Friday, April 10, 2009

The Candy Bar Energy Diet

After becoming increasingly frustrated with insubstantial US network evening news shows, larded with equal helpings of “pessimism porn” and “feel good” stories, my wife and I recently switched back to BBC America. Last night’s news included a clever segment called, “The Ethical Man Reborn in the USA.” This featured a sardonically humorous reporter making his way across the country on public transportation to drum up concern about climate change. Yesterday’s program focused on a town hall meeting in Muskegon, Michigan, in which Mr. Rowlatt demonstrated America’s energy profligacy by converting our average daily energy consumption to its equivalent in candy bars. But while the unsubtle message of gluttony was delivered with a smile, my take-away was quite different from the intended one.

Before I could draw any serious conclusions from this little demonstration, I felt obliged to check his math. The most recent figures on per capita energy consumption from the Energy Information Agency reveal that the average American uses 337 million BTUs, or British Thermal Units, of energy in all forms per year. (That excludes the energy content of food consumed.) This works out to 233,000 kilocalories, or food Calorie equivalents, per day. Dividing by the 271 Calories in a Snickers bar gets us to 860, roughly the number of candy bars that Mr. Rowlatt showered on his audience by way of comparing our energy consumption to a daily food diet equivalent to 8-10 candy bars per person. In other words, Americans consume something like 100 times as much energy as food, thus contributing enormously—and more than most other countries—to climate change. He then swept all but a few of the bars off the table, suggesting that the heap on the floor represented the national energy diet we must go on to achieve an 80% reduction in greenhouse gas emissions by 2050.

As clever as this symbolism was--I admit I had never thought about our energy use in quite these terms before--there are a few problems with the logic, although the basic math is sound. For one thing, while our present energy mix, heavy in fossil fuels, makes energy and emissions largely synonymous, that would presumably no longer be the case in our low-emissions future. An 80% emissions cut can’t depend on an 80% energy cut, or we’ll all be starving in the dark, or at least leading lifestyles that most modern Americans would find pretty unappealing. As important as efficiency improvements are to achieving large emissions reductions, particularly early on, the long-term trend of civilization is increasing energy use, and sooner or later that will overcome efficiency. The key to achieving that 80% emissions reduction is a massive transition to low-emission energy sources. As we envision this today, that means renewables and nuclear power, with some proportion of lower-emission fossil fuels, presumably natural gas and carbon-sequestered coal. When that shift is complete, sometime later this century, we’ll still be energy gluttons in world-historical terms, but presumably cleaner ones.

OK, it’s a semi-humorous news segment and I shouldn’t scrutinize its message too deeply, right? But aside from its somewhat misleading conclusion, I found that the candy bar demonstration made tangible one of the main themes of this blog since I started it in 2004: The scale of our present energy economy greatly constrains the ease and speed of its transition to other forms. Consider biofuels. Thanks to the Green Revolution, a large continental land mass, and plenty of energy-intensive fertilizer, the US produces a substantial food surplus. We can feed ourselves abundantly and still have food left over to export to other countries. However, even the most optimistic estimate of future agricultural productivity must fall well short of assuming that we can produce energy crops equivalent to 100 times our food consumption, or even 50 times, allowing for an eventual doubling of our current energy efficiency. Even if we’re just looking at replacing our per-capita gasoline consumption, that would still require the equivalent of 36,000 Calories per day, or about 14X our food intake.

That comparison reinforces my conclusion that we cannot hope to rely solely on energy sources derived from photosynthesis—or with conversion efficiencies little higher than photosynthesis—to solve our energy and emissions problems. Advanced biofuels such as cellulosic ethanol still have the potential to be an important element of our future energy mix, but they can’t replace the concentrated energy we get from fossil fuels, and they may be no more than a bridge to a long-term energy economy based mostly on electricity derived from the atom, advanced solar and geothermal power, and augmented by intermittent power from wind, wave and tidal energy. After all, as I’m sure your mother told you years ago, we can’t live on candy bars.

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