An empirical environmental Sustainability Index derived solely from nighttime satellite imagery and ecosystem service valuation

This paper describes a crude yet simple Environmental Sustainability Index (ESI) derived solely from the ratio of two classified satellite images with global coverage. An ESI is calculated for each nation of the world by dividing the amount of light energy emitted by that nation as measured by a nighttime satellite image into the total value of that nation's ecosystem services as measured by a land-cover dataset and ecosystem service values estimated,by Costanza et. al. (Costanza, d'Arge et al., 1997). The strength of this ESI is its simplicity and global coverage (other ESIs involve hundreds of variables which usually entail many 'data gaps'). The utility of this ESI is not as 'the' measure of environmental sustainability but as 'a' measure that can be compared to other ESIs in interesting and informative ways. Measuring environmental sustainability is a difficult challenge that is being undertaken by more and more people and institutions using a wide variety of methods. If independent measures of sustainability do not correspond reasonably well with one another then the practical utility of deriving ESIs will be undermined because the exercise will be perceived as more political than scientific. Two sophisticated ESIs are examined and compared to this simple one: 1) The 2001 Environmental Sustainability Index derived as an initiative of the Global Leaders of Tomorrow Environment Task Force, World Economic Forum, and 2) Ecological Footprints of Nations: How much Nature do they use? How much Nature do they have? developed by Mathis Wackernagel and others as a "Rio + 5" forum study and financed by The Earth Council in Costa Rica. These two indices are a composite of many sub-indices some of which correlate highly; however, the final nationally aggregated figures of the 2001 Environmental Sustainability Index and the comparable Ecological Footprint index do not correlate at all. The Eco-Value/Night Light index described here corresponds strongly with the Ecological Footprint Index and not at all with the Environmental Sustainability Index. Some of the implications of the lack of coherence between these three measures are discussed.