How much is a cleaner environment worth? For policy makers, that question used to go largely unanswered. Many economic activities cause environmental degradation, entailing real costs to the economy and to people's welfare. Knowing the extent of these costs is crucial for identifying a country's main environmental priorities and allocating appropriate funds for environmental protection. Over the past decade, the World Bank has initiated a systematic effort to measure the costs of environmental degradation in the Middle East and North Africa, shedding new light on their magnitude and on the...