epiphiny43 -> RE: An Attempt to Understand the Science Behind Global Warming (9/29/2013 5:57:54 PM)
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The 'crystal' and dopant' analogies are specious. Several corrections to Hillwilliams overview: The atmosphere is NOT generally transparent to all electromagnetic radiation. It IS transparent to a high degree to 'visible' light. Just like 'sand glass', used for greenhouses. Same principles, same result. Water content among others like methane and CO2 greatly lowers IR transparency. The 'window' of visible light combined with evolution, resulted in most surface animals have evolved eyes to utilize all significant surface 'light'. Birds and many insects see further into the UV range than mammals, it seems related to food choices where plant differences (flowers, etc.) in UV reflectivity are useful, not for omnivore or carnivore mammals. The CO2 doesn't so much reflect as absorb IR radiation. It re-radiates it's molecular heat as IR again in all directions, acting as a low quality mirror to any significant IR energy flow, a thin layer (OP's conceptual crystal) would have little effect with multiple 'not-long' re-radiant paths. When the atmosphere's useful density is in miles, it matters. The result is higher temps at the bottom (If I have to explain the Adiabatic Lapse Rate, you DON'T yet belong in this discussion!) where heat is more effectively trapped. No matter the amount of heat trapped or the mechanism, Hillwilliam's note on Balance arising over time holds. Change the composition of the atmosphere (or the radiant energy of the Sun) and the surface temps of Earth will move to a new 'balance', or equilibrium. There is a Lot of energy coming in daily and a Lot leaving. We are closing a small door for energy exit. Enough to matter! Do a massive CO2, particulates and sulfur dioxide injection into the atmosphere (Deccan Traps, Pinatubo, Mankind's discovery and use of coal and oil on industrial scales) and you get a short or longer term change in radiant energy reaching the lower atmosphere and surface, and leaving for Space. (Depends on the injection volume and species of gasses, particle size and the height of the injection.) Which results in a new balance or a dynamic situation as the changing compositions and properties affect visible and IR radiation into and out of the different parts of the atmosphere. It seems incontrovertible that human 'civilization' has about doubled the CO2 concentration in the important (Thickest, lowest) parts of the atmosphere in recent historical time. No large scale volcanism or extra-planetary impacts seem of sufficient scale and the numbers for the carbon in forests cleared and the fossil fuels 'liberated' for energy closely match the observed tonnage of CO2 in our air. Long term questions of how fast unusual levels of greenhouse gasses persist, what mechanisms sequester them, how Long they sequester for each mechanism and what feed back mechanisms with increasing planetary surface temps liberate new CO2 (Some in catastrophic state changes, far above logarithmic!) remain to be given satisfyingly precise numeration. This in no way means global warming isn't happening. Like a car skidding off the crown of an icy highway, not knowing the final result doesn't mean an accident isn't in progress.
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