So let's say little Timmy rides his bike around town, and is committed to preserving the environment so he uses as little carbon as possible. There is a power station next to him that burns massive amounts of fossil fuel, and is responsible for 99.9% of the social cost involved. Naturally since the usage of some degree of carbon is inevitable, Timmy bears a small 0.01% of it. The government decides to pass a carbon tax, so they take the sum of social costs and divide it by two. If social costs were say, $5 billion, Timmy is then responsible for $5 billion/2 x GHG emissions. Thus a significant portion of the costs of carbon pollution by the power station is put onto Timmy, despite his best effort to be environmentally-conscious (and should not be penalized). The power station's taxes are lower (because parts of the burden is transferred to Timmy) than the profit gained from the current level of emission, so does not decrease emissions as much as he should based on the tax. The next year, social costs are still there and not fully taxed away - an inefficient system. Now Timmy grows up and gets a car. He really likes strawberries but the nearest field is an hour away, so he is now faced with the economic dilemma of minimizing his carbon emissions (as it requires driving) and maximizing consumption (as he really likes strawberries). Should he do it? The benefit-cost analysis really depends on a ton of factors specific to the situation, i.e. how far it is, current gas prices, etc.