Transcripts of imhoff_carbon_currency In this study we looked at two factors. We looked at NPP which is basically the amount of plant material generated on an annual basis on the land surface and the HANPP, which is the amount of plant material that people require to generate the end products of food and fiber and building materials also on an annual basis. The interesting thing about looking at NPP or net primary production is that you can also look at it in terms of carbon. Because photosynthesis is basically the process where carbon dioxide is taken out of the atmosphere and fixed in plant material. So we look at NPP as sort of the common currency for looking at climate change, carbon assessment, and food secuirty and socio ecological issues.