There are many reasons to take up commuting by bicycle. With all the furor over global warming is spurred a lot of those on the left side of the political spectrum to call for the "Greening" of America. I am not one of these. On the continuum of political ideologies I tend to be conservative; however, I am literally an old-school conservative which means I tend to want to conserve things.
I have many reasons for taking up bicycle commuting from a belief standpoint, economic, and health reasons. From a belief standpoint I believe that mankind has a moral duty to be a conservator of the earth and for over 200 hundred years mankind has been consuming fossil fuels like a drunk sailor drinking cheap beer at a waterfront bar. Humankind has been dipping deeply into a limited energy supply without considering the impact on future generations. Before we get too deeply into this I don't buy the whole theory of global warming mainly because I understand what sort of "camel" the loony left is really trying to bring in under the tent.
When politicians like Al Gore sit there and preach at the American public to use less energy while he himself is living in a mansion that uses more electricity in one month than one average person does a year and he sets himself up a for-profit company selling "carbon credits" it's pretty evident to me that reversing global warming is not his real agenda. His real agenda is to have everyone else cut back their use while he and the other "privileged few" continue business as usual. What is really at issue is the development and emergence of an oligarchical one world government. A socialist regime where matters like the environment and wealth distribution is dictated by the privileged few.
The evidence for global warming is rather inconclusive in my opinion; however, I do believe to some extent that what we are doing with the consumption of fossil fuels and the forests of the world is not helping the situation. Nature tends to try to stay in balance and all that released carbon has to go someplace even if it is sinking to the bottom of the oceans and such an overload has to have some sort impact.
From a health standpoint I cycle because when I primarily use my own muscles for propulsion I burn on the average of 1700 calories which I do not do when driving. The human body is an organic machine that is designed to do work. In the time before civilization that work was hunting and gathering then later agriculture. These are activities that consume massive amounts of energy that now because of industrialization our bodies no longer are used to their full potential; however, we continue to feed ourselves with foods of higher caloric content. What is the impact of this? Well, we're seeing obesity at record levels as well as greater incidence of type II diabetes. Since I started commuting I found myself sleeping deeper and better on days when I left the car behind. My metabolism is also much improved. I have considerably less worry of weight gain when on a given day I am riding over 31 miles and I've scrubbed off over 1000 calories or more. I also have a considerably improved outlook on life in general from being out in the sunlight for over two hours every day.