[THS] Alternative Fuels? Green energy sources?

[The Harder Stuff in news and commentary]

The BP atrocity is igniting much renewed interest in alternative energy sources, to replace or at least drastically reduce our dependence on petroleum. Is this possible in practice? Not if it is impossible in principle. 

Our current rate of petroleum use is impossible to replace: "The fossil fuels burned in 1997 were created from organic matter ... >400 times the net primary productivity (NPP) of the planet’s current biota." What does this mean for the future? You figure it out.   - TheHarderStuff (indeed)

[article snipped, read the entire analysis at the url]

BURNING BURIED SUNSHINE: 
HUMAN CONSUMPTION OF ANCIENT SOLAR ENERGY

http://globalecology.stanford.edu/DGE/Dukes/Dukes_ClimChange1.pdf

BURNING BURIED SUNSHINE: 
HUMAN CONSUMPTION OF ANCIENT SOLAR ENERGY 
JEFFREY S. DUKES* Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112-0840, U.S.A. E-mail: dukes at globalecology.stanford.edu *Now at: Carnegie Institution of Washington, Department of Global Ecology, 260 Panama St., Stanford, CA, 94305-1297, U.S.A. Climatic Change 61: 31–44, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands.

 Abstract. 

Fossil fuels developed from ancient deposits of organic material, and thus can be thought of as a vast store of solar energy from which society meets >80% of its current energy needs. Here, using published biological, geochemical, and industrial data, I estimate the amount of photosynthetically fixed and stored carbon that was required to form the coal, oil, and gas that we are burning today. Today’s average U.S. Gallon (3.8 L) of gasoline required approximately 90 metric tons of ancient plant matter as precursor material. The fossil fuels burned in 1997 were created from organic matter containing 44 × 1018 g C, which is >400 times the net primary productivity (NPP) of the planet’s current biota. As stores of ancient solar energy decline, humans are likely to use an increasing share of modern solar resources. I conservatively estimate that replacing the energy humans derive from fossil fuels with energy from modern biomass would require 22% of terrestrial NPP, increasing the human appropriation of this resource by ~50%.

1. Introduction

Fossil fuel consumption is widely recognized as unsustainable. However, there has been no attempt to calculate the amount of energy that was required to generate fossil fuels (one way to quantify the ‘unsustainability’ of societal energy use), and discussion about the consequences of replacing fossil fuels with modern solar energy has been limited (but see Cook et al., 1991; Hall et al., 1991; Giampietro et al., 1997). Recent attempts to estimate the sustainability of human activities have taken a variety of approaches. Some researchers have estimated the amount of photosynthetic energy (in the form of NPP) that is appropriated by humans (Vitousek et al., 1986; Rojstaczer et al., 2001). Others have estimated the ‘ecological footprint’ of humanity, the amount of biologically productive space necessary to sustain human consumption (Wackernagel et al., 2002). Neither of these approaches takes into account the sustainability of fossil fuel consumption. The NPP approach focuses entirely on consumption and reduction of the potential photosynthetic energy captured in modern times, ignoring energy acquired through fossil fuel consumption. The ecological footprint approach usually accounts for fossil fuel burning by designating land for use in climate stabilization. This land would theoretically prevent greenhouse gas buildup by recapturing fossil fuel carbon that has entered the atmosphere (Wackernagel et al., 1999; Ferng, 2002). While this approach compensates for the climate effects of fossil fuel burning, it does not replenish the original store of energy. Rarely, footprint analyses account for fossil energy use by calculating the amount of land required to grow biomass or biofuels that could act as energy substitutes for fossil fuels. This replacement approach often leads to larger footprints than the climate stabilization approach (Wackernagel et al., 2002). True analyses of sustainability must take into account the land or NPP needed to replace the stored energy that we use.

Here, I have compiled data on: (1) the proportion of fossil fuel reserves derived from different environments (i.e., terrestrial vs. marine vs. lacustrine), (2) the efficiency with which photosynthetic organisms are converted to peat or carbonrich sediment in these environments, (3) the efficiency with which organic deposits were converted to fossil fuels, and (4) the efficiency with which we are able to retrieve fossil fuels from near the earth’s surface. From these data, I calculate the amount of paleoproductivity that was needed to create fossil fuels. I also estimate the amount of solar energy consumed by humans in the form of fossil fuels, compare the solar efficiency of fossil fuels to that of more modern sources of solar-derived energy, and estimate the minimum amount of modern photosynthetic product necessary to replace fossil fuel energy.

<snip - complete pdf at url above]