2 C E N T E R F O R I N T E R N AT I O N A L E N V I R O N M E N TA L L AW Introduction C limate change poses a fundamental threat to ecosystems, nations, human rights, and human lives. It is caused by the emission and accumulation of greenhouse gases in the atmosphere, primarily due to the combustion of fossil fuels—oil, gas, and coal. This report was written to answer the questions: What did the fossil fuel companies know? When did they know it? What did they do about it? For what can they be held legally and morally responsible? ©skeeze/Pixabay The report begins by exploring the fundamental principles of legal responsibility in both tort and human rights law. The objective is not to assess the elements of a particular claim, but to distill the core components of legal responsibility from tort and human rights law that underpin the allocation of liability across an array of legal domains and legal systems. We then review the factual background of the petroleum industry’s knowledge and awareness of climate change. We present the best available evidence documenting the petroleum industry’s understanding of climate change at critical moments throughout the twentieth and into the twenty-first centuries, along with research the industry conducted into alternative explanations for observed climatic changes and potential carbon emissions solutions. Finally, we offer examples of actions taken by the industry to confuse or mislead the public. The evidence in this report comes from several sources, including the Center for International Environmental Law (CIEL), Climate Investigation Center’s Climate Files, InsideClimate News, Union of Concerned Scientists, Los Angeles Times and Columbia School of Journalism, DeSmog Blog, Corporate Europe Observatory, and others. A more detailed description of these sources, their limitations, and their treatment in this synthesis is set forth as Annex II to this report. To facilitate direct access to relevant evidence, hyperlinks to cited documents have been provided wherever feasible. At the time of publication (Nov. 2017) all hyperlinks were functional and accurate, although some linked documents are subject to paywalls or other limitations.