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Starting with the Basics: What to Measure?

Global energy resources comprise both stocks and flows. Stocks of energy exist in the form of potential chemical and atomic energy in fossil resources.4 Flows exist, for example, in the form of insolation, winds, tides, and hydro and geothermal energy. Finding a way to measure both stocks and flows in comparable units constitutes the first major challenge.

In any case, it is not enough to measure energy stocks and flows. What defines an energy resource is its ability to be transformed into an energy service. Energy services created by energy use, rather than simply energy use per se, contribute to human well-being. The value to future generations of a particular physical energy resource, such as a ton of coal, is proportional to the efficiency with which it can be transformed into an energy service, such as lighting. Therefore, it is not enough to measure energy resources. We must also measure the rate at which they can be transformed into energy services; that is, we must measure energy efficiency.

In this volume, Worrell points out that improvements in energy efficiency allow less energy to be converted to more energy services, thereby effectively expanding the utility of existing energy resources to society. In addition, as Wilbanks (this volume) demonstrates, the use of energy is interdependent with other key resources necessary for human well-being. For example, burning fossil fuels produces greenhouse gases and other environmental pollutants. Substituting biomass for fossil energy at a scale meaningful to the global energy supply competes with the global food supply.

As Worrell points out, methods of decomposition analysis, such as divisia, can be used to measure trends in energy use and related human activities. In general, the ratio of energy to gross domestic product has been declining over time as energy efficiencies improve and as economies shift from more to less energy-intensive activities (Figure 20.2). These measures of energy intensity illustrate how physical measures of energy resources could be rescaled over time to better reflect their ability to provide for the needs of future generations.

In many ways, GDP is an inadequate measure of human well-being, in that it omits such fundamentally important factors as environmental services. Fortunately, more comprehensive GDP measures have been developed and could be applied just as readily for measuring the sustainability of energy resources. For example, Goldemberg and Johansson (2004) have shown how the human development index (HDI) relates to per-capita energy use in a very nonlinear way; wealthy people use more energy per income (Figure 20.3). While energy use generally increases with increasing income, the HDI indicates that equal levels of well-being can be achieved with very different levels of energy use, especially for the world's wealthier economies. How societies

Here I arguably include uranium among fossil resources despite its very different origin from hydrocarbon fossil fuels.

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