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Global warming due to asphalt? - Page 3

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Posted by daestrom on July 19, 2008, 11:22 pm
 
Bob F wrote:

Well now you've opened a 'can of worms'.  The grass is cooler because a tiny
bit of energy is stored in plant material and most is used to evaporate
water.  But how the energy of that water gets released is complex.  Often it
is given back to the upper atmosphere when forming clouds and rain.  And
that air, being cooler than the air near the planet surface gives its heat
back to space.  But water in the atmosphere is a 'greenhouse gas' in that it
absorbs infra-red radiation from below.  My head hurts thinking about just
some of the factors that are involved.

daestrom


Posted by RicodJour on July 23, 2008, 7:40 pm
 
On Jul 16, 10:54pm, david.willi...@bayman.org (David Williams) wrote:

You make it sound like the mass and color of the object/surface have
nothing to do with absorption of solar energy.

R

Posted by RicodJour on July 24, 2008, 4:51 pm
 On Jul 23, 10:23pm, david.willi...@bayman.org (David Williams) wrote:

Ah.  I apologize for my earlier admonition to quote correctly.  You
apparently can only see your own name.  Don't think of it as a
failing, think of it as "It's all about me."  That works for most
people.


Last I checked the world isn't a perfectly reflective box.  We're also
talking about a system that is open on the local level, not closed,
and there are other factors at work.

How you can say that mass has nothing to do with heat transfer?  A
grassy surface is analogous to fiberglass insulation where the grass
"layer" contains air pockets which effectively slow down heat
transfer.  You can model that anyway  you want, but the net effect is
reduced heat transfer.

You wrote: "The reason why asphalt gets a lot hotter than grass when
the sun shines on it is mainly because water evaporates from the grass
and not from
the asphalt. Very dry grass does get hot, but fresh green grass does
not."

That is simply wrong.  Your did not mention color at all which is
obviously the main factor.  Artificial turf is grass colored and does
not benefit from respiration cooling, yet the surface temperature is
relatively close to real grass.

Strive for consistency.

R

Posted by Steve on July 25, 2008, 2:27 am
 
You are oversimplifying based on ideal steady-state conditions.

A greater thermal mass will take longer to warm up, and thus stay cooler
longer.

The rate of heat transfer is proportional to the difference in temperatures
(IIRC it's one of Newton's laws).

So, as the greater thermal mass increases in temperature gradually, it's
loss to the surrounding air will be less than if it were heated
instantaneously.  Over time the greater thermal mass will lose less heat to
its surroundings as it is absorbing more energy.  It isn't really gaining
more, but has a similar result.

One way to think of the earth is as a spinning sphere.  Energy falls on one
face of the sphere and is radiated from the other.  Certainly the amount of
energy retained by the sphere can be changed by modifying the characterstics
of the surface.  Just like the sphere the earth loses energy to its
surroundings.  It is not a closed system.

Regards,
Steve





Posted by RicodJour on July 26, 2008, 12:25 am
 On Jul 25, 5:38pm, david.willi...@bayman.org (David Williams) wrote:

Several observations, a speculation and a comment.

Observations
- the Earth's rotational speed is slowing.
- tidal and wind effects fit into your "explanation" above, yet void
it.
- your sloppiness in your wording and in your explanations points to
your limited and sloppy understanding.

Speculation
- maybe there are Perpetual Motion Machines at work slowing down the
Earth.  Damn them for not sharing!

Comment
- it's a good thing you are no longer teaching calculus to our youth.
It only takes one bad teacher to turn a kid off math.

R


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