Re: O/T: Up Yours
- From: Fred the Red Shirt <fredfighter@xxxxxxxxxxx>
- Date: Wed, 4 Jun 2008 16:41:42 -0700 (PDT)
On May 17, 5:02 pm, Han <nob...@xxxxxxxxxx> wrote:
...
The scientific principles behind CO2 causing
our planet to heat up are very convincing. Is
CO2 the worst of the gases?
Let's explain those scientific principles-- the
law of conservation of energy, and spectroscopy.
All heat transfer is driven by a temperature
difference. Heat transfers from the sun to
the surface of the Earth because the surface
of the earth is cooler than the sun. Heat transfers
from the Sun to the atmosphere fo the earth
because the atmosphere of the Earth is
cooler than the Sun. Heat transfers from the
surface of the Earth to space because the
temperature of the surface of the Earth is
greater than space. Heat transfers from the
atmosphere of the earth to space because the
temperature of the atmosphere is greater than
that of space. Heat transfers from the atmosphere
of the earth to the surface of the earth, or vice
versa, depending on which is cooler, typically
this transfer is from the Earth's surface to the
atmosphere.
The net rate at which a body radiates energy is
proportionate to the fourth power of its temperature.
The frequency distribution is governed by the Stefan
-Boltzman relationship, the peak frequency of that
distribution rises with temperature.
Conservation of energy requires that for any
system in which heat is exchanged only by radiation,
emissivity will equal absorptivity for any body
that is in thermal equilibrium.
If the emissivity is greater than the absorptivity
the body will lose energy until equilibrium is restored.
If the emissivity is less than the absorptivity the
temperature of the body will rise until equilibrium
is restored.
(For a body in thermal equilibrium the difference
between unity and the absorptivity is therefore
equal to the difference between unity and the
emissivity and is called reflectivity, and the ratio
of reflected energy to incidental energy is called
the albedo.)
A the temperature of the solar photosphere, the peak
of the emitted spectrum is in visible light. The gases
that comprise the Earth's atmosphere are mostly
transparent to visible light so most of that gets
to the surface where it is absorbed, and converted
to heat, a process called themalization. Some is
thermalized in the atmosphere and some is
reflected form both.
At the temperature of the Earth's surface the emission
peaks in the infrared range. Carbon dioxide has strong
infrared absorption bands. Thus it strongly absorbs some
of the infrared emission from the Earth's surface. This
energy is thermalized in the atmosphere, reducing
the temperature gradient between the Earth's surface
and the atmosphere. All gases that behave that way
are called greenhouse gases. They all have the effect
of raising the temperature of the Earth above what it
would be if there were no greenhouse gases in the
atmosphere.
Now, how much do the greenhouse gases raise the
temperature? While the above relationship is clear
from theory, quantifying the effect is a bit tougher.
What would be cool is if we had a control, that is a
planet the same average distance from the Sun,
but without an atmosphere. And, we're in luck,
we do. So we can get a handle on how effective
the greenhouse effect is by comparing the temperature
of the earth's surface with the moon. The temperature
at the surface of both varies on a daily annual and on
a geographical basis. But it averages out to be about
298 k for the Earth and 238 K for the moon. The
Moon is about 50 degrees (K) cooler than the Earth.
The moon also has a lower albedo, if they were the
same that difference should be greater.
Thus, all other things being equal, adding more
greenhouse gas, like Carbon dioxide to the atmosphere
will make the planet wrmer while removing it will
make the planet cooler.
And THOSE are the scientific principles behind
CO2 causing our planet to heat up There are,
and have always been, other scientific principles
causing our planet to heat up and cool off which
is why no one can prove or disprove a causal
relationship between any of them and the temperature
of the Earth using climate data alone.
Note, we did NOT compare the Earth to the Moon
to determine if there was a causal relationship
between atmosphere and surface temperature.
That determination was made using physical
theory. Determination of causality requires
a theory.
The comparison was done to get a handle on
the MAGNITUDE of the effect tha tis predicted
from the underlying theories--the law of conservation
of energy and spectroscopy.
--
FF
.
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