National fossil fuel companies, public utilities and other State entities are responsible for vast amounts of greenhouse gas emissions. The pollution of these State entities represents a substantial departure from the due diligence standards of international law. This article evaluates the promise of international climate litigation against State pollution sources, or international 'State-as-polluter' litigation, as a tool to overcome the gap between international norms and State conduct. The analysis shows that the conduct of State-controlled polluters may be attributable to States in certain situations. It further suggests that States can incur international responsibility for their failure to comply with heightened due diligence obligations in relation to Statecontrolled polluters. 1 | INTRODUCTION It is an often-neglected fact that States are directly responsible for much of the world's greenhouse gas (GHG) emissions. A wide range of State actors, including State-owned electricity utilities, armed forces and other State actors in the Global North and South, consume vast amounts of fossil fuels for electricity generation, transportation and heavy industry. 1 State-owned energy companies, in particular, are responsible for a lion's share of global emissions. Recent attribution studies have quantified the immense emissions of State-owned actors, such as Saudi Aramco, Russia's Gazprom, China National Offshore Oil Corporation, Norway's Equinor, Mexico's Pemex and the fossil fuel industries of most members of the Organization of the Petroleum Exporting Countries (OPEC). 2 Stateowned enterprises accounted for 59 percent of carbon majors' emissions in 2017 3 and roughly 69 percent of carbon majors' emissions from 1910 to 2010. 4 As climate change intensifies, State-owned fossil fuel producers and consumers will play a decisive role in meeting our global temperature limits. 5 By one estimate, 28 State-owned enterprises and eight national coal industries have the combined capacity to exhaust 143 percent of the remaining 2 C global carbon budget. 6 State-caused pollution represents a substantial departure from international norms. States are bound by the customary no-harm rule, which entails an obligation to prevent significant transboundary harm from State entities and private actors. 7 Similarly, the Human Rights Committee noted that the implementation of the right to life depends on 'measures taken by States parties to preserve the environment and protect it against harm, pollution and climate change caused by public and private actors'. 8 State parties to the United Nations Framework Convention on Climate Change (UNFCCC) agreed to 'protect the climate system' and ensure the 'stabilization of greenhouse gas 1