Entropy revisited

by Guy R. McPherson | Nature Bats Last in Energy Bulletin | Feb 5 2010

You can't win, you can't break even, and you can't get out of the game. Those kernels are my favorite descriptors of the Three Laws of Thermodynamics. Respectively, the clauses mean (1) energy is conserved (First Law), (2) entropy never decreases, thus precluding perpetual motion machines (Second Law), and (3) it is impossible to cool a system to absolute zero (Third Law). The Second Law in particular puts insurmountable, irreversible constraints on everything we do. Without the Second Law, there would be no heat losses in energy systems, and electricity would be far too cheap to meter and commodify.

One way of looking at our current set of predicaments is that we've been on a binge, consuming energy considerably faster than it can be captured and stored by Earth's ecosystems. While fossil fuels once appeared limitless (and still do to deniers of peak oil), and though we're literally bathed in energy (in the form of sunlight), the disappearance of the fossil-fuel storehouse accumulated over millions of years isn't something that can be replaced with anything nearly as convenient as fossil fuels. Solar, wind, wave, geothermal, nuclear, and hydropower simply don't pack the same punch as fossil fuels, either singly or in combination. In short, we're falling off the net-energy cliff, and there's no lifeline to grab onto, no known technology to break the fall.

Long before the Industrial Era, work such as growing food, manufacturing goods, and distributing materials was accomplished via the limited power of human muscle (the monuments of the ancient world all being built with slave labor) and draught animals. Later, water wheels and windmills enabled us to convert force into mechanical power. The steam engine and combustion engine now allow us to tap the huge energy storehouse represented by fossil fuels and perform work we could not have done before, which translates into the sudden, exponential rise in human population and rapid destruction of the natural world. The differential between muscle power and simple mechanical power versus that harnessed by the application of fossil fuels can hardly be overstated. The trend from animal slaves (including humans) to fossil-fuel slaves seems like a one-way street, considering the paucity of draught animals and sanctioned slavery relative to the human population, but it isn't. Enslavement to fossil fuels ends when the now-abundant supply turns to scarcity, at which point radical austerity sets in.

Three attributes of fossil fuels are particularly noteworthy. First, fossil fuels -- especially crude oil -- have amazingly high energy density. If you've burned oak in a wood stove, you have witnessed the heating power of 6,000 Btu per pound. Depending on the type, coal contains 8,000–14,000 Btu per pound. The devil's excrement blows away wood and coal at nearly 20,000 Btu per pound. Once found, coal and oil are much more convenient to extract and deliver than wood, which explains in part why so many more railroad hopper cars are filled with coal than with firewood.

The second characteristic favoring consumption of fossil fuels is energy return on investment (EROI, sometimes expressed as EROEI for energy return on energy invested). Charles Hall is the primary authority on this subject, and his primer at The Oil Drum illustrates the importance of EROI while also showing how rapidly EROI has declined for U.S. oil. Specifically, average EROI of U.S. crude oil dropped from 100:1 in the 1930s to 30:1 in 1970 and down below 20:1 today while EROI for coal has varied from 40:1 to 80:1 during the same period. Meanwhile, firewood has an EROI of about 30:1, much higher than nuclear or solar photovoltaic (PV) and about the same as hydropower (we've nearly run out of rivers to dam, at least in North America).

The third big issue regarding fossil fuels is their potential energy. Coal and oil are just lying underground, containing dense sums of energy, begging us to gobble it up for our own immediate use, leaving nothing behind in the quintessential capitalist game of heedless maximization (e.g., Daniel Quinn's theory of leavers and takers). There's no need to turn a turbine with the quaint use of wind or water to generate electricity. There's no need to bust apart atoms through exotic, risky, and expensive means that produce the nastiest of all wastes. Insatiable vampires, we jam our fang-like straws into the ground to extract easily combusted ancient sun-blood.

It's easy to understand why we committed to crude oil early in the industrial game. Its energy density, EROI, and convenience of combustion are irresistible. It's small wonder, then, that we developed an entire civilization based on fossil fuels. The physics underlying the conversion of energy into heat, power, force, or work is a tangle of interrelated concepts not easily sorted out by nonscientists. However, whether various inputs and outputs are measured in watts, Btu, calories, joules, newtons, or volts, what's clear is that civilization is currently engorged, literally feasting on fossil fuels. But it's not anything close to a zero sum game, where resources stay constant and are only shifted around over time. Rather, the Second Law guarantees there is always a diminishing return.

Ultimately, all this points to a future in which we will be energy poor because we've used up the storehouse of cheap, convenient energy. In the not-so-distant future, the purportedly nonnegotiable American way of life, which is based on inexpensive and rapid movement of humans and materials via conversion of stored energy to mechanical power, will no longer be possible. Put in more immediate terms, there will soon be a time when old folks say with some nostalgia, "Oh yeah, I remember warm showers."

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The initial draft of this essay was prepared by Brutus, who contributed considerable editorial expertise toward later drafts.

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