$2.$ As law students all dutifully learn in their first year Torts class, a prima facie negligence claim must satisfy four elements$-$duty, breach, causation, and injury. None of these elements is easy to establish in a climate lawsuit. In terms of causation, for example, how can plaintiffs persuasively link the particular emissions of cars driven in California with reduced snowpack in the Sierra Nevada? And even if a causal link can be established between the offending action and the harm, what is the proper measure of the car companies liability in the face of multiple sources of greenhouse gases over an extended time period?