On Fri, 31 Oct 2008 14:20:37 -0400, AR- wrote:



Bill Ward wrote:

On Fri, 31 Oct 2008 08:36:36 -0700, Bolaleman wrote:


On Oct 31, 6:07 am, chemist wrote:

On Oct 31, 1:45 am, Roger Coppock wrote:






The TV science series "Mythbusters" did a "Young Scientists Special."
It aired on 4/26/08 (Season 6, Episode 8). One of the items they
put to the test was greenhouse gas theory. They made 4 large
rectangular chambers added CO2 to one, CH4 to another, and used the
remaining two for controls.

They simulated the Earth by shining a light through the clear mylar on
one side onto a black painted surface at the other side. the
greenhouse gas chambers were warmer and melted more ice than the
control groups. They confirmed that CO2 and CH4 can cause greenhouse
warming.

Tom Bolger should look at this demonstration to see how to do this
correctly. He's failed too many times and he needs help.

I found my copy on the LImewire™ network. This episode is probably
also available on DVD. Please see:

http://www.imdb.com/title/tt1225053/

Give us more detail such as
were the containers open.
METHANE DOES NOT WARM FASTER THAN AIR.- Hide quoted text -

- Show quoted text -

Chemist, here is the reason:
When heat is lost to the air, some is absorbed by nitrogen, some is
absorbed by oxygen, and a tiny amount is absorbed by argon, carbon
dioxide, water vapor, and trace gases. You can write:

Heat absorbed by one mole of air = heat absorbed by O2 + heat absorbed
by N2 + ...
= xO2Cp(O2) T + xN2Cp(N2) T + ...

where xO2 and xN2 are moles of oxygen and moles of nitrogen per mole of
air, and Cp(O2) and Cp(N2) are the constant pressure molar heat
capacites for pure oxygen and nitrogen gases.

Assuming that air is 21% oxygen, and 79% nitrogen by volume. If you can
assume that the air behaves ideally, Avogadro's law says that the volume
fraction for each gas is also its mole fraction. However, gases like
CO2, H2O and methane (CH4) do not behave like an ideal gas.

As O2 and N2 are di-atomic gases, but CO2, H2O and methane are three-
and four- atomic gases, they have more degrees of freedom, i.e. infrared
energy can be converted more easily into intra-molecular atomic
vibrations which is equal kinetic energy or heat energy. As a result,
these gases (including water as vapor) are heated up more easily than
oxygen and nitrogen by Infrared (IR) radiation. This conversion of
radiation energy to kinetic energy by the way is the principal of IR
spectroscopy. The higher energetic ultraviolet radiation (UV) is causing
excitations of outer electrons (used for instance in the UV
spectroscopy). This “absorbed” energy can be converted partially in
kinetic swinging energy (resulting in heat production) and partially is
emitted again as radiation energy.


Fine, but IR has nothing to do with it. The experiment heated the gases
by conduction and convection from the black background.

Unfortunately there is no link to the video so I have only a sketchy idea
of how this experiment was conducted. But if there was a black background
behind the chambers it would generate IR radiation. The original light
source that passed through the chambers would also (unless it was of a
type or specifically designed not to). Thus, IR should have been involved
in this experiment. Though what you maybe saying, is that the main heating
effect (i.e.,much greater than the contribution from IR) given this
experimental set up, was conduction and convection.

That is correct. Conduction and convection (mass transport) are far more
effective than radiation at ambient temperatures. That's why most
computers have fans, for example.

Even back in the
1850's, Tyndall pointed out the need to keep the radiation source and
detectors completely thermally isolated from the sample gas. It's
still true.

Those demonstrations do not show anything but the density and thermal
properties of the gases. They are being shown to gullible children as
propaganda.

You may be right, but that seems rather unnecessary. It surely cannot be
that difficult to set up a simple laboratory experiment, even one that's
portable, which shows the differential ability of some gasses to absorb
radiation.

It is difficult (and expensive), because of the need to thermally isolate
the sample gas with IR transparent optics, and the expensive, cooled IR
sensors necessary to detect IR in the 15u band in question.

There's not much serious dispute about the absorption spectrum of CO2,
it's the relevance to global warming, in view of the larger effect of
water and its phase changes, at issue. The only effect CO2 could have is
above the troposphere, and negative feedbacks from water make even that
unlikely.

Don't believe anything until you are satisfied you clearly understand it.
The burden of explaining a theory in a clear, accurate and understandable
manner lies with the proponents, not the skeptics. Be very suspicious of
those who try to convince you that you are so stupid you can't understand
their explanation. That's just their way of discouraging you from asking
questions they can't answer without exposing their ignorance.