From: SCHLOERER@rzmain.rz.uni-ulm.de (Jan Schloerer)
Subject: Re: Historic levels of methane by bison (was Re: Perot ad an
Organization: University of Ulm, Germany
Date: Thu, 5 Nov 1992 12:17:58 GMT
X-News-Reader: VMS NEWS 1.24

  Topics:  Global environmental engineering
           What to do about methane ?
           Methane sources and sinks
---------------------------------------------


Several posts in this thread explored :

   *  Might so-called 'technological fixes' to the atmosphere,
      in some cases, become necessary as a last resort ?

   *  What to do about methane in the atmosphere ?


For the first issue, some researchers think: maybe.  Ralph Cicerone,
Scott Elliott and Richard Turco, who are investigating a concept to
close the ozone hole, recently summarized their thoughts on  "global
environmental engineering"  (Nature 356, 9 April 1992, 472).
Some of the gist:

   For an effective debate, publication of ideas in peer-reviewed
   journals and peer-review of research plans is essential.  Detailed
   feasibility studies should wait until the underlying scientific
   consensus is documented as well as reviewed critically and repeatedly.
   Analyses of engineering costs or of timetables are premature at this
   stage.  Ideas for global environmental engineering are likely to be
   badly flawed technically, and will be seen to be so through review
   ...  We hope that ideas will spur research as they expose weaknesses
   in our understanding of the Earth system ...

   Social, ethical and legal questions will surround any serious proposal
   for global environmental engineering.  Incomplete understanding almost
   always characterizes the behaviour of environmental systems ...
   Without understanding the mechanics of a natural system, there is
   little basis for predicting the system's response to perturbations.
   Accordingly, risks are inherent in any large-scale intervention   -
   risks of unanticipated side-effects, of wasting time and resources,
   or of diverting attention from the root causes of environmental
   problems.

   Who must make decisions and with what criteria ?  ...  In any case,
   we believe that international, but nongovernmental, bodies of
   scientists must be involved in the initial evaluations.  Political
   judgements will also be required to express differing values and
   perceptions of risks  -  for example, those most threatened by
   inaction might press for intervention long before others would be
   receptive to such ideas.

   We hope to stimulate debate and scientific research on these issues
   ... Their complexity could demand decades for significant progress.
   In the meantime we must address the underlying causes of environmental
   problems, if only to buy more time for us to understand the Earth
   as a system and the consequences of human interactions with it.
   

As to the methane issue, I believe that, for the time being, it would
hardly qualify as a promising or urgent candidate for 'fixes to the
atmosphere'.  There are several reasons :

-  The rate of increase of atmospheric methane seems to have decreased 
   during the 1980s.  Of course, this may change again in the future.
   The slowdown is likely to originate in the latitude band 30-90
   degrees N, its reasons are not understood.    (L.P.Steele et al,
   Nature 358, 23 July 1992, 313-316)

-  The 'responses' Working Group III of the Intergovernmental Panel on
   Climate Change (IPCC), for one, claims:  "Technological options are
   available for limiting emissions from the major  [anthropogenic]
   sources, other than flooded rice cultivation and biomass burning.
   These options may be economically viable at suitable locations in
   many regions of the world, and represent different levels of technical
   and capital needs."    (1992 IPCC Supplement, short version, p 45-46.
   World Meteorological Organiz., Case Postale 2300, CH-1211 Gene`ve 2)

-  The present understanding of tropospheric chemistry is unsatisfactory,
   to say the least.  Just one example:  OH  plays a central role in
   tropospheric chemistry, among many others it is involved in methane
   oxidation.  The 'climate' Working Group I of the IPCC deplores that
   there are no direct measurements of OH which can give reliable
   information on the global distribution or changes over time.  There
   are attempts at indirect measurement, but presently it seems not even
   clear whether OH is increasing or decreasing globally.  A recent
   estimate based on a simple tropospheric box model deduced a trend
   of  +1.0 % +- 0.8 %  over the past decade, but this is hardly a
   definitive result.  (Climate Change 1992  -  The Supplementary Report
   to the IPCC Scientific Assessment, J. Houghton et al, eds, Cambridge
   Univ. Press 1992, p 60).


Finally, for those interested, some recent estimates of sources and sinks
of methane (CH4.  Same source, p 35).  Asterisk  *  indicates revised
estimate since IPCC 1990; the asterisk for the atmospheric increase is
missing in the report.  Low and high estimates are given in brackets.
Note that the totals of the best estimates are not entirely consistent.

                                              Teragrams CH4 per year
Natural sources
   Wetlands                                      115   (100-200) 
   Termites                                       20   ( 10- 50)   *
   Ocean                                          10   (  5- 20)
   Freshwater                                      5   (  1- 25)
   CH4 hydrate                                     5   (  0-  5)

Anthropogenic sources  (includes agriculture)
   Coal mining, natural gas & petr. industry     100   ( 70-120)   *
   Rice paddies                                   60   ( 20-150)   *
   Enteric fermentation                           80   ( 65-100)
   Animal wastes                                  25   ( 20- 30)   *
   Domestic sewage treatment                      25       ?       *
   Landfills                                      30   ( 20- 70)   *
   Biomass burning                                40   ( 20- 80)

Sinks
   Atmospheric  (tropospheric + stratospheric)
      removal                                    470   (420-520)   *
   Removal by soils                               30   ( 15- 45)
   Atmospheric increase                           32   ( 28- 37)  [*]


Jan Schloerer          schloerer@rzmain.rz.uni-ulm.de
Klinische Dokumentation           Uni Ulm
Postfach 3880     DW-7900 Ulm     Germany