Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!mhuxv!mhuxf!mhuxm!mhuxn!ihnp4!gargoyle!carnes
From: carnes@gargoyle.UUCP (Richard Carnes)
Newsgroups: net.sci
Subject: Re: A Modest Proposal
Message-ID: <562@gargoyle.UUCP>
Date: Mon, 15-Sep-86 19:41:37 EDT
Article-I.D.: gargoyle.562
Posted: Mon Sep 15 19:41:37 1986
Date-Received: Sat, 27-Sep-86 09:29:19 EDT
References: <7197@sun.uucp>
Reply-To: carnes@gargoyle.UUCP (Richard Carnes)
Organization: U. of Chicago, Computer Science Dept.
Lines: 107
Summary: Measuring human impact on the environment

>>[Jan Wasilewsky]
>[Bob Hartman]

>>The premise is wrong: human population does not loom as large
>>vis-a-vis the rest of creation as some of its members believe. If
>>all the 5 billion of us were drowned in the Great Lakes, how much
>>would the water level rise? A fraction of an inch.
>
>This is true, but it's an improper measure.  It's not the combined
>volume of our bodies, but annual volume of food, fiber and fuel we
>consume that are the limiting factors, along with the capacity of the
>ecosystem to recycle our byproducts.

Yes, obviously it's what humans do, not their volume or weight, that
determines human impact on the environment.  Here is one way in which
this impact occurs:  in general, more people ==> more land used and
altered by people (particularly for agriculture) ==> more destruction
of plant and animal habitats ==> more extinctions of species and
(almost equally important) genetically diverse populations of species
==> in numerous ways an impoverished existence for humanity.

Here is a more precise way of calculating human impact on the
environment.  The following is excerpted from an article by P.M.
Vitousek et al., "Human appropriation of the products of
photosynthesis", *BioScience* 36: 368-373 (1986):

  *Homo sapiens* is only one of perhaps 5-30 million animal species on
  Earth, yet it controls a disproportionate share of the planet's
  resources.  Evidence of human influence is everywhere:  land-use
  patterns are readily visible from space, and the concentrations of
  carbon dioxide, methane, nitrous oxide, and other trace gases in the
  atmosphere are increasing as a consequence of human activities.
  Human beings are mobilizing a wide array of minerals at rates that
  rival or exceed geological rates.
  
  We examined human impact on the biosphere by calculating the fraction
  of net primary production (NPP) that humans have appropriated.  NPP
  is the amount of energy left after subtracting the respiration of
  primary producers (mostly plants) from the total amount of energy
  (mostly solar) that is fixed biologically.  NPP provides the basis
  for maintenance, growth, and reproduction of all heterotrophs
  (consumers and decomposers); it is the total food resource on Earth.
  We are interested in human use of this resource both for what it
  implies for other species, which must use the leftovers, and for what
  it could imply about limits to the number of people the earth can
  support.  ...
  
  We calculated human influences in three ways.  Our low estimate is
  simply the amount of NPP people use directly -- as food, fuel, fiber,
  or timber.  Our intermediate estimate includes all the productivity
  of lands devoted entirely to human activities (such as the NPP of
  croplands, as opposed to the proportion of crops actually eaten).  We
  also include here the energy human activity consumes, such as in
  setting fires to clear land.  Our high estimate further includes
  productive capacity lost as a result of converting open land to
  cities and forests to pastures or because of desertification or
  overuse (overgrazing, excessive erosion).  The high estimate seems a
  reasonable statement of human impact on the biosphere. ...
  
  ...[H]umans now appropriate nearly 40% of potential terrestrial
  productivity, or 25% of the potential global terrestrial and aquatic
  NPP. ... Furthermore, humans also affect much of the other 60% of
  terrestrial NPP, often heavily. ...
  
  ...[W]e believe some reasonable conclusions can be drawn from these
  estimates.
  
  First, human use of marine productivity is relatively small.
  Although even this low level may not be sustainable [see *Global
  2000* Report to the President], it is unlikely to prove broadly
  catastrophic for oceanic ecosystems. ...
  
  On land the situation appears very different.  We estimate that
  organic material equivalent to about 40% of the present net primary
  production in terrestrial ecosystems is being co-opted by human
  beings each year.  People use this material directly or indirectly,
  it flows to different [nonhuman] consumers and decomposers than it
  otherwise would, or it is lost because of human-caused changes in
  land use.  People and associated organisms use this organic material
  largely, but not entirely, at human direction, and the vast majority
  of other species must subsist on the remainder.  An equivalent
  concentration of resources into one species and its satellites has
  probably not occurred since land plants first diversified.
  
  The co-option, diversion, and destruction of these terrestrial
  resources clearly contributes to human-caused extinctions of species
  and genetically distinct populations -- extinctions that could cause
  a greater reduction in organic diversity than occurred at the
  Cretaceous-Tertiary boundary 65 million years ago.  This decimation
  of biotic resources will foreclose numerous options for humanity
  because of the loss of potentially useful species and the genetic
  impoverishment of others that may survive.
  
  The information presented here cannot be used directly to calculate
  the Earth's long-term carrying capacity for human beings because,
  among other things, carrying capacity depends on both the affluence
  of the population being supported and the technologies supporting it.
  But our results do indicate that with *current* patterns of
  exploitation, distribution, and consumption, a substantially larger
  human population -- half again its present size or more -- could not
  be supported without co-opting well over half of terrestrial NPP.
  Demographic projections based on today's population structures and
  growth rates point to at least that large an increase within a few
  decades and a considerable expansion beyond that. ... [Vitousek et
  al.]

Richard Carnes