# Global photosynthetic efficiency

Value 0.2 % Biosphere Barber J. Biological solar energy. Philos Transact A Math Phys Eng Sci. 2007 Apr 15 365(1853):1007-23. p.1010 4th paragraphPubMed ID17272238 "On a global basis, the efficiency of photosynthesis is significantly lower than for optimal agricultural crops (1%-2%) owing to seasonal changes and the existence of large areas of land on our planet, which do not sustain vegetation. Thus, the rate of energy stored annually by photosynthesis, estimated to be 100 TW, represents just 0.1% conversion, given that over the same time period, solar energy incident on our planet averages at a rate of 100 000 TW (for value of 175000 TW see BNID 100943). A similar amount of photosynthetic activity occurs in the oceans, but most of the fixed carbon is rapidly recycled into the food chain (Falkowsky & Raven 1997). Therefore, overall, an approximate efficiency of global photosynthesis is 0.2%." Another way to calculate is by the ratio between energy stored by net primary productivity and energy from annual solar flux: Annual Solar power arriving to earth 175 peta watt (BNID 100943) 175×10^15[J/sec/m^2]×3600[sec/hour]×24[hours/day]×365[days/yr]=5.5188×10^21 kJ/yr. Energy stored per carbon (in carbohydrate) in photosynthesis 39 kJ/g carbon (BNID 100810). Global Net Primary Productivity 105 peta g/yr (BNID 102933) 105×10^15 [peta g C/yr] ×39 [kJ/g C]=4.095×10^18 kJ/yr. Global photosynthetic efficiency=4.095×10^18 [kJ/yr]/ 5.5188×10^21 [kJ/yr]=7.4×10^-4˜0.1% (http://www.feem-web.it/potsdam/files/schellnhuber_ppt1.pdf use this method with slightly different figures, and arrive at efficiency of 0.15%) Ron Milo - Admin 100761