Smokers are deterred by the warning labels on cigarette packages about health risks. Would warning labels about the effects of airline flights on global warming be as effective? The Institute of Public Policy Research thinks so. In a report, it recommends giving per person emissions data about flights to passengers, along with comparisons of energy consumption for similar trips on alternative transportation, like trains. Given that trains are, in general, more environmentally friendly than airplanes, it’s unlikely that any of the major carriers will want to advertise for their competition, but simple warning labels about airline energy usage might be feasible.