Estimates made just before the 21st century indicate that, by the year 2100, Earth may have between 10 and 11 billion people - not quite double the 6 billion population count reached in October 1999. Sustainable use of the planet requires that human needs be met without impairing the integrity of the planet's ecological life support system. This objective will almost certainly require equity and fairness in resource allocation among members of the human species and with natural systems upon which human depend. For the first time in history, humans have the power to create serious disequilibrium in natural systems at a global level. Nature is not vengeful, but it is opportunistic; new 'equilibrium conditions' are likely to be far less favorable to humans than present conditions. To prevent disequilibrium, a new ethos or set of guiding beliefs regarding human society's relationship with natural systems is essential. The best descriptor of the new ethos is eco-ethics (www.eeiu.org) guided by ethical science and implemented by compassionate, reasoned environmental politics. ESEP, the publication organ of the Eco-Ethics International Union, should be a powerful force in developing the necessary integration of science and value systems while maintaining the integrity of both.