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Saturday, April 29, 2006

The Real Inconvenient Truth: Greenhouse, global warming and some facts

 I'm sorry, and correct me if I'm wrong, but I have to take exception to the post over at junkscience.com concerning global warming. I only read as far as the part shown below to find fault. I really don't like the obtuseness they display in their argument about how a greenhouse works. According to the authors a greenhouse is merely a barrier to convection, but I say that it is more and that if they are correct then you could build a grenhouse out of brick or stainless steel. I say that uni-directional transparency to solar radiation is a MAJOR component of the greenhouse's attributes. So, no, the gases don't act as physical barriers to convection like glass does in a greenhouse but the gasses to act as uni-directional barriers to radiation. Sheesh! And I only have a H.S. diploma. --pseudolus
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- Basic misconceptions that must be addressed include:
 
Does the Earth's atmosphere primarily behave like an actual greenhouse?
 
No. The term "greenhouse effect" is unfortunate since it often results in a totally false impression of the activity of so-called "greenhouse gases." An actual greenhouse works as a physical barrier to convection (the transfer of heat by currents in a fluid) while the atmosphere facilitates convection. So-called "greenhouse gases" in the Earth's atmosphere do not act as a barrier to convection so the impression of actual greenhouse-like activity in the Earth's atmosphere is wrong.
 
Supplemental, April 25: A couple of people have written challenging whether physical greenhouses function as convection barriers since they do radiate and so does the atmosphere - apparently we need to expand on this point. To begin with, a physical greenhouse is simply a contained subset of the atmosphere - it is not bounded by the near-vacuum of space as is the planet's atmosphere and so has rather different properties. The proof that convection containment is critical to the function of physical greenhouses is that it is possible to create structures with similar radiative properties, one which allows convective activity between the structure and unconstrained atmosphere and one which does not. Only the structure constraining internal-external convection will function as an effective greenhouse. Greenhouse gases categorically do not inhibit convective activity and so are not like a physical greenhouse.
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1 Comments:

Anonymous Anonymous said...

Yeah, you're right and the non-scientist at junkscience is wrong. Glass works just like a greenhouse gas, letting optical light pass through AND HOLDING BACK INFRARED LIGHT -- exactly what greenhouse gasses do in the atmosphere. You can open up a greenhouse to allow convection, and it will still be warmer in the greenhouse than outside. The key part to making a working greenhouse is NOT blocking convection, but letting in optical light and keeping in infrared light. Sure, it's more effective to prevent heat loss through convection, but that's not the primary reason why a greenhouse works.

In any even, junkscience.com is the front for a corporate shill.

8/16/2006 1:08 PM  

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