The most widely used social, economic and environmental indicators are scale, sector or subject-specific. Indicators for sustainable development, however, need to address the linkages between different aspects of global change and this requires a systemic approach. One way of systematically structuring the interlinkages between indicators is by using integrated assessment models. In this chapter we discuss indicators from a modeller's point of view, including their use for communicating model results. A hierarchical framework is introduced for models in general and TARGETS in particular.

Introduction

Indicators are pieces of information designed to communicate complex messages in a simplified, (quasi-)quantitative manner so that progress in the field of decision-making can be measured. Social and economic indicators have been used for decades at both the national and international level. More recently, environmental indicators have been developed, which are not yet as widely adopted as socio-economic indicators. The most widely used social, economic and environmental indicators are scale, sector or subject-specific. Indicators for sustainable development, however, need to address the interlinkages between the social, economic and environmental aspects of sustainable development. Because there are so many different linkages at different levels, this requires a systemic approach. One way of systematically structuring the interlinkages between indicators is by using models, in particular integrated assessment models.

Chapter 40 of Agenda 21 (UNCED, 1992) calls for the development of indicators for sustainable development, at multiple levels. Indicators for sustainable development are needed in order to provide decision-makers with information on sustainable development that is simpler and more readily understood than raw or even analysed data (Billharz and Molda, 1995).