# Energy in Nature and Society: General Energetics of Complex Systems

By Vaclav Smil
The MIT Press, 2008, 480 pp., ISBN 978-0-262-69356-9, $70.00 (cloth),$32.00 (paper)

Vaclav Smil, a prolific author of science-based books about energy, has updated some of his previous work, presenting here an encyclopedic study of energy as a unifying theme in the development of human society. He considers two eras: the pre-modern, in which agricultural technology provided the basis of increased human productivity beyond that of hunter-gatherer societies, and the modern, where access to fossil and other fuels vastly expanded human populations and individual potential. For those of us engaged in the study of energy use in developed and developing nations worldwide, some of which are in transit between these eras, this is a superbly documented (over a thousand references) and valuable resource for understanding the complexities of the human use of nature’s energy resources.

The first half of this book is concerned with the role of human and animal energy in producing the food and services that support human communities. The theme is agriculture as a component of net primary production in plant systems that support all life in the biosphere. Starting with the biochemical process of photosynthesis, he traces the energy paths that support heterotrophic ecoclimes which humans now manage rather than simply dwell in, sometimes destructively so. This biochemical energy cycle, powered by only a tiny fraction of the solar flux, is the prime mover of all biospheric life. Its agricultural component was the principal engine of economic growth prior to the onset of the industrial revolution.

Smil emphasizes that energy balance is only one factor in the human food cycle, and that other factors affecting nutrition are tightly linked to the minor cycles of nitrogen, sulfur, phosphorus, and other essential elements in the biosphere that is otherwise dominated by the carbon, oxygen, and water. Nevertheless, energy has great explanatory value in elucidating the basic fabric of life in all its forms.

Smil’s later chapters trace the new paths of industrial energies, embodied in fossil and nuclear fuels and renewable energy technologies. These energy fluxes are an order of magnitude larger than food energy, and their introduction has changed the latter as much as it has changed human societies. Industrial agriculture has quintupled the human population that can be fed per hectare of arable land. This has been possible through use of only a small fraction of the industrial energy supply and the efforts of the human population. Nevertheless, the global food supply cannot be much expanded by throwing more energy at it; it is limited by the supply of productive arable land, water, and ecological resources.

The industrial energy analysis proceeds along conventional paths. World demand and supply of industrial energy is summarized and energy fluxes are characterized. The ratio of embedded energy output to input, which the author calls the “energy return on invested energy” (not at all the energy equivalent of return on investment that interests Wall St. investors), is very high for fossil and nuclear fuels, but low for agricultural crops. This explains in part why fossil/nuclear resources are more economical to exploit than agricultural resources. Renewable energy is comparable to fossil fuels on an output/input basis, but is more capital intensive, which adversely affects its economic cost.

Smil also reviews the land area requirements for renewable energy systems. These are on the order of one square meter per watt of annual average electrical power output. Even so, this is a more energy intensive use for land than energy crops, and less environmentally intrusive.

Producing needed energy, while limiting climate change through reductions in greenhouse gas emissions, is now a global goal for both developed and developing nations. Finding the path forward towards this desirable future involves much more than a scientific and technological understanding of nature’s limitations on possible alternatives, which Smil’s volume lays out for the reader’s edification with economy and some elegance. It presents at least a good beginning for addressing this thorny problem.

Smil’s book appears at an opportune time. The current debate and controversy over the diversion of agricultural crops from food to vehicle fuel production has highlighted the need for agricultural scientists, energy scientists, and technologists to plumb the depths of scientific understanding of these essential industries and their connectedness to the future of both ecological and human communities. Smil provides a fine starting point for the needed dialog.

James A. Fay
Dept. of Mechanical Engineering, MIT
jfay@mit.edu

This contribution has not been peer refereed. It represents solely the view(s) of the author(s) and not necessarily the views of APS.