They're absolutely more efficient cars (relative to petrol), and arguably still the more "eco-friendly" - but that's not a well-defined term. They exhaust high

They're absolutely more efficient cars (relative to petrol), and arguably still the more "eco-friendly" - but that's not a well-defined term. They exhaust high amounts of nitrous oxides (high-temperature lean combustion - same thing that makes them efficient!), and particulates (hard to evaporate and burn the fuel in the few milliseconds where power is made), which are bad for anything living by a major road, but don't hang around in the atmosphere for more than a few weeks. I've seen limited evidence of regional effects, but certainly not the global, centuries-long effects of CO2.