Hannah Wiseman, Penn State The U.S. Supreme Court in March 2025 ended a decade-old lawsuit filed by a group of children who sought to hold the federal government responsible for some of the consequences of climate change. But just two months earlier, the justices allowed a similar suit from the city and county of Honolulu, Hawaii, to continue against oil and gas companies. Evidence shows that fossil fuel companies, electric utilities and the federal government have known about climate change, its dangers and its human causes for at least 50 years. But the steps taken by fossil fuel companies, utilities and governments, including the U.S. government, have not been enough to meet international climate targets. So local and state governments and citizens have asked the courts to force companies and public agencies to act. Their results have varied, with limited victories to date. But the cases keep coming.

Attacking the emissions themselves

In general, legal claims in the U.S. can be based on the U.S. and state constitutions, federal and state laws, or what is called “common law” – legal principles created by courts over time. Lawsuits have used state and federal laws to try to limit greenhouse gas pollution itself and to seek financial compensation for alleged industry cover-ups of the dangers of fossil fuels, among many other types of claims. In 2007 the U.S. Supreme Court determined that greenhouse gases such as carbon dioxide emitted from motor vehicles were a “pollutant” under the federal Clean Air Act. As a result, the court ordered the Environmental Protection Agency to either determine whether greenhouse gases from new vehicles contribute to climate change, and therefore endanger human health, or justify its refusal to study the issue. In 2009 the EPA found that carbon dioxide emissions did in fact endanger human health – a decision called the “endangerment finding.” In 2010 it imposed limits on carbon dioxide emissions from new vehicles and, later, from newly constructed power plants. But related EPA efforts to regulate emissions from older power plants – the ones that emit the most pollution – failed when challenged in court on the grounds that they went too far in limiting emissions beyond the power plants’ own properties. The Biden administration had finalized a new rule to clean up these older plants, but the Trump administration is now seeking to withdraw it. The Trump administration is also now beginning the complicated process of reviewing the 2009 endangerment finding. It could try to remove the legal basis for EPA greenhouse gas regulations.

A common-law approach

In response to this federal executive seesaw of climate action, some legal claims use a court-based, or common law, approach to address climate concerns. For instance, in Connecticut v. American Electric Power, filed in 2004, nine states asked a federal judge to order power plants to reduce their emissions. The states said those emissions contributed to global warming, which they argued met the federal common law definition of a “public nuisance.” That case ended when the U.S. Supreme Court ruled in 2011 that the existence of a statute – the federal Clean Air Act – meant common law did not apply. Other plaintiffs have tried to use the “public nuisance” claim or a related common-law claim of “trespass” to force large power plants or oil and gas producers to pay climate-related damages. But in those cases, too, courts found that the Clean Air Act overrode the common-law grounds for those claims. With those case outcomes, many plaintiffs have shifted their strategies, focusing more on state courts and seeking to hold the fossil fuel industry responsible for allegedly deceiving the public about the causes and effects of climate change.

Examining deception

In many cases, state and local governments are arguing that the fossil fuel industry knew about the dangers of climate change and deceived the public about them, and that the industry exaggerated the extent of its investments in energy that doesn’t emit carbon. Rather than directly asking courts to order reduced carbon emissions, these cases tend to seek damages that will help governments cover the costs associated with climate change, such as construction of cooling centers and repair of roads damaged by increased precipitation. In legal terms, the lawsuits are saying oil and gas companies violated consumer-protection laws and committed common-law civil violations such as negligence. For instance, the city of Chicago alleges that major petroleum giants – along with the industry trade association the American Petroleum Institute – had “abundant knowledge” of the public harms of fossil fuels yet “actively campaigned” to hide that information and deceive consumers. Many other complaints by states and local governments make similar allegations. Another lawsuit, from the state of Maine, lists and provides photographs of a litany of internal industry documents showing industry knowledge of the threat of climate change. That lawsuit also cites a 1977 memo from an Exxon employee to Exxon executives, which stated that “current scientific opinion overwhelmingly favors attributing atmospheric carbon dioxide increase to fossil fuel consumption,” and a 1979 internal Exxon memo about the buildup of carbon dioxide emissions, which warned that “(t)he potential problem is great and urgent.” These complaints also show organizations supported by fossil fuel companies published ads as far back as the 1990s, with titles such as “Apocalypse No” and “Who told you the earth was warming … Chicken Little?” Some of these ads – part of a broader campaign – were funded by a group called the Information Council for the Environment, supported by coal producers and electric utilities. Courts have dismissed some of these complaints, finding that federal laws overrule the principles those suits are based on. But many are still winding their way through the courts. In 2023 the Supreme Court of Hawaii found that federal laws do not prevent climate claims based on state common law. In January 2025 the U.S. Supreme Court allowed the case to continue.

Other approaches

Still other litigation approaches argue that governments inadequately reviewed the effects of greenhouse gas emissions, or even supported or subsidized those emissions caused by private industry. Those lawsuits – some of which were filed by children, with help from their parents or legal guardians – claim the governments’ actions violated people’s constitutional rights. For instance, children in the Juliana v. United States case, first filed in 2015, said 50 years of petroleum-supporting actions by presidents and various federal agencies had violated their fundamental “right to a climate system capable of sustaining human life.” The 9th U.S. Circuit Court of Appeals ruled that their claim was a “political question” – meant for Congress, not the courts. The U.S. Supreme Court declined to reconsider that ruling in March 2025. But children in Montana found more success. The Montana Constitution requires state officials and all residents to “maintain and improve a clean and healthful environment … for present and future generations.” In 2024 the Montana Supreme Court determined that this provision “includes a stable climate system that sustains human lives and liberties.” The Montana Supreme Court also reviewed a state law banning officials from considering greenhouse gas emissions of projects approved by the state. The court found that the ban violated the state constitution, too. Since then, the Montana Supreme Court has specifically required state officials to review the climate effects of a project for which permits were challenged. Concerned people and groups continue to file climate-related lawsuits across the country and around the world. They are seeing mixed results, but as the cases continue and more are filed, they are drawing attention to potential corporate and government wrongdoing, as well as the human costs of climate change. And they are inspiring shareholders and citizens to demand more accurate information and action from fossil fuel companies and electric utilities. Hannah Wiseman, Professor of Law, Penn State This article is republished from The Conversation under a Creative Commons license. Read the original article.