A leading environmentalist has claimed that
walking to the shops does more to cause global warming than driving; according to Chris Goodall, the author of
How to Live a Low-Carbon Life and a Green Party candidate in the UK, producing the food to provide a person with enough calories to walk to the shops is more energy-intensive than driving. Also, catching a diesel train is twice as polluting as driving a sports-utility vehicle over the same distance, paper bags are more environmentally damaging than plastic (because of the energy required to manufacture and transport them), organic milk causes more greenhouse emissions than intensively-produced non-organic milk, and while trees do absorb carbon, they produce methane, which is much more harmful.
So if you want to save the planet, forget about walking and drive everywhere like a mid-20th-century Los Angeleno, taking care to live a sedentary lifestyle in the interim. And don't even think about going to the gym; you'll go to green hell for such egregious wastes of carbon. Or perhaps not.
But does that take into account the food needed by the people that extract the ore from the ground, those that smelt it, those that turn it into a car, those that extract the petrol that makes the car go, those that are employed by car manufacturer to advertise said car, those that have car yard from which car was bought....and that's just the car.