4 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 demonstrated that more than half of global CO2 emissions since 1988 can be linked to just 25 producers, including five leading investor-owned oil companies: ExxonMobil, Shell, BP, Chevron, and Total.11 If Saudi Arabia carries out its plan to list state-owned Saudi Aramco on a public stock market, Aramco would join the other investor-owned companies on this list. © Aaron Sprecher/Greenpeace In September 2017, researchers from the Union of Concerned Scientists (UCS) and Oxford University collaborated with Heede to combine these fields of attribution science for the first time. The researchers disaggregated major carbon producers’ historical emissions by year and constructed emissions profiles for each company over time.12 By tracing emissions through time, the team was able to attribute fractions of the accumulation of carbon dioxide in the atmosphere, increases in atmospheric temperature, and elevation of the sea level to individual companies based on the timing of their commercial activities. Just as significantly, the paper demonstrated how hundreds of excess deaths from a single extreme weather event could be attributed to climate change and ultimately, in part, to the oil, gas, and coal produced by major carbon producers.13 This new research is a leap forward in attribution science. Heede’s original research was groundbreaking in that it tied significant fractions of global emissions to individual companies or state actors. Now, UCS, CAI, and Oxford have demonstrated that scientists (and plaintiffs) can trace the contributions of individual companies to climate impacts and climate-related disasters. While the specific mathematic conclusions may be challenged, the fact that this research and methodology passed the muster of peer review demonstrates that it is possible to apportion percentages of specific climate impacts to individual companies. But establishing that major carbon producers are causally contributing to climate impacts and climate harms is only the first step in accountability. The question remains: Can they be held responsible? The Fundamental Elements of Responsibility: Notice of Risk and the Opportunity to Avoid or Reduce Risk While establishing causal links between a defendant’s actions and a plaintiff ’s harms is a necessary condition of liability in most circumstances, it is rarely sufficient. There are certain areas of law and certain legal concepts—such as strict liability— This research and methodology demonstrates that it is possible to apportion percentages of specific climate impacts to individual companies. under which proof of causation alone will trigger liability. Far more generally, however, as a matter of fairness, morality, and of law, judicial bodies seek evidence that a defendant not only caused a harm, but that they were culpable for that harm in some way—that the defendant acted (or failed to act) in a way that renders them morally responsible for addressing—and remedying—the consequences of those actions. As ethicist Henry Shue explains in an essay that accompanied the foregoing paper: If A falls down the escalator because she is hit from behind by B, but B was tripped by C, B is partly causally responsible but not at all morally responsible for A’s fall. The moral responsibility for A’s fall belongs entirely to C. Causal responsibility must be blameworthy to become the basis for moral responsibility, and causation—or “contribution”—is blameworthy only if it is a violation of a socially accepted principle.14