Attribution Science

Also see Scientific evidence that can be used in litigation

The basics
Attribution science is the study of a causal chain between the emission of greenhouse gases into the atmosphere, the phenomena of global climate change, and the localized impacts that cause specific climate related harms. Establishing this causal chain is often necessary to overcome one of the largest hurdles to climate change litigation, avoiding dismissal because of a lack of standing or because the issue was deemed non-justiciable. Fortunately, advances in attribution science have allowed scientists to better understand the link between greenhouse gas emissions and extreme weather events.

The case Lliuya v. RWE provides an example of how attribution science can open the door for climate litigation. The case involved a complex causal chain, from a German energy company emitting greenhouse gases over decades, to global climate change causing the accelerated melting of glaciers in the Peruvian Andes, to the swelling of a glacial lake that threatened the home of a Peruvian farmer. Although the German court initially ruled that no “linear causal chain” could be discerned amid the complex components, an appeals court allowed the case to proceed to the evidentiary phase. A case such as this would not be possible without science to tie RWE's emissions to a specific harm caused to a specific person.

Source Attribution: Tying Emitters to Emissions
Attribution science tying emissions to specific emitters has advanced significantly in the last decade. It has been shown that nearly two-thirds of carbon dioxide emitted since the 1750s can be traced to the 90 largest fossil fuel and cement producers, most of which still operate today. By quantifying the contribution of each of these Carbon Majors to climate change, it provides the first step to holding them liable for their emissions. In Lliuya, the plaintiff sought 0.47% of the cost of adapting to the melting glaciers, the same percentage as RWE’s estimated contribution to global industrial greenhouse gas emissions since the beginning of industrialization.

Impact Attribution: Tying Emissions to Impacts
Once an emitter has been tied to a percentage of greenhouse gas emissions, the next step is to determine the impact of those emissions. Researchers have estimated the contribution to global surface temperature increase and global sea level rise of the largest carbon emitters. This work lays the groundwork for tracing emissions sourced from industrial carbon producers to specific climate impacts. Specifying these impacts and tracing the causal chain from emission to impact is essential for the success of lawsuits against fossil fuel companies and other emitters.

Attributing your event
Attribution science is the science that allows to determine with what probability such an event is due to human emissions of greenhouse gases. Some events are easier to attribute than others (see graphic).

Colleagues at the Oxford Environmental Change Institute and others are working on real-time attribution of events as they unfold. Check the Climate Attribution Database and World Weather Attribution to see if there is some work available for an event you are looking at. A recommended read is: The science of attributing extreme weather events and its potential contribution to assessing loss and damage associated with climate change impacts. (ECI & University of Oxford)

Flood Hazard from Lake Palcacocha
The frequently referenced climate litigation case Lliuya v. RWE concerned flood risk from Lake Palcacocha in the Peruvian Andes. In Increased outburst flood hazard from Lake Palcacocha due to human-induced glacier retreat, the authors evaulate the anthropogenic contribution to the swelling of Lake Palcacocha and the associated increased risk to the town of Huaraz. They found that it is virtually certain (>99% probability) that the retreat of Palcaraju glacier to the present day cannot be explained by natural variability alone.

Attribution of extreme rainfall from Hurricane Harvey
During August 25–30, 2017, Hurricane Harvey stalled over Texas and caused extreme precipitation, particularly over Houston and the surrounding area on August 26–28. This resulted in extensive flooding with over 80 fatalities and large economic costs. Extrapolating these results to the 2017 event, we conclude that global warming made the precipitation about 15% (8%–19%) more intense, or equivalently made such an event three (1.5–5) times more likely. This analysis makes clear that extreme rainfall events along the Gulf Coast are on the rise. With these scientific studies it can be verified why, and how natural phenomena have intensified, and that global warming is causing it.

Resources

 * Smoke and Fumes: The Legal and Evidentiary Basis for Holding Big Oil Accountable for the Climate Crisis. (Center for International Environmental Law, 2017)
 * Interactive Map - Attributing extreme weather of climate change (Carbon Brief, 25 February 2021)

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