Human activities have a measurable influence on many aspects of the Earth's environment. Nearly 50% of the land surface has been transformed by direct human action, with significant consequences for biodiversity, soil structure and climate. More than half of the accessible freshwater is used directly or indirectly by humankind, and underground water resources are being depleted rapidly in many areas. The atmospheric concentrations of several important greenhouse gases have increased rapidly since industrialisation began, with potentially dramatic consequences for the Earth's climate. Coastal and marine habitats are being altered at a rapid rate, while fisheries world-wide are being depleted.

Scientists world-wide have been studying the causes and consequences of such changes, as well as the possible responses. It has become clear that understanding these global environmental changes needs coordinated contributions from natural scientists, such as ecologists, climatologists and oceanographers, as well as from social scientists, for example economists, anthropologists and sociologists.

Research on the human dimensions of global environmental change investigates the human causes and consequences of change, as well as the human responses to change. This research is interdisciplinary and requires input from scholars in developed and developing countries. Global environmental change research in recent years has increasingly recognised the importance of including humans as a central part of the Earth System (see IGBP Science 4: Global Change and the Earth System: A planet under pressure).

The International Human Dimensions Programme on Global Environmental Change (IHDP) is playing an important role in this development. (Core Science Projects) IHDP has seven Core Science Projects. All are managed through International Project Offices located around the world. (Joint Science Projects) IHDP and its partner programmes on global environmental change - IGBP, WCRP and DIVERSITAS - (Partners) collaborate on three cross-cutting research themes: global food systems, the global carbon cycle and the global water cycle. A project on human health with regard to GEC is in the Planning phase. (Collaborative Projects)