With a winter that brought snow to Tucson, Ariz., and 70-degree weather to New York City -- along with an Academy Award for the global-warming documentary "An Inconvenient Truth" -- climate change has become more ingrained in the public consciousness. Not everyone may be willing to overhaul their lives to accommodate the environment, but more people are opting for the rising number of options offered by companies to neutralize their "carbon footprints," meaning the amount of energy they consume. Most carbon-offset programs require consumers to make small payments that in turn go to programs that create renewable energy or absorb...