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Re: Earth thermodynamics




On Wed, 11 Jun 1997 08:45:16 -0500 JON GREENBERG <JON@AIT.NET> writes:
Tom Wayburn's idea is interesting, though I am not
the person who can help him with these questions.

Tom, do remember some other energy sources for the
Earth-atmosphere-biosphere system:

Heat generated within the Earth by rqadioactive decay
and friction under moving crustal plates produces
volcanoes, earthquakes, and hydrothermal vents that
probably support most of the world's biomass without
(much) benefit from photosynthesis. There is (I think)
still a little heat left over from the gravitational
compression of the Earth.

Then there is the energy (re-)introduced to the system
by electricity generation, fossil fuel burning, etc....

Jon Greenberg
Science Editor/Curriculum Developer
Agency For Instructional Technology
jon@ait.net

***********************************************
Hi Jon, Thanks for replying. I would be shocked to discover that
volcanism plays a big role; but, in any case, I excluded the core of the
earth from my control volume, as we ought not tamper with it, I think.
Also, the other availability sources you mentioned would violate the
steady-state condition I imposed in the problem statement. Burning
fossil fuels, for example, represents a diminution in the Helmholtz
availability, U - T(surr)S, within the control volume, which was a
sphere concentric with the earth but 100 miles greater in radius so as
to include the atmosphere but excluding the core of the earth (for that
matter, most of whatever is moderately deep underground).

Since I will broadcast this reply, I think it might be worthwhile to add
a few words concerning the relevance of the exercise: The number in
terawatts will be very large and will dwarf our (human) availability
budget. Most of the availability is consumed by irreversibilities in
our weather and other business done by Mother Nature, which, of course,
is essential to our survival. At least I think so. Nevertheless, we
will get an impression of the relative magnitudes of Nature's business
and human business. This huge disparity is not calculated to favor the
soft-energy position held by myself and others. Still it is instructive
regardless of its usefulness as propaganda :-) .

One might compare the work that could have been done by Nature ( but was
not done because Nature is not reversible) to the amount of availability
captured by photosynthesis. The disparity is great, but not so great.
Finally, one sees that, however large the hard upper bound on
availability at our disposal may be theoretically (which, of course, is
lost in the real world), the quantity is finite; and, if it be exceeded,
the earth is deficit spending, which amounts to an availability debt that
must be repaid or defaulted upon - eventually at our peril. Also, when
we compare the availability consumption that most Americans feel they
can't do without to the availability captured by photosynthesis (and by
whatever other processes are active), a moment's reflection shows that
we have no hope of harvesting in a sustainable way so much as we have
been spending in a non-sustainable way.

The upshot, regrettably, is that, whereas we have no proven sustainable
alternative energy technology, i.e., a technology that has a
non-negative availability efficiency when indirect availability costs
are counted, we are not doing the research to find out just how
desperate our situation is as the petroleum era draws to a close (not
tomorrow or even very very soon, but inevitably); and, with very few
exceptions, we are not developing reasonable candidates for a *feasible*
sustainable primary energy technology that can replace petroleum even at
a survival level - supposing that rational people have long since
abandoned dreams of a Buck Rogers future with space travel and marvelous
abundance for everyone.

Now, unless by "development" we mean (drastic) economic shrinkage,
"sustainable development" is a chimera. This sort of talk (by me at
least) has made virtually no impression upon scientists with whom I have
spoken with, written to, and addressed at "scientific" meetings.
Clearly, effectiveness is a function of who is doing the talking rather
than what is said; and I am practically a nobody (outside of a pitifully
small circle of colleagues who do not want to hear this message as their
livelihoods depend upon them being ignorant of it).

So, I look to this little group of physicists, many of whom have not won
even a single Nobel Prize. In you (and your good sense) lie my present
hopes.

Best regards to all / Tom
713-963-8944

P.S. Help!!!!