Green Mountain Chrysler Plymouth Dodge Jeep v. Crombie

A number of automobile manufacturers and dealers, including Green Mountain Chrysler Plymouth Dodge Jeep (the manufacturers) (plaintiffs), challenged a Vermont state law restricting vehicle greenhouse-gas emissions. To substantiate Vermont’s strong regulatory interest in mitigating the adverse effects of climate change, the state employed expert testimony by Dr. James Hansen. Hansen testified about the likely extinction of species and the regional impacts of global warming and offered predictions regarding ice-sheet melting leading to sea level rise. He also posited the idea of a tipping point, past which the effects of climate change would increase dramatically. Hansen cited substantial data in support of these theories and relied on his expertise to make predictions about sea-level rise. Hansen acknowledged that exact predictions about sea-level rise were not possible. The manufacturers offered no evidence contradicting Hansen’s testimony regarding species extinction or the regional impacts of global warming. The manufacturers did bring a rebuttal witness, Dr. John Christy, who testified that Hansen’s testimony regarding sea-level rise was not supported by scientific evidence and that the satellite data relied on by Hansen consisted of only a few years of data. The manufacturers contended that the absence of objective evidence and controlled testing for Hansen’s theories rendered Hansen’s testimony insufficiently unreliable to be admissible as expert testimony and moved to have the testimony excluded.