🚀 go-pugleaf

In article <1992Dec30.161445.12236@unocal.com>, stgprao@st.unocal.COM (Richard Ottolini) writes:
> In article <JMC.92Dec29211051@SAIL.Stanford.EDU> jmc@cs.Stanford.EDU writes:
> >from a U.P. story
> >
> >	     WASHINGTON (UPI) -- Life on Earth as we know it will
> >     come to an end in 1,500 million years and the planet will
> >     look more like its dusty, volcanic sister Venus in 2,500
> >     million years, scientists said Wednesday.
> 
> If we can't model the weather more than 5 days in advance nor agree on
> climate prediction in 50 years, who would have any confidence in this
> speculation?

-- 
1>  This has nothing to do with modelling weather.   The difficulty
in weather prediction is that the kinds of dynamical systems being
modelled are too sensitive to small changes in initial conditions
for the models to be accurate over long periods of time.

2>  Climate models are in fact much more accurate than weather
models.   This is because they are concerned with average phenomena
and averages have much greater stability and predicitability.
Differences about climate models' prediction of global warming by
those who have studied such things are of the order of magnitude
of whether warming will be a bit over 1 degree C or two
or three times as high and whether it will take 50 years or 100
years.  There is a very substantial amount agreement.
This fact has been obscured by the intense ideological
disputes over the issue.

3>  The predictions of the ultimate history of the earth are based
on models of stars which are really fairly simple.  If the
sun warms up, it is probably not too far out to suggest possible
physical responses here on earth over long periods of time.  This
doesn't even require computer models.  Of course, none of this
can be certain, but remember that we are
talking about periods of hundreds of millions of years.   The
estimate of 1.5 billion is the largest I have seen.   The most
recent news article that I saw suggested that a previous estimate
of 100 million years was too low and that it might be more like
900 million years.  Clearly this analysis is all fairly new
and the arguments will be subject to intense scrutiny.  However,
I don't see why a consensus couldn't develop on the
matter among geophysicists.  This should be just a reliable and
scientific as beliefs now held about the early universe or other
events in deep space or deep time.  
  
4>  Except as interesting speculation, why should anyone care?
Remember that  the real (plentiful) fossil record on earth is only about
500 million years old.   Surely no one should worry seriously about
what sort of actions humanity should take to deal with such a problem.
Unfortunately, this may confuse people about the issue of global
warming which is something which may radically affect human societies
in the next several generations and which we may be able to do
something about.

Leonard Evens      len@math.nwu.edu      708-491-5537
Dept. of Mathematics, Northwestern Univ., Evanston, IL 60208