At 10:06 PM 12/23/2004, Jeff Condit wrote:
I don't know all the ways various slowdown amounts would affect various
things, but clearly at some point it would affect the weather and climate.
Yes, of course. The real question, though, is whether or not any reasonably
likely implementation of tidal energy generation would make a noticeable
acceleration in the slowdown. My sense is not. The earth's rotation is
already slowing by, I found, 1.5 milliseconds per century, due, I presume,
to tidal forces from the earth and moon.
One estimate I saw shows that throughout history natural tidal friction
loses about 1023 J per century.
Which corresponds, then, to a slowing of the day by 1.5 milliseconds
However, most of the tidal surges are in
places which are broad, and the water is free to flow in and out over the
entire period with relatively low flow rates and very little elevation
change across the system. Damming up the natural system prevents this flow
until the peak tide where there is an elevational difference if many meters
across the dam.
Damming the system globally could, I suppose, increase effective tidal
friction substantially. However, such massive tidal projects are not, to my
knowledge, being contemplated.
As of 1999 the DOE estimate of global energy use was 4.02x1020 J but
increasing rapidly with emerging 3rd world infrastructures. I don't have a
more recent number, but worldwide efferts to curb this energy rise may have
had some effect. Thus at the current usage we may be slowing down a second
per year every decade or so.
Doesn't this assume that all the energy is coming from an increase in tidal
friction? Which is not even close to true?
You can do your own studies if you like. What
I don't like is that this is never talked about.
*This* particular problem is a long way from raising its head.... Nearly
all energy generation does not increase tidal friction at all. Only if
truly massive structures were created could a significant effect be created
on tidal friction. Further, some of the energy that would be generated
would simply be a substitute for energy expended in raising the earth's
temperature due to tidal friction. Instead of the heat from the movement of
the tides being dissipated in the shoreline and ocean, some of it would be
converted into power and dissipated remotely. I don't find it obvious how
much a power generation system would necessarily increase tidal friction,
even if massive. In other words, all that tidal movement already interacts
with the shore and the ocean itself to generate heat; the energy of this
heat is subtracted from the rotational energy, thus slowing the earth (and,
as it happens, speeding up the moon). A tidal generation system would not
necessarily generate more heat, it would depend, I would guess
off-the-cuff, on the exact design.
But even if the increase would be substantial, the project would have to be
by far the largest thing ever constructed by humans in order to have a
significant impact.
I'm all for anticipating environmental consequences, but I think this one
is not realistic unless a *huge* effort were put into constructing massive
systems, and presumably, before anything like that were done, there *would*
be consideration of the consequences. It would take a long time to build
the system, plenty of time for people to notice the problem and object.
I think the effects from heating the earth due to solar collection are more
likely to be significant, but even there, the effects would still be much
smaller than what we get from altering the atmosphere by emitting CO2.
The studies I have read on planetary atmosphere kinematics indicate wind
patterns are a product of both tidal effects on the atmosphere and daily
heating cooling cycles. As a result, harnessing wind would probably have a
lesser effect on the rotational kinetic energy.
Again, much less, because wind systems are not going to cover the massive
areas that are involved in tidal friction.
In large desserts the ground normally reflects a certain aomunt of radiant
energy back into space while absorbing some as heat. If large solar atrrays
in the dessert could the same anount as the normal soil, then to overall
heating of the Earth would be unchanged.
But this is unlikely. Large solar arrays would, I believe, necessarily have
a lower albedo, substantially, than your default desert surface. However, I
*still* think that the effect will be small compared to the atmospheric
ones that we are already "enjoying."
The difference would be that
energy would be transferred from the dessert to other clode-by wetter areas
where people live, thus the dessert would be a bit cooler while the
surrounding areas would be a bit warmer.
I don't think the desert areas would be cooler. They would be warmer,
unless somehow it is managed to get very high efficiency in energy
conversion. And so would the areas to which the energy collected is
transferred.
Note that my own preferred futurist scenario for energy generation would be
satellite solar power. In this case, the energy is collected in space,
albedo is not a consideration. The collection antennae would be effectively
transparent to radiant heat; so, while there would be some local heating in
the area of an antenna, it is quite possible that the use of the land
underneath the antenna would be such as to increase albedo, thus lowering
solar heat retained. So the net effect in the area of the collection
antennae would depend on the land usage underneath the antenna. (The
L5/Oneill/SSPS people suggested using it for agriculture, which might lower
albedo, but it does that anyway....). The efficiency of the energy
transmission system from space to earth was projected at about 90%. I don't
know what portion of that ends up as heat at the receiving antenna. But
there is, unavoidably, heat generated at the point of energy use. Again,
however, if this were large enough to be of concern, it might be possible
to balance it by arranging for increased reflection of solar energy
reaching the earth, back into space. For zero net effect.
This could cause weather shifts
and slight local climatic changes, but the global effects would be
minimized. Of course, this approach would never be taken because solar
power is expensive, and so is driven by economics which mandate maximum
power conversion per $ invested, resulting in dark colored panes that do not
reflect much of their incident radiation on purpose.
Yes. If the solar collection panels are at earth surface, I think this is
unavoidable. However, if they are in space, it is not a relevant concern.
The waste heat would be reradiated from the panels into space.
It has been stated that the Earth regulates its own temperature via
increasing cloud cover as global temperatures rise. This is a negative
feedback system. However, geologic evidence indicates the duration of ice
ages is long, which in turn suggests the Earth has at least two stable
states, not just one. (Stable in the shorter term; since the ice ages come
and go in the long term.) Thus if the Earth gets covered with clouds and
subsequently cools down, it does not necessarily lose its cloud cover for a
very very long time even though it gets cold. I think we need to be
focussing on harnessing the renewable energy flowing around the planet and
redirecting it in constructive ways that do not alter the global energy
budget. We should not be beaming in copious amounts more from satellites,
or messing with planetary kinematics, regardless of who's $ is talking. And
we should not be boosting the conversion of convenient stored energy well
beyond sustainable levels except (perhaps) to promulgate an exit from an ice
age.
Satellite solar power should have no effect on planetary kinematics. It
should also, properly implemented, not change the earth's heat budget. Yes,
like all energy usage, it will add heat to the environment, but it is not
this heat which is really the problem today, and that contribution could be
balanced rather easily. The serious problem is the change in the atmosphere
from fossil fuel burning, which then causes changes in heat retention by
the earth, thus leading quite likely to global change. Satellite solar
power could contribute, in the construction phase, to atmospheric change,
from massive booster exhaust gases; however, the bulk of the construction
in the L-5 conception was to take place from lunar materials. The
engineering was worked out over twenty years ago; the obstacle was not
practical, nor was it economics, really, but politics.
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