| Method |
Seventeen global models of terrestrial biogeochemistry were compared with respect to annual and seasonal fluxes of net primary productivity (NPP) for the land biosphere. The comparison, sponsored by IGBP-GAIM/DIS/GCTE, used standardized input variables wherever possible and was carried out through two international workshops and over the internet. The models differed widely in complexity and original purpose, but could be grouped in three major categories: satellite-based models that use data from the NOAA/AVHRR sensor as their major input stream (CASA, GLO-PEM, SDBM, PLAI 0.1, SILVAN 2.2, and TEM 4.0), and models that simulate both vegetation structure and carbon fluxes (BIOME3, DOLY and HYBRID 3.0). The simulations resulted in a range of total NPP values (44.4-66.3 Pg C/Yr), after removal of two outliers (which produced extreme results as artefacts due to the comparison). Note that value above includes the two outliers, 80.5 Pg C/Yr (TURC), and 39.9 Pg C/Yr (HYBRID) |