More than at any other time in the history of human civilization, we can’t project where we are heading by looking at where we have been. Why is our time unique? We are experiencing accelerating climate change due to human activities, and this will continue through the coming century, taking us into climates not previously experienced by modern humans. Our lifestyles are profoundly dependent on a fossil fuel resource (now about half-depleted), whose combustion is responsible for these changes. Human population is increasing at a rate that will add 2-3 billion to the human population over the next generation, raising concerns for the sustainability of food production and for the compatibility of human well-being and conservation of natural systems. Extinction rates have accelerated as humans have massively rearranged ecosystem function to serve our needs, and humans now use 1/3-1/2 of all biological productivity of planet earth. New diseases (human, animal, and plant) are emerging due to environmental change. Because these trends and conditions are without precedent, our projections for the future are inherently uncertain, but we must make policy and plans on the basis of our best estimates. What are the likely (or worst-case) consequences for human welfare and futures? Can democratic institutions respond effectively to long-term threats to the sustainability of human societies? We will use conceptual background and tools from a range of disciplines to better understand issues springing from global environmental change.