For each nation with reliable data, they calculated how many planets would be needed to support the global population if everybody adopted that nation's lifestyle as it was in 1978, and in 2003. They then expressed each figure as an Earth-equivalent ratio (EER) and plotted each value against the nation's corresponding UN Human Development Index. The index is a score of between 0 and 1, and is a function of a country's average life expectancy, adult literacy, level of schooling and per capita GDP.
To develop sustainably, the researchers assume a country must have an HDI of at least 0.8 and a maximum EER of 1 (see Diagram). A lower HDI would mean a nation is not developing adequately, while a higher EER means it is gobbling up too many resources.
By looking at each country's historical trajectory, a clear pattern emerges. People everywhere have a better lifestyle, but their footprint is growing at a rate proportional to their wealth. Developed countries in particular have done very little to reduce their impact. Only one nation, Cuba, is developing sustainably, and probably not for long (Ecological Economics, DOI: 10.1016/j.ecolecon.2007.08.017). "Cubans have high life expectancy and literacy, and were forced into a smaller footprint because of the oil embargo," says Wackernagel. "But they are now economically more successful, and will tend to use more resources."