Climate change, if left unchecked, threatens to undermine the last half century of gains in global health. That's the conclusion of a study released Monday by an international commission convened by the Lancet, a prestigious medical journal based in the UK. Declaring it a "medical emergency," the authors argued that the potential impacts of global warming—such as floods, drought, heat stress, catastrophic storms, the spread of disease, and increased food insecurity—pose a "potentially catastrophic risk" to human health. The study's authors, however, highlight a potential sliver of good news: Tackling the issue immediately presents "the greatest global health opportunity of...