the science and history of rapid climate change

Les Schaffer schaffer at optonline.net
Mon Aug 11 21:33:13 MDT 2003


The latest issue of Physics Today has an interesting article on the
history of scientific understanding of rapid global climate change,
written at a fairly lay level:

  http://www.physicstoday.org/vol-56/iss-8/p30.html

snippet quoted at end. The American Inst. of Physics (parent of
Physics Today) has a related web site entitled "The Discovery of
Global Warming":

  http://www.aip.org/history/climate/index.html

which includes further material on rapid change:

  http://www.aip.org/history/climate/rapid.htm

and relavant to the discussion with Jurriaan on complexity/chaos
theory, a section entitled "Chaos in the Atmosphere":

  http://www.aip.org/history/climate/chaos.htm

for example:

  The meteorological questions that had launched chaos theory remained
  among the hardest to answer. Some scientists now insisted that the
  climate system's intrinsic fluctuations would utterly defeat any
  attempt to calculate its changes. Thus the 1980 edition of one
  classic textbook said that predictions of greenhouse effect warming
  were dubious because of chaotic "autovariations." Lorenz and others
  argued that the recently observed global warming might be no
  evidence of a greenhouse effect or any other external influence, but
  only a chance excursion in the drunkard's random walk.(34)

  Most scientists agreed that climate has features of a chaotic
  system, but they did not think it was wholly unpredictable. To be
  sure, it was impossible to predict well in advance, with any
  computer that could ever be built in the actual universe, that a
  tornado would hit a particular town in Texas on a particular day
  (not because of one guilty butterfly, of course, but as the net
  result of countless tiny initial influences). Yet tornado seasons
  came on schedule. That type of consistency showed up in the
  supercomputer simulations constructed in the 1980s and after. Start
  a variety of model runs with different initial conditions, and they
  would show, like most calculations with complex nonlinear feedbacks,
  random variations in the weather patterns computed for one or
  another region and season. But their predictions for global average
  temperature usually remained within a fairly narrow range under
  given conditions. Critics replied that the computer models had been
  loaded with artificial assumptions in order to force them to produce
  regular-looking results. But gradually the most arbitrary
  assumptions were pared away. The models continued to reproduce, with
  increasing precision, many kinds of past changes, all the way back
  through the ice ages. As the computer work became more plausible, it
  set limits on the amount of variation that might be ascribed to pure
  chance.

in connection with rapid climate change is the popularized notion of
the "butterfly effect", which has been pretty badly mangled in its
application to climate prediction (see comment on tornado's in quote
above). more on this as discussion progresses.


les schaffer




----------------------------

 The Discovery of Rapid Climate Change

Only within the past decade have researchers warmed to the possibility
of abrupt shifts in Earth's climate. Sometimes, it takes a while to
see what one is not prepared to look for.

Spencer Weart


How fast can our planet's climate change? Too slowly for humans to
notice, according to the firm belief of most scientists through much
of the 20th century. Any shift of weather patterns, even the Dust Bowl
droughts that devastated the Great Plains in the 1930s, was seen as a
temporary local excursion. To be sure, the entire world climate could
change radically: The ice ages proved that. But common sense held that
such transformations could only creep in over tens of thousands of
years.

In the 1950s, a few scientists found evidence that some of the great
climate shifts in the past had taken only a few thousand years. During
the 1960s and 1970s, other lines of research made it plausible that
the global climate could shift radically within a few hundred
years. In the 1980s and 1990s, further studies reduced the scale to
the span of a single century. Today, there is evidence that severe
change can take less than a decade. A committee of the National
Academy of Sciences (NAS) has called this reorientation in the
thinking of scientists a veritable "paradigm shift." The new paradigm
of abrupt global climate change, the committee reported in 2002, "has
been well established by research over the last decade, but this new
thinking is little known and scarcely appreciated in the wider
community of natural and social scientists and policymakers."1

Much earlier in the 20th century, some specialists had evidence of
abrupt climate change in front of their eyes. The evidence was
meaningless to them. To appreciate change occurring within 10 years as
significant, scientists first had to accept the possibility of change
within 100 years. That, in turn, had to wait until they accepted the
1000-year time scale. The history of this evolution gives a good
example of the stepwise fashion in which science commonly proceeds,
contrary to the familiar heroic myths of discoveries springing forth
in an instant. The history also suggests why, as the NAS committee
worried, most people still fail to realize just how badly the world's
climate might misbehave.


full at: http://www.physicstoday.org/vol-56/iss-8/p30.html





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