In 1987, the state of Texas convicted Steven Mark Chaney for a murder he did not commit. Chaney was convicted largely based on “bite mark” evidence. Over 25 years later, Texas passed a “junk science law,” allowing people like Chaney to seek release if their convictions were based on questionable science. Chris Fabricant, an attorney with the Innocence Project, made it his mission to exonerate those who lost their freedom due to pseudo-scientific evidence and eradicate flawed forensics from criminal cases. More than three decades into his imprisonment, the Texas Court of Criminal Appeals found Chaney innocent. Just as criminal defense lawyers work to expunge questionable scientific evidence in cases where fundamental freedoms are at stake, so too should climate litigators.
Questionable “science” has long contaminated legal processes and gravely harmed the innocent—sometimes because it reflects a well-intentioned but inaccurate state of scientific understanding and sometimes because profits and politics have intervened. The climate crisis is the latest—and arguably, most consequential—target of the science wars. It’s not just climate deniers offering up misinformation; it’s global leaders, the media, the United Nations, and sometimes even human rights lawyers. We ask, “Do lawyers have an obligation to present the best available scientific evidence to courts in climate cases?” The answer is unequivocally yes.
A graphic published by the UNFCCC implies that humanity will be safe at 1.5°C of warming above pre-industrial levels. Yet, today—at 1.1°C to 1.3°C—climate-powered extreme events already devastate lives across the globe.
In 2011, the UN Framework Convention on Climate Change acknowledged the importance of grounding climate action in the “best available scientific knowledge.” The Paris Agreement and Glasgow Climate Pact echo this call. Yet, too many global leaders remain committed to holding heating to the policy—not scientific—targets of 1.5°C to 2.0°C over pre-industrial levels. According to scientists working with the Intergovernmental Panel on Climate Change—a hybrid organization straddling the climate science–climate policy debate—the 2°C target is a “compromise between what is deemed possible” and what is deemed “desirable,” rather than a “‘planetary boundary’ that . . . separates a ‘safe’ from a ‘dangerous’ world.” Scientists and scholars underscore that a threshold of 1.5°C is more political than pragmatic and that hitting that mark would be catastrophic. Others warn that 1.5°C propels us toward “climate tipping points” where change is irreversible. Despite these warnings, backed by decades of evidence, lawyers continue to mistakenly assert to courts that 1.5°C will protect human well-being and, thus, human rights. Given the dire implications of relying on flawed targets in the climate context, it is crucial that lawyers rethink the call to embed 1.5°C into jurisprudence. Below, we briefly discuss the challenges to ensuring the best science comes into courts and then what compels lawyers to ensure that it does.
Presumption of admissibility
Evidentiary standards are designed to ensure the overall quality of information presented in legal processes. Some of these standards are aimed at establishing who can serve as a court expert when judges cannot form an opinion on their own because specialized knowledge is needed. As one judge explained, “[T]he role of the expert is not simply to arrive at a conclusion but to expose criteria which will enable that conclusion to be evaluated,” empowering the judge to effectuate justice.
A notable gap in the law is that few—if any—courts concretely define and set out criteria for “best available scientific evidence.” Further, international admissibility rules often include a presumption of admissibility. Consequently, lawyers can—and do—readily classify anything resembling climate science as the “best available science.” Allowing a large spectrum of scientific information as “best” leaves significant scope to admit poor-quality, politically motivated information into judicial processes. The risk is especially high when divisive rhetoric or significant financial considerations are at play, as is often the case with climate litigation.
Given this risk, we turn to the gatekeeping function provided by court-articulated criteria, legal ethics, and the right to science.
Standards of evidence
While courts have failed to define “best available science,” they have established principles for expert testimony. In 1975, the US Congress passed Federal Rule 702 to guide the admissibility of expert evidence in federal courts. In 1994, the US Supreme Court interpreted this rule in Daubert v. Merrell Dow Pharmaceuticals, creating the “Daubert Standard.” Today, jurisdictions around the world follow a form of Daubert, according to which the judge assesses whether evidence is based on scientifically valid reasoning and whether it has been properly applied to the facts at issue. If the answer is no, the testimony is excluded.
Daubert includes five non-exclusive, non-binding factors for judges to consider: 1) whether the technique or theory can be or has been tested; 2) whether it has been subjected to peer review and publication; 3) the known or potential error rate; 4) the existence and maintenance of standards controlling its operation; and 5) whether it has attracted widespread acceptance within a relevant scientific community.
These factors are meant not only to operate as quality control but to align with criteria often used to define the best available science—the most up-to-date information that 1) derives from internationally recognized scientific practices, methodologies, and standards; 2) maximizes quality and objectivity; 3) is publicly released and published through a peer-review process; 4) clearly communicates risks and uncertainties; and 5) reflects a consensus (where consensus exists) or at least rests on good-faith peer-reviewed studies from multiple research groups.
Although courts do not mandate that scientific evidence satisfy these criteria, we argue that human rights practitioners are ethically obligated to ensure the quality of the evidence they present.
Legal systems everywhere possess ethical standards for lawyers. In the United States, lawyers have a “duty of candor” toward courts, which includes refraining from offering evidence “that the lawyer knows to be false.” If a lawyer offers false evidence, they must take “reasonable remedial measures” to disclose the error or withdraw the evidence. Lawyers are also obligated to promote confidence in the rule of law and legal systems. Ensuring that only quality science is presented in court is an important way to uphold that duty.
In Europe and Latin America, lawyers are barred from knowingly giving false or misleading information to courts. Similarly, the International Bar Association’s code of ethics requires that “lawyers shall never knowingly give to the court incorrect information.”
Lawyers may argue they are not providing the misleading climate targets cited by the expert witnesses they deploy or the political representatives who negotiated the Paris Agreement Nevertheless, lawyers hold a duty to refrain from submitting compromised, outdated, or otherwise dangerous scientific evidence.
The human right to (good) science
Finally, Article 15 of the International Covenant on Economic, Social and Cultural Rights recognizes a human right to science. According to organizations like the American Association for the Advancement of Science and its Center for Responsibility and Justice, states must recognize the right of everyone to “enjoy the benefits of scientific progress.” Employing anything other than the best available science arguably deprives people of this right.
Just as flawed evidence stripped Steven Chancy of his fundamental right of freedom for over 30 years, reaching and remaining at 1.5°C will similarly deprive billions of their most basic human rights. Perhaps there was a time when the legal community could plausibly say, “We did not know.” That is no longer the case. The science is clear: 1.5°C is not only flawed but dangerous. Our aim must be to remove this unsafe target from the evidentiary foundations of climate cases everywhere. To do otherwise would erode trust in both science and law, undermine justice, and further endanger humanity.
With thanks to Anthony Ghaly, Maggie Andresen, and this essay’s editors for their assistance.