The limits to complexity: A thermodynamic history of bioenergy

sThe history of civilization is biased toward the use of bioenergy because of the biophysics of life and the structure of our natural environment. Energy physically drives the creation and maintenance of complex systems, which is shown here from simple molecular structures to empires. Only a fraction of the complexity currently supported by fossil fuels can be maintained using the energy in plant biomass alone, which is limited by global net primary productivity. From the dawn of civilization, agricultural land has always been used for energy for transportation, via feed for animals, and there has always been a trade-off between food, fuel, and environment'. The United States (USA), Germany, and Brazil now use roughly 12% of agricultural land for biofuels, but energy efficiency improvements by 2050 could require only 11% of US agricultural land or 15% of forest land for biofuels to support all modes of US transportation. Despite its limitations, bioenergy has been extensively used for thousands of years and probability theory suggests it will continue to be a critical energy resource. (c) 2013 Society of Chemical Industry and John Wiley & Sons, Ltd