Measuring Energy Sustainability

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David L. Greene


For the purpose of measurement, energy sustainability is defined as ensuring that future generations have energy resources that enable them to achieve a level of well-being at least as good as that of the current generation. It is recognized that there are valid, more comprehensive understandings of sustainability and that energy sustainability as defined here is only meaningful when placed in a broader context. Still, measuring energy sustainability is important to society because the rates of consumption of some fossil resources are now substantial in relation to measures of ultimate resources, and because conflicts between fossil energy use and environmental sustainability are intensifying. Starting from the definition, an equation for energy sustainability is derived that reconciles renewable flows and nonrenewable stocks, includes the transformation of energy into energy services, incorporates technological change and, at least notionally, allows for changes in the relationship between energy services and societal well-being. Energy sustainability must be measured retrospectively as well as prospectively, and methods for doing each are discussed. Connections to the sustainability of other resources are also critical. The framework presented is merely a starting point; much remains to be done to make it operational.


Energy is the only universal currency: one of its many forms must be transformed to another in order for stars to shine, planets to rotate, plants to grow, and civilizations to evolve (Smil 1998:10).

As Solow (1992) has pointed out, "the duty imposed by sustainability is to bequeath to posterity not any particular thing," but to ensure that future generations have the opportunity to "achieve a standard of living at least as good as our own."1 Solow's interpretation of sustainability differs from the seminal

This idea is borrowed from Sen (2000).

statement by the Brundtland Commission (WCED 1987) in one key respect: The Brundtland definition requires that the current generation not diminish the ability of future generations to meet their "needs" rather than requiring that they be ensured the opportunity to achieve at least as good a standard of living. If needs are defined as only the most basic requisites for survival, then the two definitions are far apart. However, if a need is defined as, "a lack of something requisite, desirable, or useful" [emphasis added], as per Merriam-Webster's, then it is possible to argue that the two definitions intend the same meaning. The position taken in this chapter is that sustainability should be interpreted as ensuring that future generations have the opportunity to achieve a level of well-being2 at least as good as that of the current generation. Our objective for energy is that of this Forum as a whole:

To measure the stocks, rates of use, interconnections, and potential for change of critical resources on the planet, and to arrive at a synthesis of the scientific approaches to sustainability.

This is quite different from measuring energy for sustainable development, which has been addressed in depth elsewhere (e.g., Goldemberg and Johansson 2004). Sustainable development is concerned with simultaneously achieving economic growth, social progress, and environmental protection. Its objectives are most clearly articulated by the Millenium Development Goals enunciated by the Millenium Summit held in 2000 at the United Nations General Assembly. By comparison, our goals are more limited, yet extremely challenging.

By focusing on energy sustainability, we do not mean to imply that there are no opportunities to substitute other factors for energy in order to maintain or increase human well-being. However, energy is so fundamental to society that opportunities for substitution are limited. Most such opportunities arise from the fact that societies are not interested in using energy per se, but rather in the services that energy can provide.

The objective of an energy system is to deliver to consumers the benefits that energy use offers. The term energy services is used to describe these benefits, which for households include illumination, cooked food, comfortable indoor temperatures, refrigeration, telecommunications, education and transportation (Goldemberg and Johansson 2004:25).

Sustainability is more about rates of change than it is about stocks. To measure energy sustainability, one must measure the extent, rate of use, and rate of creation and expansion of the ability to produce energy services and, ultimately, the ability of energy services to produce human well-being. Therefore, one must also measure the extent to which energy use affects environmental quality, security, water availability, mineral resource availability, food supply,

Webster's 11th Collegiate Dictionary defines well-being as "the state of being happy, healthy, or prosperous: WELFARE." The consensus of our discussion group at this Forum was that "well-being" is appropriately broader and more flexible than "standard of living" or "needs."

and so on. It is possible to run out of resources. However, it is also possible to create new resources where there were none before. Moreover, resource creation is not only a matter of technological change; individual, economic, and institutional changes all have important roles.

Energy sustainability is not just about energy. It is also about the interrelationships between energy and other factors that affect human well-being. Humans' use of energy affects the environment, the supply of water, agriculture and food production, indeed every facet of society. Measuring the critical interrelationships is also necessary to measuring energy sustainability. In a report on scenarios of sustainable energy futures, the IEA (2003) identified two principal components of energy unsustainability: increasing greenhouse gas emissions and the security of energy supply. These are not the only sus-tainability issues linked to energy use. There are important linkages to water resources, agricultural land and natural habitats, as well as to minerals essential for catalysis and other critical uses.

In addition, energy sustainability must be measured retrospectively as well as prospectively. Sustainability is fundamentally about the future, about the obligation of current generations to future generations. However, the future is unknown. Loschel et al. (this volume) propose using scenario analyses to explore the sustainability of alternative future pathways. Identifying measures and estimating energy sustainability in alternative energy futures seems essential to formulating plans and strategies for achieving sustainability. Yet measuring sustainability in future scenarios is inherently speculative because scenarios, even if plausible, are inherently hypothetical. Retrospective analysis using equivalent measures provides a needed empirical test. We may be able to envision sustainable energy futures, but are we on a sustainable trajectory today? Have we been creating energy resources for future generations as fast as we are consuming stocks of energy resources? It seems essential to be able to measure both whether we have been sustainable in the recent past and whether we can envision a trajectory that could lead to a sustainable future.

Thirty five years ago, the book Limits to Growth had an important impact on how people thought about global society's relationship to the environment (Meadows et al. 1972). The book simulated many doomsday scenarios in which the world's economies either ran out of fundamental resources or polluted the environment so severely that it could no longer sustain human life on a large scale. The fact that none of the doomsday scenarios came to pass is often cited as proof that all such dire predictions will always be wrong. It is certainly true that the computer modeling on which the book was based underappreciated the roles of markets and innovation. However, Limits to Growth contained one very different scenario that is too often overlooked. In that scenario, rapid technological change, together with what may have seemed at the time to be draconian environmental regulation, permitted sustained growth of the global economy and population. Of course, it is precisely that scenario in which we live today. For example, thanks to innovation and regulation, today's automobiles emit 1% (or less) of the pollution than vehicles built over forty years ago. Pollution of air and water resources is now extensively regulated around the world, and international treaties protect certain key global resources, such as the stratospheric ozone layer.

Despite this remarkable progress, the world faces daunting environmental and resource challenges. Among these is providing sufficient energy for the world's growing economies without doing serious damage to the global climate system or inciting international conflicts over energy resources. Just as food is essential to living organisms, energy is essential to human society. Unlike food, which has been and continues to be a renewable resource, fossil energy has been a staple of human economies since the industrial revolution. For most of the past two centuries, the quantities of fossil energy resources extant in Earth's crust were vast in comparison to their rates of use by humans. Today, however, the rate of use of fossil resources is a matter of serious concern. In 1995, cumulative production of conventional petroleum amounted to 710 billion barrels,3 a significant fraction of the World Petroleum Assessment (WPA-2000) of ultimately recoverable resources of 3 trillion barrels (USGS 2000). By 2005, cumulative consumption exceeded 1 trillion barrels (Figure 20.1). Approximately one-fourth of all oil consumed throughout human history had been consumed in the last ten years. While the USGS and Colin Campbell (2005) disagree about the measurement of ultimately recoverable oil resources, by either measure the current rate of consumption is large relative to what remains. Moreover, the rate of use has been accelerating. The US National Petroleum Council (NPC) estimated that if trends continued, another trillion barrels of oil would be used up in the twenty-five years from 2005-2030 (NPC 2007). By any standard, such a rate of consumption must be considered large in relation to what we know of conventional oil resources. It is only prudent to ask whether such a rate is sustainable.

Yet, energy sustainability is not about running out of energy. As Holdren (2000) points out, the world is not in imminent danger of running out of energy altogether. However, the world's use of energy is running into conflicts with other things we value: environmental protection, economic growth, and equity, especially equity of access to energy, which affects equity of opportunity. This brings us back to Solow's definition. Energy sustainability is about ensuring that we leave future generations with an equal opportunity to use energy services to provide for their well-being. It seems likely that this will require an enormous amount of energy. What energy resources can provide the energy services needed in ways that maintain or enhance the sustainability of Earth's other critical resources?

To make progress in measuring the sustainability of energy resources, it is important to avoid unnecessary semantic confusion. The discourse must not be

Customarily, industrial convention quantifies oil in terms of barrels, where 1 barrel of crude oil = 0.15853 kilo liters; billions = one thousand million, or 109.

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