When We Eat, We’re Eating Energy

Herewith some startling numbers. A report by the Congressional Research Service in 2004 (link), provides direct and indirect energy consumed in Agriculture, including crop and livestock production. The numbers are in quadrillion BTUs, and the answer is that we consumed 1.7 quadrillion BTUs of energy, 1.1 quadrillion BTU in direct uses, and 0.6 quads in indirect, thus for fertilizers and pesticides. A USDA Factbook (link) tells us that “The aggregate food supply in 2000 provided 3,800 calories per person per day.” The (late) 2012 Statistical Abstract (link, Table 2) tells me that the 2002 population of the United States was 288.1 million people. So let us combine these numbers. Below the CRS data shown graphically:

Now one food calorie, also known as a kilo calorie, is worth 3.968320721 BTUs. Put another way, it takes 0.251995761 calories to make a BTU. So we can convert calories to BTUs or BTUs to calories. A quadrillion is 10¹⁵. Here is what it looks like: 1,000,000,000,000,000. So let us proceed.

If we apply year 2000 calories per capita to the 2002 population, we discover that in that year agriculture provided 1.1 trillion calories per day or 399.6 trillion calories a year to the total population. We can render that number into BTU-equivalents by either multiplying by 3.968… or by dividing it by 0.25199…. In any case we will be 1.584 quadrillion BTUs. That was the energy output of our agriculture in 2002 measured in quads of BTUs. So what did we expend in energy to get that output? What was the energy input? It was 1.7 quadrillions of BTU.

To get a ratio here, we take the input and divide it by the output. The result is 1.072. In other words, we expended more calories in industrial energy to get 1 calorie that we could eat. But the energy ratio calculation is not yet done.

We learn from this story in the Atlanta Journal Constitution, by William G. Mosely, co-author of a 2010 National Academy of Science study, “Understanding the Changing Planet: Strategic Directions for the Geographical Sciences,” that in addition to direct and indirect energy uses, an equivalent amount is used in processing and packaging of food. These two are, according to Mosely, 7 percent each of national energy use. And then another 3 percent of national energy consumption is used in food distribution.

Using these additional inputs, it turns out that in 2002 we used total energy of 4.13 quads as input for that 1.58 quads of caloric output. The cost now turns out to be 2.6 units of energy in for each unit of edible energy out.

Therefore it is absolutely true that we are eating energy in this modern day and age. This should make us very alert when we think about World Population. It has now reaching 7 billion—projected to reach 8 billion in 2050—a time by which we shall have pretty much consumed currently know hard reserves and only shale stuff will be left to take us to the next billion-person addition to the human family.

Added later. Thanks to russel’s comment to an earlier version of this post, I realized that I was using the wrong kinds of calories, not the kilo calories used in food. This post has therefore been updated to correct that very big error. I appreciate the correction.