23 - Estimations of Global Terrestrial Productivity: Converging toward a Single Number?

Abstract

Terrestrial ecosystems significantly contribute to the global carbon cycle. The chapter discusses that stocks and fluxes are increasingly altered by human activities, through changes in land use, in atmospheric composition, and in climate. This carbon sink results from an increase in global terrestrial net primary productivity (NPP). Thus, it is essential to know what the present value of global NPP is, and whether it will continue to increase to sustain an important terrestrial carbon sink. This chapter uses recent information provided in each of the biome-updated estimates of global values for NPP and phytomass. Finally, the current and expected changes in global NPP and net ecosystem productivity are discussed. The main source of uncertainty on global NPP lies in the biome area, and especially in forest area. Significant progress on biome maps is expected in the near future from the use of satellite data, once the classification done using such data can be given biome names that can receive a large acceptance. There is also some uncertainty on the current and future rates of change in NPP. Research on this aspect, at all scales, is developing fast. The chapter emphasizes on predicting more precisely the impact of human activities on NPP and on the carbon cycle in general. This information is crucial to design and implement sustainable development of human societies.