Tesla's electric trucks are great but they won't save the planet

Electric cars used to be a joke – the ugly, expensive option for wealthy tree-huggers. But thanks to companies like Tesla, they are now sleek, desirable and increasingly affordable.

With the car revolution already under way, Tesla and other manufacturers are turning their attention to heavier vehicles. Yesterday, Tesla CEO Elon Musk unveiled his all-electric truck, the Tesla Semi, in a showy event attended by hundreds of guests.

Just a few years ago it seemed unlikely that diesel’s dominance in heavy vehicles could ever be challenged. Now the question is how long the…