Global human appropriation of net primary production doubled in the 20th century

Abstract

Global increases in population, consumption, and gross domestic product raise concerns about the sustainability of the current and future use of natural resources. The human appropriation of net primary production (HANPP) provides a useful measure of human intervention into the biosphere. The productive capacity of land is appropriated by harvesting or burning biomass and by converting natural ecosystems to managed lands with lower productivity. This work analyzes trends in HANPP from 1910 to 2005 and finds that although human population has grown fourfold and economic output 17-fold, global HANPP has only doubled. Despite this increase in efficiency, HANPP has still risen from 6.9 Gt of carbon per y in 1910 to 14.8 GtC/y in 2005, i.e., from 13% to 25% of the net primary production of potential vegetation. Biomass harvested per capita and year has slightly declined despite growth in consumption because of a decline in reliance on bioenergy and higher conversion efficiencies of primary biomass to products. The rise in efficiency is overwhelmingly due to increased crop yields, albeit frequently associated with substantial ecological costs, such as fossil energy inputs, soil degradation, and biodiversity loss. If humans can maintain the past trend lines in efficiency gains, we estimate that HANPP might only grow to 27-29% by 2050, but providing large amounts of bioenergy could increase global HANPP to 44%. This result calls for caution in refocusing the energy economy on land-based resources and for strategies that foster the continuation of increases in land-use efficiency without excessively increasing ecological costs of intensification.

Keywords: agriculture; food; global carbon cycle; land use intensity; resource use.

Fig. 1.

Global HANPP throughout the last century. (A) Development of global HANPP by major land use type and human induced fires from 1910 to 2005. (B) Sensitivity of global HANPP trends to data uncertainty and different model assumptions. The standard estimate of HANPP (black line) is compared with a low and a high estimate and to an estimate excluding changes in NPP_pot due to CO₂ fertilization (constant NPP_pot of 1990). HANPP is measured in GtC/y (1 Gt = 1 Pg = 10¹⁵ g or 10⁹ t). See SI Appendix for details. (C) Biomass harvest (HANPP_harv) and final consumption of biomass products (plant and animal based food, food, timber, fuel wood, and other industrial biomass use; tC/cap per y) grew largely in parallel with population. (D) HANPP intensity measured as HANPP per capita (tC/cap per y), HANPP per unit of GDP (kgC/1990 constant international dollars $ per y) and total HANPP per unit of biomass harvest (HANPP_harv) (gC/gC) declined, indicating increasing land use efficiency.

Fig. 2.

HANPP on global croplands. Development of harvested NPP (HANPP_harv) and productivity losses due to land change (HANPP_luc) compared with potential NPP (NPP_pot) and NPP remaining in ecosystems after harvest (NPP_eco). Absolute values (GtC/y) in A; per unit of cropped area (gC/m² per y) in B.

Fig. 3.

Development of HANPP and HANPP per capita from 1910 to 2005 in five world regions. HANPP (percent) measures HANPP as a percentage of the NPP of the potential vegetation, i.e., the vegetation assumed to exist in the absence of land use. Asia*, Asia excluding those countries which are part of the FSU-EE Region; FSU-EE, Former Soviet Union and Eastern Europe. See SI Appendix for definition of regions.

Fig. 4.

Scenarios for the development on HANPP until 2050. Whereas scenarios A–C assume a continuation of past trends, scenarios D and E add additional primary biomass harvest to scenario B (see text and SI Appendix for details). Based on upper and lower boundary values for deployment levels of biomass for energy, we assumed an additional harvest for energy production of 50 EJ/y (scenario D) and 250 EJ/y (scenario E) over the present value. Continuation of past trends would result in moderate growth of HANPP until 2050. Increasing the production of bioenergy, however, could dramatically increase global HANPP (scenario E).