Oil companies have started to hint in their advertising that easy oil will not last forever. Still, I was a little surprised to find that BP’s site has a cheeky little Flash-based household carbon emissions calculator (complete with animated Fisher-Price men), advertised online with a tagline of “Small carbon footprints can make a big difference.”Since the calculator updates the totals dynamically, you can very easily see how certain steps, like going car-free, will very substantially cut your household carbon emissions — the gases that cause global warming. Example: a hobo living in a sedan and driving 20,000 miles a year (still fewer miles than the average American car is driven) produces more carbon dioxide than my entire household, even with my frequent-flyer habit.

The Chicago-based Center for Neighborhood Technology runs two more-detailed air pollution calculators: one measures carbon emissions from personal transportation and the other measures toxic air pollution generated by all household activities.