Do you ever think about how your home and your lifestyle impacts the world at large? I cringe every time I commute to work (13 miles to work, 13 miles home), and dream of one day being able to bike. Your impact on the planet has come to be known as your "carbon footprint," and making your footprint as small as possible means understanding how your personal choices affect the planet.
To better understand your household's environmental impact, there are a plethora of calculators that let you enter in the specifics of your home, and car and airline travel habits to calculate your impact rating. Along with your rating they offer suggestions on how to lower your score, like switching to fluorescent light bulbs, installing skylights in low light areas, or simply recycling more.
This is my personal favorite: Low Impact Living's Environmental Impact Calculator. Designed well, easy to follow, and offering straight forward suggestions on how to lower your score, this calculator is a great place to start exploring your impact.
Here are some other calculators that offer help: