Scientific challenges for anthropogenic research in the 21st century: Problems of scale

Abstract

Research into the behaviour of the earth system in the recent past, the current era and the near future, a period that nowadays is recognised as the Anthropocene (Crutzen 2002), requires an adequate description of the dynamics of many different components and their interactions. Major components are the atmosphere, the biosphere (including humans and their societies) and the oceans. The dynamics of all these components are nowadays influenced by human activities. The natural components and the anthropogenic components of the earth system should be studied in an integrated way. In this chapter I will provide ways to actually link the natural or environmental and anthropogenic dimensions. Most components function on many different scales and levels: from molecules or other particles to the whole atmosphere, from individuals to nations, from chlorophyll grains to whole plants, from plants to ecosystems, from landscapes to biomes, from streams to watersheds to the full hydrological cycle, etc. Many processes determine the specific behaviour of each component. These processes determine linkages and interactions at different scales and levels between different components. Such complexity should be represented in global change research because one can rarely describe complex behaviour at just one specific level. Interactions and feedbacks across scales thus strongly determine earth system dynamics (Schellnhuber 1998). Unfortunately, 'scale' is one of the most abused notions in earth system research. Originally, when solely used for cartographic mapping purposes, scale was well defined and indicated smallest detail that still could be displayed. Large scale maps display many details, while small-scale maps display few. Currently, scale is more and more used to indicate the duration, extent and level of different spatial, temporal or organisational features. Fine scales display spatial, temporal and organisational detail, while coarse scales cover large regions, periods or whole nations. In order to avoid confusion, I'll use this 'fine' and 'coarse' terminology throughout the chapter and leave "small scales" and "large scales" solely for mapping purposes. Scale refers to the dimensions, in space, time or organisational level, of a particular object, system or phenomenon (O'Neill and King 1998). These are measured by the appropriate sub-components (i.e. the unit of analysis) and expressed in obvious units, such as meters or years. Scale has three major components: extent or duration, resolution, and grain (Blöschl and Sivapalan 1995; Figure 4.1.1). The extent or duration defines the boundaries, the area or the magnitudes. Resolution defines the finest detail that is distinguishable. The grain is the finest detail that is internally homogeneous. In principle, scales related to the physical and temporal dimensions are continuous and resolutions are generally selected in a very pragmatic way depending on, for example, data availability. The physical dimensions define data structure, which is generally spatially or temporally explicit. Organizational scales are generally discrete (e.g. individual, family, community, municipal, province, country) and not continuous. Even the grain could vary (e.g. small and larger countries). Organisational data is available in a tabular format for the specific level. The word 'level' is used here to describe the discrete scales of social organisation. Scale is also closely related to predictability: fine-scale events show more variability than coarse scale events do. This is because the effects of local heterogeneity are averaged out at coarser scales, so that patterns become more predictable (Levin 1992). On the other hand, studies focussing on broad-scale patterns lose predictive accuracy at specific points in space and time (e.g. Costanza and Maxwell 1994). Determining the optimal scale and interactions with lower and higher scales or levels of your specific global change research field is one of the major challenges and depends on the scientific research question(s) or the objective(s) of the study. This chapter deals with scale issues. First, I will further discuss why scale matters. Then, I will present some empirical, modelling or assessment studies that integrated processes along different dimensions and different scales. Finally, I present and discuss the different dimensions and related scale levels required in comprehensive analysis of the earth system. The dynamic behaviour of the earth system is central in this discussion. Many other studies have emphasised the behaviour of individual components and the factors that influence them. These factors are termed drivers. I will especially focus on the interactions between drivers and the different components of the earth system. This illustrates the complexity of earth system analysis and explicitly highlights the importance of scales at which processes and drivers operate and interact. It further allows improving the integration of natural (e.g. ecological, chemical and physical) and human (e.g. economic, social and cultural) processes. This provides adequate guidelines of how to deal with scale issues in global-change studies. Unfortunately a comprehensive earth system science with proper illustrative examples has not yet emerged. Therefore, I will present many examples from my own discipline land-use and ecosystems research. © Springer-Verlag Berlin Heidelberg 2006.