Almost every scientific discipline uses "models". However, on closer inspection a large variety of different approaches are labeled as "models". For some scientists models are per se complex numerical models implemented on computers, but for other disciplines models take the form of mechanical analogs. Still others consider "models" to be preforms of theories or to be restricted concepts, within which basic dynamical (natural science as well as social science) aspects can be understood and described. Some models are not built in a systematic scientific manner, but evolve through social processes, and become powerful agents in the political arena. Thus, the applications of models range from conceptualisations, illustration to guidance of the decision process in everyday life and world politics.

Thus, models are a key concept in sciences, and specifically so in environmental sciences, where experiments can hardly be conducted because of the open and non-replicable character of environmental systems. Much too often modeling is seen and taught as a mere technical process of differential equations, numerics and computation, while the philosophical implications (the role of models in the process of generating knowledge) are not really thought about. This is a rather unfortunate limitation, as it prevents scientists from both acknowledging the inherent limitation of models and their applicability and fully exploiting their potential in providing added value to observations and theories. Therefore the topic "Models in Environmental Research" was chosen for the Second GKSS School of Environmental Research, which was held on 23-30 September 1998 in the Zündholzfabrik on the bank of the river Elbe in Lauenburg near Hamburg. As with the First School "Anthropogenic Climate Change" the lectures of the Second GKSS School of Environmental Research "Models in Environmental Research" are collected in this volume. The philosophy of modeling from the standpoints of a sociologist and of a natural scientist are discussed in the first two chapters. The physical and mathematical principles in constructing dynamical models are presented in Chapters 3 to 6, covering examples from oceanography and meteorology. In contrast, different modeling concepts in ecology and material research as well as morphology are offered in Chapters 7 to 9, while the use and role of statistical techniques is presented in the last two Chapters 10 and 11.

Before acknowledging the help of organisations and people in setting up the school, a few words about GKSS, its environmental research activities and the school may be in order: GKSS is a member of the Hermann von Helmholtz Gemeinschaft Deutscher Forschungszentren (HGF). Part of its research addresses environmental problems with emphasis on water and climate in the coastal zone. Its main interests are related to regional climatology and climate change, with interdecadal variations in the state of the coastal oceans and the flow of heavy metals, nutrients and other materials in river catchments to the coastal zones. This research aims at the understanding of changes in the environment, both because of internal (natural) dynamics and because of anthropogenic interference. In order to disseminate results of this research as well as to initiate a broad discussion among senior scientists in the field and younger colleagues from all over the world, the Division of Environmental Research at GKSS has institut 
While the second school was funded mainly by the GKSS Research Centre, it received significant financial assistance through the Verein der Freunde und Förderer der GKSS, Carl Duisberg Gesellschaft, University of Hamburg, and the German Climate Computing Centre. The technical and administrative support of Ilona Liesner and Beate Gardeike is gratefully acknowledged.

Hans von Storch, Lauenburg, 20 May 2000

Contents of Proceedings