Re: Declining water and oil

From: Steven M Smith (smsmith@usgs.gov)
Date: Thu Nov 13 2003 - 12:48:38 EST

  • Next message: Roger Olson: "Re: Declining water and oil"

    After skimming several posts on this ASA thread I ran across the following
    web article from SpaceDaily.com which addresses several of the issues under
    discussion. I'll just include a few 'teasers' here. You can read this
    popular account of the study at
    <http://www.spacedaily.com/news/energy-tech-03zp.html>

    <<Ninety Eight Tons Of Primordial Plant Matter Per Gallon
    Salt Lake City - Oct 27, 2003

    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.>>

    [Snip]

    <<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.>>

    [Snip]

    <<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.>>

    [Snip]

    <<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....>>

    Nothing was said in the SpaceDaily.com article about the energy costs
    needed to grow and harvest 22% of all land plants. The article concludes:

    <<"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.">>

    _____________
     Steven M. Smith, Geologist, U.S. Geological Survey
     Box 25046, M.S. 973, DFC, Denver, CO 80225
     Office: (303)236-1192, Fax: (303)236-3200
     Email: smsmith@usgs.gov
     -USGS Nat'l Geochem. Database NURE HSSR Web Site-
      http://pubs.usgs.gov/of/1997/ofr-97-0492/



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