Tunnel vision

CARBON DIOXIDE is the main greenhouse gas emitted by human activities. But it is not the only gas capable of causing great harm to people and the planet. That point was driven home by the emissions scandal that engulfed Volkswagen last year. Since the 1990s policymakers in Europe had backed diesel as a way to reduce carbon emissions, turning a blind eye to other ways in which the fuel might damage human health. The VW affair drew back the veil on this trade-off. The company’s diesel engines did indeed deliver lower carbon emissions and better fuel economy, but at the cost of belching out noxious pollutants capable of shortening many lives.