 |
Bad Mileage - 98 tons of plants per gallon
October 27, 2003
Study shows vast amounts of 'buried sunshine' needed to fuel society
A staggering 98 tons of prehistoric, buried plant material - that's 196,000 pounds - is required to produce each gallon of gasoline we burn in our cars, SUVs, trucks and other vehicles, according to a study conducted at the University of Utah.
"Can you imagine loading 40 acres worth of wheat - stalks, roots and all - into the tank of your car or SUV every 20 miles?" asks ecologist Jeff Dukes, whose study will be published in the November issue of the journal Climatic Change.
But that's how much ancient plant matter had to be buried millions of years ago and converted by pressure, heat and time into oil to produce one gallon of gas, Dukes concluded.
Dukes also calculated that the amount of fossil fuel burned in a single year - 1997 was used in the study - totals 97 million billion pounds of carbon, which is equivalent to more than 400 times "all the plant matter that grows in the world in a year," including vast amounts of microscopic plant life in the oceans.
"Every day, people are using the fossil fuel equivalent of all the plant matter that grows on land and in the oceans over the course of a whole year," he adds.
In another calcultation, Dukes determined that "the amount of plants that went into the fossil fuels we burned since the Industrial Revolution began [in 1751] is equal to all the plants grown on Earth over 13,300 years."
Explaining why he conducted the study, Dukes wrote: "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)."
The study is titled "Burning Buried Sunshine: Human Consumption of Ancient Solar Energy." In it, Dukes conducted numerous calculations to determine how much plant matter buried millions of years ago was required to produce the oil, natural gas and coal consumed by modern society, which obtains 83 percent of its energy needs from fossil fuels.
"Fossil fuels developed from ancient deposits of organic material, and thus can be thought of as a vast store of solar energy" that was converted into plant matter by photosynthesis, he explains. "Using published biological, geochemical and industrial data, I estimated the amount of photosynthetically fixed and stored [by ancient plants] carbon that was required to form the coal, oil and gas that we are burning today."
Dukes conducted the study while working as a postdoctoral fellow in biology at the University of Utah. He now works for the Carnegie Institution of Washington's Department of Global Ecology on the campus of Stanford University in California.
How the calculations were done
To determine how much ancient plant matter it took to eventually produce modern fossil fuels, Dukes calculated how much of the carbon in the original vegetation was lost during each stage of the multiple-step processes that create oil, gas and coal.
He looked at the proportion of fossil fuel reserves derived from different ancient environments: coal that formed when ancient plants rotted in peat swamps; oil from tiny floating plants called phytoplankton that were deposited on ancient seafloors, river deltas and lakebeds; and natural gas from those and other prehistoric environments. Then he examined the efficiency at which prehistoric plants were converted by heat, pressure and time into peat or other carbon-rich sediments.
Next, Dukes analyzed the efficiency with which carbon-rich sediments were converted to coal, oil and natural gas. Then he studied the efficiency of extracting such deposits. During each of the above steps, he based his calculations on previously published studies.
The calculations showed that roughly one-eleventh of the carbon in the plants deposited in peat bogs ends up as coal, and that only one-10,750th of the carbon in plants deposited on ancient seafloors, deltas and lakebeds ends up as oil and natural gas.
Dukes then used these "recovery factors" to estimate how much ancient plant matter was needed to produce a given amount of fossil fuel. Dukes considers his calculations good estimates based on available data, but says that because fossil fuels were formed under a wide range of environmental conditions, each estimate is subject to a wide range of uncertainty.
Plants in your tank?
Dukes calculated ancient plant matter needed for a gallon of gasoline in metric units:
* One gallon of oil weighs 3.26 kilograms. A gallon of oil produces up to 0.67 gallons of gasoline. So 3.26 kilograms for a gallon of oil divided by 0.67 gallons means that at least 4.87 kilograms of oil are needed to make a gallon of gasoline.
* Oil is 85 percent carbon, so 0.85 times 4.87 kilograms equals 4.14 kilograms of carbon in the oil used to make a gallon of gasoline.
* Since only about one-10,750th of the original carbon in ancient plant material actually ends up as oil, multiply 4.14 kilograms by 10,750 to get roughly 44,500 kilograms of carbon in ancient plant matter to make a gallon of gas.
* About half of plant matter is carbon, so double the 44,500 kilograms to get 89,000 kilograms - or 89 metric tons - of ancient plant matter to make a gallon of gas. In U.S. units, that is equal to a bit more than 196,000 pounds or 98 tons.
Dukes made similar calculations for oil, natural gas and coal to determine that it took 44 million billion kilograms (97 million billion pounds) of carbon in ancient plant matter to produce all the fossil fuel used in 1997. That includes 29 million billion kilograms of prehistoric plants to produce a year's worth of oil (including gasoline), almost 15 million billion kilograms of buried plant matter to make all the natural gas used in 1997, and 27,000 billion kilograms of dead plants to produce all the coal used in the same year.
"It took an incredible amount of plant matter to generate the fossil fuels we are using today," says Dukes. "The new contribution of this research is to enable us to picture just how inefficient and unsustainable fossil fuels are - inefficient in terms of the conversion of the original solar energy to fossil fuels. Fortunately, it is much more efficient to use modern energy sources like wind and solar. As the reasons keep piling up to switch away from fossil fuels, it is important that we develop these modern power sources as quickly as possible."
What about modern plant biomass?
Unlike the inefficiency of converting ancient plants to oil, natural gas and coal, modern plant "biomass" can provide energy more efficiently, either by burning it or converting into fuels like ethanol. So Dukes analyzed how much modern plant matter it would take to replace society's current consumption of fossil fuels.
He began with a United Nations estimate that the total energy content of all coal, oil and natural gas used worldwide in 1997 equaled 315,271 million billion joules (a unit of energy). He divided that by the typical value of heat produced when wood is burned: 20,000 joules per gram of dry wood. The result is that fossil fuel consumption in 1997 equaled the energy in 15.8 trillion kilograms of wood. Dukes multiplied that by 45 percent - the proportion of carbon in plant material - to calculate that fossil fuel consumption in 1997 equaled the energy in 7.1 trillion kilograms of carbon in plant matter.
Studies have estimated that all land plants today contain 56.4 trillion kilograms of carbon, but only 56 percent of that is above ground and could be harvested. So excluding roots, land plants thus contain 56 percent times 56.4, or 31.6 trillion kilograms of carbon.
Dukes then divided the 1997 fossil fuel use equivalent of 7.1 trillion kilograms of carbon in plant matter by 31.6 trillion kilograms now available in plants. He found we would need to harvest 22 percent of all land plants just to equal the fossil fuel energy used in 1997 - about a 50 percent increase over the amount of plants now removed or paved over each year.
"Relying totally on biomass for our power - using crop residues and quick-growing forests as fuel sources - would force us to dedicate a huge part of the landscape to growing these fuels," Dukes says. "It would have major environmental consequences. We would have to choose between our rain forests and our vehicles and appliances. Biomass burning can be part of the solution if we use agricultural wastes, but other technologies have to be a major part of the solution as well - things like wind and solar power."
University of Utah
 | Petrostate: Putin, Power, and the New Russia by Marshall I. Goldman In the aftermath of the financial collapse of August 1998, it looked as if Russia's day as a superpower had come and gone. That it should recover and reassert itself after less than a decade is nothing short of an economic and political miracle. Based on extensive research, including several interviews with Vladimir Putin, this revealing book chronicles Russia's dramatic reemergence on the... |
 | Rising Powers, Shrinking Planet: The New Geopolitics of Energy by Michael T. Klare From the author of the now-classic Resource Wars, an indispensable account of how the world’s diminishing sources of energy are radically changing the international balance of power Recently, an unprecedented Chinese attempt to acquire the major American energy firm Unocal was blocked by Congress amidst hysterical warnings of a Communist threat. But the political grandstanding missed a... |
 | Gusher of Lies: The Dangerous Delusions of Energy Independence by Robert Bryce Everybody is talking about "energy independence." But is it really achievable? Is it actually even desirable? In this controversial, meticulously researched book, Robert Bryce exposes the false promises behind the rhetoric while blasting nearly everybody— Republicans, Democrats, environmentalists, and war-mongering neoconservatives—for misleading voters about our energy needs. ... |
 | The Party's Over: Oil, War and the Fate of Industrial Societies by Richard Heinberg The world is about to run out of cheap oil and change dramatically. Within the next few years, global production will peak. Thereafter, even if industrial societies begin to switch to alternative energy sources, they will have less net energy each year to do all the work essential to the survival of complex societies. We are entering a new era, as different from the industrial era as the latter... |
 | The Long Emergency: Surviving the Converging Catastrophes of the Twenty-First Century by James Howard Kunstler With his classics of social commentary The Geography of Nowhere and Home from Nowhere, James Howard Kunstler has established himself as one of the great commentators on American space and place. Now, with The Long Emergency, he offers a shocking vision of a post-oil future. As a result of artificially cheap fossil-fuel energy, we have developed global models of industry, commerce, food... |
 | The Carbon-Free Home: 36 Remodeling Projects to Help Kick the Fossil-Fuel Habit by Stephen & Rebekah Hren You've read the stories and watched the documentaries. So you're convinced--burning fossil fuels leads to global climate change; supplies of fossil fuels are diminishing in quantity and increasing in price. You've fretted and worried, but still go through your day consuming some quantity of non-renewable fossil fuels to accomplish nearly every task (and you may not even realize it). You want to... |
 | The Deep Hot Biosphere : The Myth of Fossil Fuels by Thomas Gold Suppose someone claimed that we are not running out of petroleum? Or that life on Earth began below the surface of our planet? Or that oil and gas are not "fossil fuels"? Or that if we find extraterrestrial life it is likely to be within, not on, other planets? You might expect to hear statements like these from an author of science fiction. But what if they came from a renowned physicist, an... |
 | Eating Fossil Fuels: Oil, Food and the Coming Crisis in Agriculture by Dale Allen Pfeiffer The miracle of the Green Revolution was made possible by cheap fossil fuels to supply crops with artificial fertilizer, pesticides, and irrigation. Estimates of the net energy balance of agriculture in the United States show that ten calories of hydrocarbon energy are required to produce one calorie of food. Such an imbalance cannot continue in a world of diminishing hydrocarbon resources. ... |
 | Energy: Physical, Environmental, and Social Impact (3rd Edition) by Gordon J. Aubrecht This book focuses on energy needs, trends, and long-term prospects and resource supplies. It discusses the physics of energy, atoms, nuclei, thermal energy, solar energy, alternative energy, and the consequences of energy production. For physicists, geologists, and geographers, or anyone who wants a better understanding of the production, consumption, and conservation of... |
 | Sustainable Fossil Fuels: The Unusual Suspect in the Quest for Clean and Enduring Energy by Mark Jaccard More and more people believe we must quickly wean ourselves from fossil fuels - oil, natural gas and coal - to save the planet from environmental catastrophe, wars and economic collapse. Professor Jaccard argues that this view is misguided. We have the technological capability to use fossil fuels without emitting climate-threatening greenhouse gases or other pollutants. The transition from... |
| © 2008 BrightSurf.com |