An ecosystem can't be truly healthy if its inhabitants are sick. And with heart disease, stroke, obesity and diabetes hitting record highs around the world, the planet finds itself supporting an increasingly ailing human population.
The thing about these particular health conditions is that they're often lifestyle-related, connected to poor eating habits and a lack of exercise. If it's true, as the World Health Organization reports, that heart disease and stroke are the leading cause of death worldwide and obesity (which is tied to diabetes type 2) is a global epidemic, then getting more exercise could conceivably make a real difference in global health levels [source: WHO].
Since so many working adults don't have time to fit in their recommended daily exercise, turning exercise into a crucial, unavoidable part of the daily routine -- like getting to work or to the grocery store -- is an ideal way to increase activity levels. Since cycling is an aerobic activity, it not only strengthens the body and lowers "bad cholesterol" and raises "good" cholesterol levels, but it also burns a lot of calories, contributing to healthy-weight maintenance, which could make a substantial dent in the number of Earth's inhabitants with type 2 diabetes.
And with all that extra money that would have gone into caring for sick people, the world could increase its spending on things like solar and wind power and outfitting factories with the latest emissions-control equipment.
And speaking of air pollution …