<p class="wp-block-paragraph">Can one state’s law regulate another state’s natural environment? This question is currently being addressed in the Supreme Court, which is considering a case regarding whether two local governments in Colorado can ask a local state court to regulate climate change through state law. The case was brought by the city of Boulder and the county surrounding it, with similar lawsuits pending against the oil and gas industry in various state courts across the country. Plaintiffs in these cases assert that they are relying solely on state law, while defendants argue that only federal law can govern an interstate issue like carbon emissions.</p>
<p class="wp-block-paragraph">In a previous ruling in 2011, the Supreme Court rejected a climate case from Connecticut, stating that Congress adopted the Clean Air Act without granting a federal statutory right to bring such lawsuits, meaning federal judges cannot establish a federal “common law” right to sue.</p>
<p class="wp-block-paragraph">As a result, climate plaintiffs like Boulder have turned to state law in their local courts. Boulder’s lawyer argued that when Congress enacted the Clean Air Act, it displaced federal common law, leaving room for state law to apply. However, this perspective overlooks the principle that federal law governs interstate air and water matters because they are inherently interstate issues.</p>
<p class="wp-block-paragraph">For example, when a river crosses state borders, neither state can unilaterally claim rights to the water. If the states cannot resolve the issue through an interstate agreement approved by Congress, the Supreme Court will adjudicate water-rights disputes under federal law. The court has previously stated that neither state statutes nor decisions can be conclusive in such matters.</p>
<p class="wp-block-paragraph">The water cases illustrate a key error made by state-law plaintiffs: federal law governs these disputes because they are inherently interstate. Thus, even if federal common law is replaced by federal statute, there is no allowance for state law to intervene in this federal domain. In the ongoing water dispute between Florida and Georgia, for instance, the states litigated for years under federal law, resulting in two Supreme Court decisions that applied federal standards to the case.</p>
<p class="wp-block-paragraph">Similarly, in climate cases, state law cannot apply because greenhouse gases do not adhere to state boundaries. Congress has the authority to pass legislation that grants states some regulatory power over emissions within their borders. However, just as New Mexico cannot protect its water supply by banning irrigation in upstream Colorado, Boulder does not have the authority to regulate carbon emissions on a global scale. The Constitution designates certain issues, such as cross-border air and water disputes, for resolution by the national government.</p>
<p class="wp-block-paragraph"><em>William M. Jay is a partner at the law firm Paul, Weiss, Rifkind, Wharton & Garrison and chair of its Supreme Court and appellate practice. He has handled several water-related disputes in the Supreme Court and has filed briefs for the U.S. Chamber of Commerce in the Boulder litigation. This document was written in his personal capacity and not as a representative of any client.</em></p>