eldavojohn writes "CNN is running an article on a new angle of attack to reducing greenhouse gases. After meeting with the US Department of Energy on the concept, the researchers revealed the details that each 'tree' (really a small building structure in the concept design) would cost about as much as a Toyota and remove 1 ton of CO2 from the air per day. Don't worry, they're accounting for the energy the 'tree' uses to operate: 'By the time we make liquid C02 we have spent approximately 50 kilojoules [of electricity] per mole of C02. Compare that to the average power plant in the US, which produces one mole of C02 with every 230 kilojoules of electricity. In other words, if we simply plugged our device in to the power grid to satisfy its energy needs, for every roughly 1,000 kilograms [of carbon dioxide] we collected we would re-emit 200, so 800 we can chalk up as having been successful.' Each unit would remove 20 automobiles' worth of CO2 from the air and cost about as much as a Toyota... so the plan might be a five percent surcharge on automobiles to fund these synthetic tree farms."