🚀 go-pugleaf

In article <789@spdcc.COM> eli@spdcc.COM (Steve Elias) writes:
>>> eli@spdcc.COM (Steve Elias)

::And in thinking about this, it is well to remember that the sun is,
::itself, about 3% variable, so that a small hicup in solar activity could
::swamp this effect for another 300 years at least.

:	could Wayne or anyone elaborate on this??  i'm under the impression
:	that the hiccups he refers to are sun-spots.  they affect the solar
:	wind, but not the radiated EM energy from the sun, as far as i know.
:	does anyone have more information on this?  
:
:	what is the predicted effect if the radiated energy from the sun
:	did rise by 3% for a few hundred or thousand years??  
:
:	Dani Eder mentioned that the incident energy from the sun in the
:	far past might have been far greater than it is now -- and we didn't
:	slide into thermal runaway back then...  perhaps cloud cover changes
:	and resulting albedo changes did provide negative feedback and stem
:	any possible thermal runaway.

The energy from the sun was less in the past.  More on this below.

:	in the case of solar power satellites -- such negative feedback
:	might indeed occur, and reduce the 'naturally' received solar flux.
:	but any negative feedback due to albedo changes would
:	not affect the solar power receiver stations themselves...  they
:	would continue to soak up the same energy and release it as heat...


The Sun's luminosity has been increasing for the last 4 billion years.
It has increased about 30% in this time.  In addition to the slow increase,
there are other, shorter period variations.  There is a small variation
associated with sunspots and random variation on a short timescale.  Changes
in the solar constant over longer periods, hundreds or thousands of years,
are suspected but not confirmed (I am uncertain on the exact state of these
theories; records of solar flux gdo not go back as far as temperature records;
if the "little ice age" was a decrease in solar luminosity then there are 
changes of a few percent over a few hundred years).  More important are the 
long period changes in the earth's orbit (periods of 10,000-30,000 years), 
one effect of which is the ice ages.

The fact that the sun was much less luminous in the past has led to a theory
(see Feb 88 Scientific American) that planets have a negative feedback 
controlling carbon dioxide level which tends to stabilize temperature where 
water is liquid.  The time scale of the feedback mechanism is millions of 
years.  Forests control CO2 on a shorter timescale, but are not sufficient
to control even the present human output.  For a temperature change to cause
a runaway greenhouse effect would require a very long time; long enough to
boil the oceans and release CO2 trapped in rock.  No such delay is needed for
CO2, which has already raised the temperature of the earth by 1-2 degrees
(see Tuesday, Mar 29 (?) New York TImes).


The issue is not whether SPS will be a problem.  If we consume 1% of the 
solar flux worth of power on earth we will generate at least that much 
heat by any method (since the thermally harmless methods can not provide 
that much).  The decisions which will eventually have to be made, if we
continue our expansion, are: do we want heavy industries on Earth?  if
so, can we live with a few degrees increase in temperature?  if we can't,
how do we cool the earth? (a society which consumes so much energy should 
not have too much trouble building machines large enough to cool the earth)



   John Carr           "No one wants to make a terrible choice
   jfc@athena.mit.edu   On the price of being free"           -- Neil Peart