Human-induced global environmental change has emerged as one of this millenium's defining scientific and societal challenges. The scientific problem of global environmental change requires an understanding of the different components of the Earth's environment, from the atmosphere to the ocean to the biosphere, and of the many ways they interact. Because of this, global change science is an intensively cross-disciplinary research endeavour.

Key interdisciplinary problems in this field for the coming two decades include:

• Chemistry-climate feedbacks, which influence the lifetime of many greenhouse gases and the radiative properties of clouds, and hence the radiative forcing of the climate system.
• Ocean circulation effects, which influence the timing and spatial structure of the global climate system response to anthropogenic climate change.
• Biospheric uptake and processing of greenhouse gases/global change ecology. At present, about half of the CO2 emitted to the atmosphere is taken up by the biosphere and oceans. In the case of the biospheric sink, there is a growing consensus that much of this carbon reservoir is located in the forests and soils of the extra-tropical northern hemisphere, but there is high uncertainty as to the exact location and nature of this reservoir and its future stability.
• Global changes in hydrological and hydrogeological systems. Major changes in the distribution of atmospheric moisture and precipitation patterns will substantially alter the distribution and dynamics of the water cycle in the air, land and oceans. Inevitably, these changes will have a major impact upon water quality.
• Global changes in the linkages between physical and biological processes. The function of the earth system is highly dependent on the living world. As the system changes, the properties of the Earth's biological systems change along with the composition of species, and organisms adapt to changes in Earth's climate and hydrology. When considering the scientific aspects of global change, the academic community faces a two-fold challenge: through research to develop a comprehensive understanding of the scientific basis of the problem, and through education to convey this understanding to the next generation of researchers and decision makers.

In response to these challenges, the University of Toronto Centre for Global Change Science was formally established in September 2005 with the generous support of the University of Toronto's Faculty of Arts and Science "Academic Initiatives Fund". The mandate of the Centre for Global Change Science is to serve as the University of Toronto's focal point for research and education in Global Change Science. The research component of this mandate promotes interdisciplinary research programmes whose goal is to better understand and predict the global scale effects of human society on the earth's climate and environment. The education component of this mandate promotes a coordinated undergraduate and graduate education programmes to help develop the next generation of researchers and decision makers in Global Change Science.

The Centre harnesses the full breadth and depth of research and educational activities in several departments including Chemistry, Ecology and Evolutionary Biology, Geography, Earth Sciences and Physics, as well as ongoing work in the Faculties of Applied Science and Forestry. It serves as an interdisciplinary nexus for fostering new interactions, disseminating information, and attracting new sources of external funding. By providing a means to more strongly concentrate the research and educational activities at the University, the Centre will enable a more focused attack on the key sources of uncertainty in our understanding of the Earth System.