Constructed Climates

Figure 3.1: Sources of energy used in the United States over the last 200 years. The table shows each source’s 2008 contribution to total energy use. Domestically produced petroleum has dropped off lately, but imports have made up the difference (our biggest single supplier being Canada, with Mexico a close second). Domestically, coal and natural gas substitute, in part, for decreasing petroleum supplies. Renewable sources have a long way to go to replace the top four fossil-fuel sources. (data from Annual Energy Review 2008, U.S. Department of Energy.) Note that a quadrillion equals a thousand million million, or, in scientific notation, 10¹⁵.

America’s energy demands increased and its energy sources changed over the last two centuries (Figure 3.1). One hundred years ago, all we used was wood and coal.[1] Once industrialization started, coal became our major source.[2] Petroleum and natural gas, with their high energy content (see Figure 3.16), quickly overtook coal, but as those domestic sources become depleted, petroleum imports have made up the loss, and coal once again dominates our domestic energy sources. At present, geothermal, wind, and solar make roughly no contribution.[3] And as we consider retreating back to biofuels, I later discuss extensively the potential contribution of trees to energy use in Figure 3.16.

Keep in mind that we won’t run out of fossil-fuel-based energy anytime soon. The Energy Information Administration (EIA), the official energy statistics supplier of the United States, reports a use of about 1 billion tons of coal per year, with reserves estimated at about 270 billion tons in the United States, and 1,000 billion tons worldwide.[4] Those numbers mean several hundred years’ worth of coal to burn, about four times as much as Americans have used over the last century, and lots more fossil-carbon emissions. The EIA also reports a world daily consumption of 83 million barrels of liquid fuels, and total worldwide petroleum reserves as just 1.3 trillion barrels, about 10 years’ worth at 100 billion barrels used per year.[5] As dire as that sounds for 20 years hence, many countries invest only enough money in finding reserves to maintain a 10-year horizon.

Averaged over the last century, roughly speaking, all these energy sources add up to 30–50 quadrillion (10¹⁵) Btus per year, with present levels at 100 quads per year.[6] Here’s an interesting calculation. The United States, including Alaska,[7] covers about 10 million square kilometers, or 10¹³ square meters. Thus, America’s annual energy use in 2008 averages about 10,000 Btus/m². For comparison, averaged over the entire United States, vegetation has a net primary productivity that works out to maybe 6,000 Btus/m² (see the rough calculations discussed in Figure 3.17)![8] Annually, we use nearly twice the energy that all our plants fix in their tissue. Even the 2008 use of 3.9 quads of wood and biomass energy works out to 390 Btus/m² each year, more than 5% of the biosphere’s annual net primary productivity, but just 3% of our total energy demand. Our use also reduces the availability of plant material to other nonhuman consumers. Most of the atmospheric carbon dioxide fixed by plants feeds into future respiration by other organisms, like bacteria, fungi, and herbivores, that use the energy contained in plant matter and release the CO₂ back into the atmosphere. Using biomass for energy cuts back their consumption. It is a simple fact that biomass will never satisfy our present energy use.

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[1]Shafik and Bandyopadhya (1992) discuss income and environmental quality. Measured over global scales, increasing per capita income generally shows an initial deterioration in many environmental quality indicators, but with further increasing income, most indicators show increasing environmental quality. Perhaps this relationship reflects a use of wood as a primary energy source in developing countries, and transitioning out of biomass fuels as they develop.

[2]Before 1950, the human emissions signature was observable in a diluted C₁₄ to C₁₂ ratio, but atmospheric nuclear weapons testing obliterated that signal by putting tremendous amounts of radioactive carbon into the atmosphere. These topics are covered by Druffel et al. (2001) and Levin and Hesshaimer (2000). This dilution is called the “Seuss effect.”

[3]Energy source data come from the Annual Energy Review 2006, along with 2007 and 2008 numbers from the 2008 publication, produced by U.S. Department of Energy, Energy Information Administration DOE/EIA-0384. This publication provides a huge amount of fascinating information.

[4]Data on coal use and reserves are found on the U.S. Energy Information Administration website. They report both 1,000 million tons of coal per year and 23.79 x 10¹⁵ Btu of coal energy obtained: Simple division yields about 6,000 Btu/kg coal. (This number doesn’t quite match up with numbers I present in Figure 3.16, which show 14,000 Btu/kg of wood, and with my statement that one unit of coal equals 1.59 units of wood. I have not yet resolved the discrepancy.) Their curves then represent our coal use over the last century as roughly 600 million tons of coal per year, or 60,000 million tons. U.S. coal reserves are estimated at 270,000 million tons-a few more centuries to burn, if we can stand the heat.

[5]Energy consumption statistics can be found at www.eia.doe.gov/oiaf/ieo/oil.html. Additional information can be found in the British Petroleum Statistical Review of World Energy 2008, at www.bp.com.

[6]To get some idea of our total energy use from domestic sources, let’s just multiply rough averages for each of these annual energy use values by another rough estimate of how long each has been used. Looking at these curves, I estimate coal use as 15 quads for 100 years, petroleum use as 15 quads for 60 years, and natural gas use as 18 quads for 50 years. These numbers total 3,300 quadrillion Btus, and for further simplicity, let’s say it was used evenly over the last 100 years, giving a rough value for the United States’ energy use as 30 quadrillion Btus per year. Regarding my estimate of U.S. energy use as 30 quadrillion Btus per year, never mind that recent levels are more than 50 quads/year: In an order-of-magnitude calculation, 30 equals 50.

[7]Alaska’s 1.7 million km2 and 700,000 people really skew per capita calculations, for better or worse, with few people and lots of area (520 acres per person). Per capita perspectives of Canada, for example, would be very different from those of the 48 U.S. states.

[8]Average net primary productivity over the entire United States equals about 400 grams of carbon per square meter, and I use a conversion of about 14,000 Btus per kilogram of wood. Dukes (2003) provides some additional, independent connections between different fuel sources, including energy retention of NPP when fossil fuels form, and reports an energy content of plant material of 19,000 Btus/kg. Be warned: Other than this difference, I haven’t checked my numbers against his results, either in this section or the others, so some discrepancies are likely.