Many countries around the world are experiencing a demographic transition that is occurring due to increased longevity combined with low fertility rates. However, demographic momentum means that the global population is expected to continue to increase until at least the middle of the century, likely peaking near 10 billion.

Ian Johnson was Former World Bank's Vice President for Sustainable Development (ESSD) and has over thirty years experience in economic development. He spent twenty-six years at the World Bank, starting as an energy economist and financial analyst and working through increasing levels of responsibility was, for his last eight years, Vice President for Sustainable Development and, for five years, also Chairman of the Consultative Group on International Agricultural Research (CGIAR). Prior to joining the World Bank, he was an economist with the British Government and he spent five years in Bangladesh working with the United Nations and a non-government organization. Since leaving the World Bank Ian Johnson has been an advisor to the government of Chile, a member of the Swedish Commission on Climate Change, senior advisor to GLOBE and chair of its Ecosystems Services Panel, as well as consultant to a number of international organizations.

"Optimum population" is a subject long discussed in welfare economics. The talk will first discuss the framework for analysis of policy. This leads to a discussion of the implications of population growth for justice at a global level and the evolution of global inequality. The final part of the talk is concerned with population growth and the setting of global goals post-2015. Professor Sir Tony Atkinson, Deputy Director, Institute for New Economic Thinking @ Oxford; Professor of Economics, Oxford University.

Talk by Professor Robyn Norton, Co-Director, George Centre for Healthcare Innovation. The successes of the past century in reducing childhood mortality and eradicating many infectious diseases. have contributed to growing numbers in the population reaching adolescence and middle age - not only in high income countries but also in low and middle-income countries. Concurrently, this population growth has been accompanied by increasing numbers engaging in unhealthy behaviour, such as smoking, reduced physical activity and overeating. Such behaviour has led to overweight and obesity, thus contributing to growing numbers of people sustaining chronic diseases. Providing safe, effective and affordable healthcare to manage these chronic conditions, not only for those in high income countries but also for those in low and middle-income countries, is a significant challenge for governments globally and an opportunity for innovative minds to find practicable solutions.

Professor Guy Houlsby, Co-director, Programme on Globalising Tidal Power Generation (Member of Oxford Martin School).

Talk by Professor Charles Godfray, Director, Oxford Martin Programme on the Future of Food. The global food system is undergoing a significant phase change that will see an end to the historically low food prices that we have experienced over the last four decades. Challenges on both the supply and demand side suggest that if current trends and practices continue we shall see very significant increases in food prices with threats to the sustainability of food production and particular harm to the world's poorest. This talk explores how food supply, food demand, and food system efficiency and governance needs to change to meet these challenges.

'Water Crises', 'Water Wars', 'Peak Water' and many more phrases have been used in recent years to suggest that a growing population and increased per capita water use are leading inexorably to critical levels of water scarcity. In this talk, the factors affecting water availability and water use are explained and the links between water use, population growth, economic output, social welfare and ecosystem services are examined. Against this background, alternative 'water futures' are presented to illustrate the potential for sustainable water use, and the challenges of imagination, economics and governance that may be required to steer a path to sustainability.

It is common to hear about the problems of overpopulation, but do we really have too many people? Do we have an acceptable number? Or might we even have too few? Toby Ord shows how we ignore the good side of having a large population, how we can weigh the benefits and drawbacks of having a large population, and how future technologies could create a moral imperative to massively increase our population in the 21st century and beyond.