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“Drill, baby, drill” has become a slogan of those who want to produce more oil and gas and who scoff at alternatives to petroleum. But rarely mentioned is the expense required to get that oil and gas—and still more rarely mentioned is the energy required to access those resources.
Charles Hall, an ecologist at the State University of New York College of Environmental Science and Forestry in Syracuse, has spent most of his long career trying to get fellow researchers and the public to take a serious look at the energy required to get the energy we use. He is given credit for creating a measure known as the energy return on investment, or EROI—the ratio of energy output over energy input. (With oil, for example, the energy output would be the crude oil produced, and the energy input would be all that required to find the oil reservoir, drill the well and pump the oil out of the ground.) EROI is a crucial metric, Hall argues, because it helps us see which energy sources are high quality and which are not.
Hall and his students did pioneering work in this area, including a 1984 paper on the cover of Science. For many years, however, interest in the topic languished. But recent soaring oil prices and increasing difficulty of accessing new supplies have helped create economic hardships, leading to resurgent interest in EROI. Scientific American asked Hall to explain the basis of the EROI and how it pertains to our economy.
[An edited transcript of the interview follows.]
You’re a self-described “nature boy” who became an ecologist. So how did you create the idea of energy return on investment (EROI)?
I had this unbelievable doctoral advisor, H. T. Odum of the University of North Carolina in Chapel Hill. He said, “Well, Charlie, I don't think anyone has thought about fish migration from a systems perspective.”
I went down to the coast of North Carolina, looking for a place where I could do this research. And I found one: in this freshwater environment, where fish weren't supposed to be migrating, they were migrating like crazy.
And you approached this migration mystery from an energy-use perspective. How did you do that?
I measured the ecosystem productivity by the free-water oxygen technique. I measured it at five different places, upstream and downstream, and found some very clear patterns. The energy available to the fish was much more concentrated as you went upstream, and I developed this theory that the fish would migrate to capitalize on the abundance of energy for the first year or two of the life, and then the young fish would migrate downstream into a more stable but less productive environment.
The study found that fish populations that migrated would return at least four calories for every calorie they invested in the process of migration by being able to exploit different ecosystems of different productivity at different stages of their life cycles.
So from studying fish migration, was it a big leap to think about people and fossil fuels?
No, probably because Howard Odum was evolving in his thought processes. He wrote a book Environment, Power and Society at about that time. An amazing thing working with Odum was, for him, there are just systems. It doesn't matter if it's a forested system or a stream system or an estuarine system, or whether people are there or not. It's just a system—and systems have many similar patterns and many similar processes of consumption and production, and they often even have similar controls on them.