as administrations change” (as reported at the UN Climate Conference, COP29, in November 2024). The Massachusetts judgment in 2007 came under the last Bush administration and there was little immediate policy response. However, following the 2008 change of government, the majority judgment paved the way for radical changes to the EPA, leading in December 2009 to a formal ‘Endangerment Finding’ under the Act. The strong domestic policies made possible by the Massachusetts decision also strengthened President Obama’s hand internationally, leading in November 2014 to the U.S.–China Joint Announcement on Climate Change, through which the two Presidents committed their countries to working towards an agreed outcome “with legal force” at the UN Climate Conference in Paris, COP21, in 2015. That was achieved, and it seems fair to conclude that the international consensus which led to the Paris Agreement would never have happened without the Massachusetts v. EPA decision.
The global consensus suffered a setback in November 2016 with the first election of Donald Trump, followed in summer 2017 by his announcement of intended withdrawal from the Paris Agreement. He embarked on a series of executive orders designed to unwind his predecessor’s climate policies. To a legal observer, against the background of the Massachusetts judgment and the overwhelming international consensus in Paris, the apparent lack of any serious attempt to justify this dramatic policy reversal by reference to legal principle or scientific evidence was shocking. In November 2018, the government itself published its Fourth National Climate Assessment, documenting the devastating effects of climate change on the US and the need for urgent global action. The President’s reported response was that he “didn’t believe it”.
In 2021, a degree of rationality was restored to US climate change policy under the Biden administration when the country rejoined the Paris Agreement and played a leading role in the COP process. However, a second and more severe setback to climate policy has occurred with the second Trump presidency, which began in January 2025. One of the new President’s first acts was to initiate US withdrawal from the Paris Agreement under an Executive Order titled (bizarrely) “Putting America First in International Environmental Agreements”.
On 4 February 2025, the EPA’s website featured an interview with new Administrator Lee Zeldin, who echoed the President’s talk of “a climate change hoax” and announced that the EPA would pursue an agenda to “ditch the leftist environmentalist radicalism”, and drive “a dagger straight into the heart of the climate change religion”. In July 2025, the EPA published a proposed rule to rescind the 2009 Endangerment Finding and eliminate greenhouse gas emission standards for American motor vehicles and engines; the formal rule was then issued in February 2026.
In a document extending to over 100 pages, the reversal is justified on purported legal grounds. The EPA concluded it “lacks statutory authority to maintain this novel and transformative regulatory program,” claiming its actions “rested on a profound misreading” of the decision in the Massachusetts case. A “de minimis” argument was also advanced, claiming that the regulation of greenhouse gases would have “no material impact on global climate change concerns”. Notably, the final document does not attempt to argue that the scientific foundation of the endangerment finding was wrong.
Rescinding the EPA’s Endangerment Finding does not align with the science or facts of climate change
The repeal of the Endangerment Finding is already subject to legal challenge. Two further comments are worth making. First, it seems extraordinary to find a “de minimis” argument now being advanced, apparently as a point of law, given the force with which similar arguments were rejected by the majority judgment of the Supreme Court in 2007, and more recently by the Montana court in 2024. Secondly, and more generally, it seems little short of grotesque that a responsible public authority committed (as its website says) to addressing climate change should of its own motion seek to establish that its actions to that end, which have survived legal challenges for the last 17 years, were beyond its powers.
Furthermore, while the EPA’s website states that “understanding and addressing climate change is critical to EPA’s mission of protecting human health and the environment”, this commitment does not extend to telling us what, in practical terms, the EPA intends to do about it.
As the International Court of Justice noted last year in its landmark Advisory Opinion on the ‘Obligations of States in respect of Climate Change’, climate change is “an existential problem of planetary proportions that imperils all forms of life and the very health of our planet”. To paraphrase from the Opinion, if we are to secure a liveable future for ourselves and future generations, solutions to this problem require contributions from all fields of human knowledge, in addition to human will and wisdom, at the individual and political levels. If the EPA is indeed committed to providing “clear, accessible information” on climate change, then we should all look forward to finding on its website a clear statement of its position on the ICJ judgment, and the solutions it proposes to address the climate crisis.
The views in this commentary are those of the author and do not necessarily represent those of the Grantham Research Institute.
A more in-depth article on this topic by Lord Carnwath was published by the Sabin Centre blog ‘Climate Law’ on 22 April 2026.