Which is more polluting—driving a mile to work or walking that mile? The easy answer is, of course, driving. Cars have tailpipes; people don't. Far more energy is needed to push a 3,000-pound car along the road than is needed to move a 150- to 250-pound body along a sidewalk. Walking seems like the green thing to do.
But appearances can be deceiving, making easy answers dead wrong. That's the case here when the calories expended in walking are replaced.
Counting the Ways Energy Is Consumed in the Food-Supply Chain
The primary reason that walking to work can be more polluting than driving is that growing crops and raising animals so that they can be consumed and digested by humans involves a food-supply chain that now extends to all corners of the Earth and uses a lot of energy. An unavoidable byproduct of this energy use is greenhouse gas emissions.
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Concluding Comment
When it comes to energy use and greenhouse gases emitted, appearances can be grossly deceiving. Granted, people who drive everywhere are energy users and polluters. But walkers also use fossil fuels through the food they eat to replace the calories burned while walking. Of course, driving can be more polluting under some circumstances, such as when large SUVs are the preferred vehicles or when drivers insist on doing wheelies at every stoplight. Bicycling the distance can also be less polluting than driving. Dunn-Rankin sums up the central, largely counterintuitive, point of this commentary: "Driving a small [or moderate-size] car and not having to replace burned calories saves more energy (and greenhouse gases) than walking when the extra calories expended are replaced."
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