18 - Determining Present Patterns of Global Productivity

Abstract

Net primary productivity (NPP), the flux of carbon between atmosphere and vegetation, is a key quantity of the global carbon cycle, and hence, highly relevant to the assessment of impacts from and feedbacks to climatic change. The balance between atmospheric concentrations of carbon dioxide, and storage of carbon on land and in the oceans is directly affected by changes that may occur in net ecosystem productivity (NEP), which, in turn, is the difference between total annual NPP and heterotrophic respiration. NPP is a key ecosystem variable, yet no agreed methodology presently exists for extrapolating sparse and sometimes uncertain field observations of NPP to produce a consistent database representative of major worldwide vegetation and environmental regimes. This chapter examines the auspices of the Global Primary Production Data Initiative, and a number of collaborating research groups making progress in compiling field-site measurements of NPP and associated environmental data, agreeing on consistent standards for cross-site comparisons and scaling up from point measurements to grid cells, and investigating new ways to relate NPP observations to other data sources, such as satellite data. A consistent data set exists that will soon become the de facto standard for twentieth century NPP observations. Data from experiments and global observing systems forms the foundation for a higher level of confidence in assessments of future NPP, and hence, the overall carbon balance. Without such a capacity, Earth system science will be inhibited to provide input into a policy-making progress, which is, for the first time in history, seriously considering the global nature of the human environment.