Too often environmental debates turn on rhetoric and emotion rather than carefully considered data and analysis.¹ Firmer factual foundations and a higher degree of analytic rigor would help to narrow the range of dispute over which environmental battles rage and to move us beyond the current polarization over how best to achieve environmental goals.² At the heart of any shift toward more systematic environmental decisionmaking lies a need for reliable environmental "indicators" or "metrics" and other data that clarify the issues and the trend lines. To facilitate such a shift in environmental policymaking toward firmer underpinnings, the World Economic Forum's Global Leaders for Tomorrow Environment Task Force launched an initiative in 1999 to develop an Environmental Sustainability Index (ESI), the first full-fledged version of which has just been released.³