By combining biological energetics with physical science units, one can show that the steady-state rate at which available work is captured by living things is a limited, but objective, indicator of the state of life on our planet. Its role might be similar to that played by the GDP (Gross Domestic Product) when it functions as an indicator of the state of an economy*. Of course, the life power stream involves our role in a budget that is balanced not by us, but by the laws of physics.
Concerning the resource impact of a given consumable, it allows us to calculate a single number in units of power stream time. For example, a hotdog without mustard or bun probably requires more than 50 nanoseconds of the full powerstream presently in use by life on our planet. Although any single number will have both advantages and pitfalls, in principle this is a number which tells us something tangible in a global context, even when it is not the most important thing to know.
* Some think that coins, currency, and the financial systems that have developed therefrom are in essence ritualized forms, in nature, of available work. After all, they only make sense if they obey a conservation law, and cannot be inexpensively replicated (e.g. by xeroxing) at will.
Other resources of possible interest: What does quantum mechanics look like in complex color? Comparing energies: Does food, gasoline, or electricity buy more for less? How about constant acceleration at anyspeed? deBroglie's electrons and some remarkable TEM facts. Try focussing a high-res electron microscope image on-line! Is statistical physics a dead subject, or is there another paradigm change afoot?
Physical energy, variously measured in joules, BTU's, Calories (kcal), megatons, ergs, kilowatt-hours and electron volts, is involved in many aspects of life on our planet. For example, plants and animals need energy to live and work, houses need energy for heating and for appliances, and cars need energy for locomotion. As you might guess from the list of unit names above, the inter-relationship between these various aspects is obscured by the specialized jargon for dealing with energy that has evolved independently in each. A table of common energies in various units might also be used to illustrate this point.
Physical power, defined as energy per unit time, is variously measured in watts (joules per second) and horsepower. Electric companies, used to delivering energy per unit time, have even chosen power multiplied by time (kilowatt-hours) for their unit of energy.
One approximate constant for life on our planet is also a power: the flux of solar energy per unit time incident on our planet in the form of electromagnetic radiation from the sun. This solar constant between 1017 and 1018 watts, has been and continues to be the major ongoing (i.e. steady-state) source of energy put to use by life on our planet.
If we consider only the arable land on earth (about a quarter of that 25% of the earth's surface area which is not ocean), and figure that plant life on that land converts about a 40th of the incident energy to calories in biomass (after the plant respiration losses requisite to that capture, cf. E. P. Odum, Fundamentals of Ecology, Saunders 1971), then the steady-state energy per unit time captured by life on our planet (the life power stream or "LPS" mentioned above, dominated by Odum's net primary productivity) is around 7×1017×(1/4)×(1/4)×(1/40)=1015 watts. Experts who've considered land and sea-based biomes more carefully, namely Vitousek et al. in Biosciences 36-6 (1986) 368-373, find a global photosynthetic productivity closer to 1.5×1014 watts, with about 60% of that land based. Until we have time to take this into account, our initial LPS value of 1015 watts will serve to illustrate its nature and some applications in the Tables below.
One thing to note quickly: Independent of its impact on species diversity and quality of life, conversion of a garden to a parking lot, or a rainforest to a desert, decreases the LPS by the fractional loss of ecological net primary productivity which ensues as a result. Although LPS indicators, like GNP indicators, are by no means everything, they therefore are an objective measure of a real feature of the state of life on our planet.
Rates at which energy is being used can be expressed in terms of the LPS for comparison. We've listed only a couple of entries so far. A look at the 1993 World Almanac (Scripps Howard Publishing) shows that the energy production/consumption they refer to is not that which goes directly through living things, but which is mined from the earth as fossil fuels and/or generated by hydroelectric or nuclear power plants. Except for the hydroelectric component, these are not part of the steady-state resource considered in the LPS, since they tap the "standing crop" of energy resources already in place on our planet. The authors seem unaware that the real primary producers of energy for life on earth are plants. Even though the energies they do consider are mostly from past accumulations rather than new acquisitions, the listed rates of fuel/electricity discovery and use still seem to constitute only a small fraction (e.g. a percent or so) of the primary energy production associated with the earth's biological LPS.
|one human being or a 100 watt bulb||100 watts||10-13|
|Guri (Raul Leoni) Hydro Plant, Venezuela||1010 watts||10-5|
|World Nuclear Power||3×1011 watts||0.0003|
|1990 Fuel/Electricity Consumption Worldwide||1013 watts||0.01|
Although our fuel/electricity sources are modest in comparison, our species is also a major consumer and modifier of the terrestrial photosynthetic productivity which comprises most of life's steady state power. For example, as was mentioned at a recent AABGA meeting in St. Louis, the 1986 article in Bioscience cited above estimates that humans are either consuming, wasting, or diverting about 40% of the land-based component of that photosynthetic productivity!
Suggestion of other quantities to list, and better researched and documented values for the ones already listed, in the tables here as well as in the text, would be of interest. We would be happy to link to and/or credit the original sources for improved values, if you are able to provide them to the e-mail address below.
Lastly, we note here that specific quantities of energy can be measured in terms of the time the present-day LPS would require to generate that energy. In other words, how long would a given resource allocation exclusively tie up the full machinery of life on earth?
The answer is not always obtained with a simple energy units conversion. Some forms of energy require a larger investment by the machinery of life on our planet than do others. For example, I gather from reading Odum (above) that animal biomass requires something like 100 times the primary production that one might infer from its caloric value alone. This is because a cow, for example, requires much more than its weight in grain to reach maturity. A carnivore's LPS need is accordingly larger than a vegetarian's, by the corresponding factor.
|a human or a 100 watt bulb for 1 hour||360000 joules||0.35 nanoseconds|
|Food energy in an apple (120kcal)||500000 joules||0.5 nanoseconds|
|Vegetarian's daily requirement (2100kcal)||9000000 joules||8 nanoseconds|
|Combustion energy in a gallon of gas||10^8 joules||100 nanoseconds|
|Carnivore's daily LPS needs (2100kcal*100)||9x10^8 joules||800 nanoseconds|
|Earth's gravity well for a person||4x10^9 joules||4 microseconds|
|Energy thermalized in 1 megaton explosion||4x10^15 joules||4 seconds|
|US daily fuel/electricity consumption||2x10^17 joules||4 minutes|
|Fossil fuel left on earth||2x10^23 joules||6 years|
Again, better-documented values for the entries here, and suggestion for other things to list, would be most welcome. For example, better values for the LPS and fossil-fuel resources needed for various consumables (including hamburgers, french fries, and gasoline for example) might provide the basis for a "used-resource" labelling program for consumables to increase consumer awareness of their impact on the world in which we live!
Note: A nanosecond (one billionth of a second) is the time it takes light to travel approximately one foot.
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