The way I see it, small changes multiplied by a huge population gives a huge economy of scale. For example, one can calculate, for example, the amount of energy saved in BTU if everyone lowered their thermostat in the winter by 2 deg F, or, conversely, raised it in the summer by 2 degrees. Market pressures like peak vs. off-peak pricing for electricity can modify behavior. One can drive a higher-milage internal combustion car. There always is a cost to any human activity; Niven called it the TaNSTAAFL principle ("There ain't no such thing as a free lunch!")

What Blue Frog did was a type of cradle-to-grave analysis. These are two-edged tools. You need a lot of information to do these, and can get discouraged if you don't know all the inputs and outputs. Bottom line: do the best you can. I personally like the idea of planting more trees and having gardens on roofs. The tree is one of the most efficient CO2 sinks there is!