Buried sunshine

In this reference article, Jeffrey S Dukes calculates that the amount of fossil fuel consumed in 1998 required 44 Eg Carbon as precursor material (1 Eg = 1 Exagram = 10E18 g or a 1000 billion tonne), i.e. over 400 times the earth's net primary productivity (NPP). A conservative estimate is that it would require 22% of terrestrial NPP to replace fossil fuel consumption with modern biomass. Such a large-scale use of biomass for energy would have a dramatic impact though on other species. The difference between 22% and 400 times (40,000%) can be explained by the recovery factor of photosynthetically fixed carbon into fossil fuels. This process is less than 10% efficient in case of coal, while less than 0.01% of photosynthetic carbon ends up in oil or gas.