# Human Appropriation of Net Primary Production: From a Planet to a Pixel
## 2 Background and Literature Review
### HANPP as a Modernized Ecological Footprint  
A more precise and broadly useful approach to measuring ecological footprint is offered by the Human Appropriation of Net Primary Production (HANPP). HANPP is defined by [PERSON] et al. (2007) [6] as the difference between potential net primary production (NPP) and the NPP remaining post-harvest. This is the NPP made unavailable to ecosystems by human use of land. By using this externally consistent approach, the problem of \"generic\" land inherent in the ecological footprint concept is solved on two fronts. First, enormous variations in the ecological productivity of land, which range from 0 to about 1500 gCm\({}^{-2}\)yr\({}^{-1}\)[7; 8], are incorporated into the analysis. Second, the varying degrees to which this productivity is appropriated or colonized by human use are measured, whether by changing the ecological productivity of the land (HANPP-land use) or by harvesting it (HANPP-harvest). In this manner, it is not the land area of the Earth that constrains human carrying capacity, but the Earth's terrestrial ecological productivity. Rather than geographical space, the human ecological niche is compared to photosynthetic capacity that can be measured at scales from the planet to a 30 m pixel, as explored below. Third, HANPP is also identifiable to specific plots of land, thus enabling spatially-specific and geospatial analysis. Critically, by tracing HANPP (harvest) in the form of biomass products such as food or lumber, from the point of production to the point of consumption, a spatially-specific ecological footprint can also be developed on the basis of the consumption of biomass products at specific times and places (this is termed embodied HANPP) [9]. Fourth, HANPP is quantifiable in relation to carrying capacity limitations--among which NPP is perhaps the most critical (Running 2012)--and a safe operating space within those limits [10]. For HANPP, the local safe operating space can be defined as a maximum percentage of NPP, or as a minimum NPP remaining post-harvest--termed NPP (ecological). Moreover, a focus on HANPP as the core of an ecological footprint takes into account the dominant effect HANPP has, through photosynthesis, on water [11], nitrogen [12] and phosphorus [13] use, the profound effect land use and habitat change have on biodiversity loss [14], and the substantial effect, both positive and negative, land use has on atmosphericcarbon through Forestry and Other Land Use (FOLU) [15]. HANPP is often measured in terms of dry organic matter but can be easily converted to carbon simply by taking the carbon content of plant biomass--usually 45% [7], or sometimes 47% [16], though there is some variation in individual plants and species [8]. This enables HANPP to be related to carbon footprint, such as the land use component of net carbon emissions. Fourth, carbon can be readily converted to an energy measure, (e.g., 1 g C = 32,800 joules) so that energy-based comparisons can be drawn. For example, the energy content of global gross terrestrial primary production (GPP) of about 110-120 PgCyr\({}^{-1}\) is about 37-39 \(\times\) 10\({}^{20}\) joules, and NPP, using the 56.8 PgCyr\({}^{-1}\) estimate, is 18.6 \(\times\) 10\({}^{20}\) joules--0.15 percent of the 37,693 \(\times\) 10\({}^{20}\) joules yr\({}^{-1}\) of radiant solar energy reaching Earth. In comparison, global commercial energy consumption is about 6-7 \(\times\) 10\({}^{20}\) joules yr\({}^{-1}\) and rising (International Energy Administration 2020). In fact, HANPP is an energy-based concept at its heart, and this enables analyses founded in energy accounting, such as energy return on investment (EROI). Fifth and finally, like other footprints that have withstood the test of scientific critique, such as water and carbon footprints, HANPP is closely tied to fundamental, measurable earth system processes.