Environmental litigation, particularly toxic tort litigation, inevitably turns on scientific evidence about causation.  Beginning with the Supreme Court’s Daubert decision in 1993, trial courts have repeatedly been admonished to take seriously their role as gatekeepers who are required to keep from juries and other fact-finders ”junk science” and other expert evidence that is not sufficiently reliable to be considered.

Although no one would disagree that one key responsibility of any judge is to protect against the admission of unreliable evidence,  a recent unpublished decision by the Ninth Circuit in Whitlock v. Pepsi Americas suggests the dilemma of trial courts in attempting to execute that responsibility in environmental cases.  There, the trial judge had granted summary judgment dismissing a toxic tort action which was based on what the judge found to be unreliable scientific evidence of causation.  For example, one of the plaintiffs’ experts relied upon occupational studies to buttress his causation opinion even though the exposure levels examined in the studies were considerably higher  than the ones to which plaintiffs had been exposed.  The Ninth Circuit, however, reversed, quoting an earlier 2010 decision by that court that held that “Shaky but admissible evidence is to be attacked by cross examination, contrary evidence, and attention to the burden of proof, not exclusion.”

The difference between “shaky but admissible” and unreliable and inadmissible evidence would seem to be entirely in the eye of the beholder.   As long as appellate courts, like the Ninth Circuit in Whitlock, are willing to second-guess Daubert decisions in close cases, we should not be surprised if trial courts do not want to take the risk that they will be reversed if they exclude scientific evidence.