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Because carbon calculators ask for only ­rough estimates, it's fairly easy for investigators to approximate the footprints of celebrities and politicians. Analysts hoping to uncover hypocrisy target high-profile figures, especially those who promote environmentalism. Although Live Earth performer Madonna and other celebrities like Tom Cruise and David Beckham have been accused of flying frequently, sometimes with large entourages,­ former Vice President Al Gore has drawn the harshest accusations. His popular movie "An Inconvenient Truth" raised awareness of carbon reductions but also stirred an independent firm to look into his utility records. The Gores' spokesperson did not deny the $30,000 per year in utility bills but emphasized that the couple subscribes to green power, plans on installing solar panels and purchases offsets [source: ABC News].

Reducing Carbon Footprints

Carbon footprints help people keep track of changes. Because footprints quantify an amount of carbon that increases or decreases based on energy use, they let people know that a new hybrid car or home insulation really does help lower emissions.

­­Transportation accounts for 33 percent of CO2 emissions in the United States, so many people try to lower their mileage [source: EIA]. Some walk or bike whenever possible; others carpool, take public transport or invest in fuel-efficient cars.

Home energy use accounts for 21 percent of U.S. CO2 emissions, so it helps to have an efficient home. [source: EIA] Setting the thermostat at a moderate temperature and installing good insulation and double-paned windows lowers energy costs while keeping your house comfortable. Compact fluorescent lamps (CFLs), energy-efficient appliances and green power sources also help lower consumption.

Of course, individual efforts to reduce emissions can go only so far. Cutting CO2 and other greenhouse gases down to safer levels requires significant government regulation. Lessening carbon footprints does, however, let people see where they are and how they can change. Those who think government regulation moves too slowly or who want to accept personal responsibility for their emissions can track their own reductions and alter their individual habits.

To learn more about carbon footprints, global warming and other related topics, please check out the links on the next page.