Re: global warming ! (NDC)


"Leigh Orf" <orf@xxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:eub6gs$kb6$2@xxxxxxxxxxxxxxxxxxx
S McFarlane <nospam@xxxxxxxxxxxx> wrote:


I was thinking more in terms of it's affect non-locally. That it would
affect the amount of energy retained by the system as a whole. So, a
different mechanism but same result as increased greenhouse gases.
Perhaps
that's just a psychological thing afflicting people in areas experiencing
rapid growth. It sure seems like all that concrete has got to be a
seriously bad thing...

Careful with phrases like "energy retained by the system." You have to
define the system first!

Above I had the earth and it's atmosphere as 'the system'. My rudimentary
understanding of the GE is that radiant energy hitting the earth's surface
is partitioned. Part of it is absorbed by the surface, while some of it is
reflected back, mostly in the IR region. So the reflected radiation has a
directional component away from the center of the earth. Some of that
radiation excites absorbers in the atmosphere, and the resulting emissions
have no net directional component. So, some energy that was directed
towards the system boundary is absorbed and emitted back to the surface,
effectively lowering the energy flux out of the system and thereby creating
a higher equilibrium temperature than would have been the case without
absorbers. So far not too far off-track?


The UHI effect does a couple of things (this is all available elsewhere
but what the heck). It changes the albedo, it changes the heat capacity,
and probalby most importantly, it changes the runoff characteristics
of an area. A lot of the energy of the sun goes into evaporating water
(including transpiration in vegetation). When you take all the water
away (via runoff into storm sewers etc) that solar energy instead goes
into things like heating asphalt. Which causes the surface to be much
warmer than it would have been otherwise.

The heat capacity of concerete etc. allows for warmer nights, as the
heat of the day is "stored" in the thick concrete etc. The Pueblo
Indians built their structures to take advantage of this effect, such
that the heating cycle was out of phase with the diurnal cycle by about
12 hours (inside of structure warm at night, cool during the day).

Of course, air conditioners play a role here. You can't cool without
heating! The backside of the AC unit gets quite hot, and this effect is
probably non-negligible over a large area.

My guess is that the effect of AC units is mostly to be found in gas
emissions at the generating plant. Now that definitely would impact
temperatures.


The reason why the UHI effect is not a major contributor to global
warming is that, averaged over the area of the earth, urban areas are
still a small fraction of the total area. Climatologists have long known
that the UHI signal needs to be removed from nearby observation stations
because it does NOT represent a very large area.

Ahh. That's sort of what I was getting at. You are suggesting that a
change in surface reflective characteristics _would_ change the energy flux
into the system (and therefore push the equilibrium temperature one way or
the other). We just haven't changed surface characteristics enough to make
an appreciable difference. Do I have that right? So there is theoretically
a mechanism for urban sprawl to impact global temperatures, but we are still
a long way from reaching that point?



As far as local conditions are concerned - and this is strictly
anectedotal - I'd swear that in the summer temperatures are
higher in the center of the metroplex relative to the outlying
areas. I'm almost sure I've seen that pattern. Maybe just a
trick of the mind...

Absolutely true! But that is local. If it were not local, the outlying
areas would be just has hot, right? That's why it's called an "Island."


That last bit was a reaction to what Ray was saying about the UHI effect
still being in play (that is, the question of whether it really exists).
Rereading his last remark now, I see that he was also not claiming that
there is no mechanism for UHI effect to influence global temperatures, but
rather that if the mechanism exists, it's effects are neglible. Sounds
reasonable to me.

Scott


.

Relevant Pages

  • Re: ILE - The Ideal Lane-Emden Equation
    ... The point is that if Saturn is a "hydrogen planet" it's easy to explain ... average kinetic energy is 1/2 of the average potential energy. ... This is true for a 1/r potential which implies esentially an ideal gas. ... These factors start to affect your temperatures significantly even ...
    (sci.astro)
  • Re: Universal grammar
    ... switch off their metabolism at those temperatures. ... As for superconducting, one does not know the maximum temperature. ... The life is using the form of energy it has found available at the planet. ... definition of language again: ...
    (sci.lang)
  • Re: ROGER COPPOCK explain how this confirms AGW
    ... a 12 month running average of monthly satellite SH temperatures, ... Plotting the the annual change in CO2 in as a 12 month running ... I get a correlation of 0.552 if the CO2 is lagged. ... doesn't gravity/tidal energy account for anything within your ...
    (sci.energy)
  • Re: ILE - The Ideal Lane-Emden Equation
    ... average kinetic energy is 1/2 of the average potential energy. ... at these temperatures it isn't really ... the denser planets as well in my ideal gas model. ... the physics of the corresponding materials for these conditions. ...
    (sci.astro)
  • Re: dipole antenna for sunlight
    ... my pysics texts, optics texts, optical electronics texts, and just ... As a physicist I tend to believe that the only way a photon can be ... totally captured is when it contains a discrete quantity of energy ... Blackbody solar absorbers seem to work reasonably well if the heat is ...
    (sci.energy.hydrogen)
Loading