Why energy?

Energy correlates to human activity

Natural processes, through their evolution over millions of years of time, are very energy-efficient. Artificial processes are, in contrast, very inefficient. The most destructive processes we undertake, for instance mining, electric generation and automotive transportation all consume very large amounts of energy. The extent to which artificial (and therefore environmentally damaging) processes correlate to higher energy processes is often surprising and amazing. Take for example, farming. The artificial chemicals that are used by industrial farms in fact require larger amounts of energy to produce, so that even an environmental issue as subtle as organic foods is reflected in the products' energy content.

Energy provides a numeric scale for consumer and policy decisions

Since lifecycle energy analysis yields a single, numeric value that is a rough equivalent to a given product's total environmental impact, one can easily compare the relative environmental importance of unrelated products and activities. For instance a decision to drive your car from one location to another may have the same environmental impact as 1,000 choices between paper or plastic bags at the grocery store. Consumers benefit from this information because it allows them to focus on the important decisions, and stop worrying about the unimportant ones. Advocates and policymakers also benefit in the same way, by knowing which issues are worth substantial attention, and which not.

Energy is the ultimate limit to a sustainable economy

Every day, the earth receives a great deal of energy from the sun. This energy is "free" to us; it comes with no environmental costs. It is also the only source of energy that is, for all practical purposes, infinite in supply. As we look forward to creating a sustainable economy for the planet, a project that will take hundreds of years to complete, it becomes clear that the sun is the only source of energy we can rely on indefinitely. The amount of energy we receive from the sun each day is very well known, so it is extremely important to understand how much economic activity the environment can support on an energy basis.

Fortunately, we can reap solar energy in many ways. Photovoltaic cells and solar thermal plants both recover solar energy directly. But solar energy also powers the natural processes that create wind, running water and biomass, all of which can be used to generate electric and heat energy as well.

Energy content is a window into climate change

Probably the single greatest threat to our environment at this moment is global climate change. A primary contributor to this problem is carbon dioxide, a by-product of combustion-based energy generation. By cataloguing the type of energy involved in each phase of a product, we can also measure that product's contribution to climate change, a subject of immediate importance.

Balance equations are possible

Energy is the most fundamental quantity recognized in the science of physics. Especially important, energy is a "conserved" quantity: it cannot be destroyed or created. This means that calculations ILEA makes regarding energy use in natural and human-influenced ecosystems can be checked for accuracy using energy balance equations: the energy input into a system must be exactly equal to the energy output.

One special application of energy balance equations is the calculation of the Earth's maximum sustainable carrying capacity. This is the maximum number of human beings the planet can carry while maintaining a functional ecosystem running on solar energy alone (since this is the only source of energy that will last indefinitely). Preliminary estimates of the carrying capacity are approximately 2 billion people; the current world population is already three times this number! More precise calculations of the carrying capacity are necessary, and measures of the total energy impact of various lifestyles are fundamental inputs to this calculation.

Last Modified on Sept. 12, 2003.

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