By 1Sky blogger Nick Santos. See his bio at the end of this post.-- Luis
Take a good look at this graph from the Stern Review (data from McKinsey & Company). It's a graph of potential sources of CO2 reductions in Gigatons of CO2 equivalent per year (Abatement Gt CO2e/year) sorted by the cost of abatement in Euros per ton of CO2 equivalent reduced (Cost of abatement EUR/tCO2e). So, the height of a box shows the cost of that reduction, with negative costs being profits, and the width of the box shows the potential amount of CO2 we can reduce with it per year. The total area of a box is the total cost if we reduce the amount of CO2 in the box.