By Michael Burger and Jessica Wentz

As you know, in Juliana v. United States twenty-one individual youth plaintiffs filed a lawsuit in federal district court in Oregon against the United States, the president, and various other federal officials and agencies, claiming that the “nation’s climate system” is critical to their rights to life, liberty, and property; that the federal government has violated their substantive due process rights by allowing fossil fuel production, consumption, and combustion at “dangerous levels;” and that the government has failed to fulfill its obligations under the public trust doctrine. As a remedy, the plaintiffs asked the court to compel the government to develop a plan to reduce carbon dioxide (CO2) emissions so that atmospheric CO2 concentrations will be no greater than 350 parts per million by 2100 – a science-based target consistent with the goal of limiting global warming to 1.5 degrees C.

The plaintiffs’ attorneys at Our Children’s Trust have dubbed their case the “trial of the century.” The U.S. Department of Justice, under both the Obama and Trump administrations, has argued that no trial should take place at all. The district court denied the defendants’ motion to dismiss, finding that the plaintiffs had raised colorable constitutional claims; after initial discovery had been conducted, the court denied (in significant part) defendants’ motions for summary judgment and judgment on the pleadings, affirming the earlier decision that plaintiffs raised valid claims and finding genuine issues of material fact that warrant a trial. But, after repeated attempts by the government to gain interlocutory appeal at the 9th Circuit and the Supreme Court, the district court’s decisions denying the U.S. government’s dispositive motions will now be reviewed by the 9th Circuit. It is possible that the trial will never happen.

And so the question lingers: What would the “trial of the century” look like? What are the key scientific questions that the parties would seek to answer? Where would the points of agreement and contention lie? And how would all of this factor into determinations on the plaintiffs’ standing to bring their suit, and the nature and extent of the government’s responsibility? As it turns out, the two sides have produced a documentary preview of the potential answer. In preparation for trial, the plaintiffs submitted over one thousand pages of expert reports detailing the fundamental science of climate change, observed and projected impacts, and the ways in which the U.S. government and the fossil fuel industry have contributed to the problem. In response, the defendants submitted hundreds of pages of their own expert reports contesting the reliability, soundness and validity of the plaintiffs’ submissions. And in response to that, the plaintiffs submitted a Notice of Supplemental Disputed Facts to the court, arguing that between these two sets of documents various questions of material fact were in dispute, requiring a trial. With all of that in hand, the district court thought, and still thinks, a trial is warranted. In the remainder of this post, we summarize the key proffers and points of contention, providing a glimpse of at least part of what these, or other, plaintiffs’ day in court might eventually entail.

The Pleadings: Two Key Issues of Fact

Plaintiffs’ case, and their ability to bring their case to court, hinge on two factual issues: (1) the extent to which the U.S. government can be deemed responsible for greenhouse gas emissions that are causing anthropogenic climate change, and (2) the extent to which anthropogenic climate change is responsible for the specific injuries or harms suffered by the individual plaintiffs. In a major research project we are conducting with our colleague Radley Horton, a climate scientist at the Lamont-Doherty Earth Observatory, we define these concepts as “source attribution” (the attribution of anthropogenic climate change to specific sources) and “impact attribution” (the attribution of particular impacts to anthropogenic climate change).

In regards to source attribution, the plaintiffs in their Complaint emphasize the magnitude of the emissions at issue, noting that fossil fuel emissions from U.S. energy consumption had climbed from to 4.7 billion metric tons of CO2 in 1987 to 5.4 billion metric tons in 2014, and that if the government had acted on expert recommendations from the early 1990s on limiting CO2 emissions, it could have reduced emissions 35% from 1987 levels by 2015.

In regards to impact attribution, a substantial portion of the Complaint is dedicated to explaining how climate change is affecting and will affect plaintiffs’ lives, liberty, and property interests, to support both their standing to sue and the merits of their claims. The Complaint alleges existing and projected impacts on each of the individual youth plaintiffs, such as adverse impacts on a farm where one works and intends to pursue a livelihood; lost income for a family that works at a ski resort with dwindling snow; and asthma attacks from the increased frequency of forest fires in Oregon, a result of hotter and drier temperatures.

The Battle of the Experts

In support of plaintiffs’ “source attribution” allegations and their claims concerning the U.S.’ contribution to climate change, Dr. James Hansen prepared a lengthy expert report and an accompanying co-authored paper on Assessing “Dangerous Climate Change”: Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature. Hansen cites research finding that the U.S. is an “unambiguous leader” in cumulative GHG emissions, having generated approximately 25% of emissions since 1751 (“more than double that of China, which falls second in the ranking”) and that the U.S. alone is responsible for a 0.15°C increase in global temperature, and discusses emission reduction targets for the U.S. based on a global climate budget. Dr. Hansen also discusses impacts such as sea level rise but does not explicitly quantify the proportional contribution of the United States to those impacts.

The question of the U.S. government’s responsibility for climate change is further explored in an expert report from Peter Erickson, a scientist at the Stockholm Environment Institute. He notes that the U.S. produces a substantial quantity of “territorial” emissions but that this is an incomplete indicator of responsibility for climate change. He calls for consideration of the United States’ consumption emissions, which are approximately 20% higher than territorial emissions in recent decades (due to the emissions from the production of goods imported into the U.S.), and notes that the country also bears some responsibility for emissions from the burning of fossil fuels produced in the United States. Erickson further notes that the U.S. has contributed to climate change by leasing and subsidizing the production of fossil fuels, but does not quantify the effect of those leases and subsidies on climate change (vis-à-vis global mean temperature change) or its impacts.

In response, the defendants’ experts argue that the plaintiffs’ experts fail to specify the degree to which U.S. government conduct was responsible for climate change or the plaintiffs’ alleged injuries; and fail to demonstrate that the U.S. government could provide adequate redress for the alleged injuries through policy and regulatory actions. In particular, the defendants’ experts state that the plaintiffs’ experts attributed increasingly frequent and severe water shortages, wildfires, droughts, and heat waves to U.S. government conduct without specifying the degree to which these events were caused or exacerbated by anthropogenic forcing on climate, let alone the specific contribution of the U.S. government. They also dispute the share of global emissions attributable to U.S. government action or inaction. One expert estimated that the U.S. government was responsible for no more than 4% of global emissions and that the other 96% of emissions were generated by: (i) countries other than the U.S., or (ii) fossil fuel consumption by entities other than the federal government that would have occurred regardless of federal policies and regulations. Another expert estimated that, even under a consumption-based accounting approach, the share of emissions attributable to the U.S. government was only 5 percent.

There is also a good deal in the plaintiffs’ expert reports that goes to proving impact attribution, and in some cases plaintiffs’ experts link observed impacts directly to a specific plaintiff’s alleged injuries. Plaintiffs’ experts draw relatively robust linkages between climate change and some alleged injuries based on downscaled climate impact data – for example, one expert presents data on historic and projected sea level rise in the town where one plaintiff lives,  and another discusses attribution studies linking specific extreme events that affected plaintiffs to anthropogenic climate change. In other instances, linkages are derived from qualitative inferences about how broader trends related to climate change have affected or will affect the plaintiffs. For example, with respect to a plaintiff who has had to move from her home in Cameron, Arizona because the springs her family depended on for water are drying up, one expert notes that the “pattern of drought in places like Arizona is directly linked to climate change.” Similarly, experts reporting on public health impacts note that the youth plaintiffs, like all children, are at a higher risk of certain health problems such as asthma due to climate change. In some cases, statements about impacts on plaintiffs are based on observed trends and impacts without reference to peer reviewed attribution studies that specifically examine the extent to which anthropogenic influence on climate is responsible for those observed trends and impacts. For example, one expert stated that snowpack had declined at ski resorts used by a plaintiff without citing research attributing the observed declines at those particular resorts to human activities (the assumption being that any change in snowpack is likely caused, at least in part, by the warming trends caused by rising greenhouse gas concentrations).

In response, the U.S. government’s experts argue that the plaintiffs’ experts failed to establish a conclusive link between anthropogenic climate change and the plaintiffs’ alleged injuries for two main reasons. First, the defense’s experts contend that the plaintiffs’ experts over-rely on inference, finding causal connections based on observations and general trends. For example, as plaintiffs point out in their Notice of Supplemental Disputed Facts, filed after the U.S. submitted its documents, one defense expert challenged the conclusions in an expert report on the psychiatric and medical consequences of climate change, asserting that the report “never directly links any of the consequences to any individual plaintiffs” and thus the impacts “remain theoretical possibilities, reported in various studies of natural disasters, but not conclusively identified in any of the Plaintiffs.” Second, the defense’s experts argue that the plaintiffs’ experts fail to account for other confounding factors that may have been responsible for the injuries, such as the effects of population growth and migration, forest and water management practices, and wildfire and flood protection practices on observed hydrological and ecological changes such as increases in wildfire severity and decreases in water supply.

What Next?

Ultimately, the district court found “that plaintiffs have provided sufficient evidence showing that causation for their claims is more than attenuated;” that “the ultimate issue of causation will require perhaps the most extensive evidence to determine at trial;” and that “[a] final ruling on this issue will benefit from a fully developed factual record where the Court can consider and weigh evidence from both parties.” But, even without the “trial of the century” moving forward we can see the contours of the “battle of experts” such a trial would entail. Plaintiffs’ primary goal with its expert testimony is to establish that the defendants are responsible for a meaningful contribution to climate change – an amount sufficient to prove causal relationships that satisfy the standing requirements and the even more demanding standards for showing a violation of public trust obligations and/or constitutional rights – and that climate change is the legal cause of specific injuries suffered by the plaintiffs. Defendants’ strategy is to undermine the reliability of plaintiffs’ proffers, and their tactic is to poke holes in plaintiffs’ expert reports by challenging the methodologies and results of plaintiffs’ source attribution studies, questioning the extent to which particular impacts have been (or can be) directly attributed to climate change, and highlighting the importance of confounding factors in creating any injuries suffered by the plaintiffs. We expect these lines of reasoning will predominate in this and other climate cases that seek to assign blame, force action, or recover damages for climate change.

For now, though, we expect to hear from the 9th Circuit on the validity of the constitutional and public trust claims. The courtroom battle over the science of climate change will have to wait for another day.

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