|The Ghost of Paley
Joined: Oct. 2005
From B.V.'s source:
| Our manmade materials have not have a true effect on the atmosphere. We would have to try really hard if we wanted to make a dent. So much more of this chlorine (which is the bad part in CFCs) occurs naturally than we make. A large volcanic blast can contribute 100 to 1000 million tons of active chlorine to the atmosphere, and a large portion of it may very well reach the stratosphere. Slower eruptions make a slow stream of chlorine, like Mount Erebus which has released 300,000 tons per year for the past 30 years Salt spray from oceans, forest and brush fires contribute an average of 700 million tons annually! All of these natural contributions add up to make a total four to five orders of magnitude greater than the man-made contribution. Also, take into fact that only a very minor portion of CFCs actually make into the stratosphere. The molecules are 4 to 8 times heavier than air and adhere easily to the ground and other things attached to the ground. |
No doubt about it, whoever wrote this is ignorant. From the source I cited earlier:
|Myths about ozone depletion|
Various untruths and halftruths about ozone depletion are prevalent. A few of the most common are addressed briefly here; more detailed discussions can be found in the ozone FAQ.
CFCs are "too heavy" to reach the stratosphere
One frequently hears that since CFC molecules are much heavier than nitrogen or oxygen, they cannot reach the stratosphere in significant quantities.  But atmospheric gases are not sorted by weight; the forces of wind (turbulence) are strong enough to fully intermix gases in the atmosphere. CFCs are heavier than air, but just like argon, krypton and other heavy gases with a long lifetime they are uniformly distributed throughout the turbosphere and reach the upper atmosphere. See  and the FAQ, part I, section 1.3.
Manmade chlorine is insignificant compared to natural sources
One occasionally encounters statements such as It is generally agreed that natural sources of tropospheric chlorine (volcanoes, ocean spray, etc.) are four to five orders of magnitude larger than man-made sources. This falls into the "true but irrelevant" category as tropospheric chlorine is irrelevant; it is stratospheric chlorine that matters. The chlorine from ocean spray is in the form HCl and is soluble; it never reaches the stratosphere. CFCs, in contrast, are insoluble and long-lived and hence do reach the stratosphere. Even in the lower atmosphere there is more chlorine present in the form of CFCs and related haloalkanes than there is in HCl from salt spray, and in the stratosphere the organic source gases dominate overwhelmingly. This includes the CFCs and methyl chloride, which has both natural and man made sources (FAQ, Part II, section 4.3). Another point which must be kept in mind when evaluating the contributions of various gases to stratospheric ozone is that methyl chloride molecules only contribute a single chlorine atom, but CFC molecules contribute multiple chlorine atoms. Very large volcanic eruptions can inject HCl directly into the stratosphere, but direct measurements (FAQ, Part II, section 4.4) have shown that their contribution is small compared to chlorine from CFCs.
|On a final note, remember that the first major hole in the ozone above the Antarctic (that we noticed) was in 1956, long before chlorofluorocarbons were in widespread use. This "hole" is a naturally occurring event that happens periodically. |
|An ozone hole was first observed in 1956|
G.M.B. Dobson (Exploring the Atmosphere, 2nd Edition, Oxford, 1968) mentioned that when springtime ozone levels over Halley Bay were first measured, he was surprised to find that they were ~320 DU, about 150 DU below spring levels, ~450 DU, in the Arctic. These, however, were the pre-ozone hole normal climatological values. What Dobson describes is essentially the baseline from which the ozone hole is measured: actual ozone hole values are in the 150-100 DU range.
The discrepancy between the Arctic and Antarctic noted by Dobson was primarily a matter of timing: during the Antarctic spring ozone levels rose smoothly, peaking in April, whereas in the Antarctic they stayed approximately constant during early spring, rising abruptly in November when the polar vortex broke down.
The behavior seen in the Antarctic ozone hole is completely different. Instead of staying constant, early springtime ozone levels suddenly drop from their already low winter values, by as much as 50%, and normal values are not reached again until December. (FAQ, Part III, section 6)
As for the "UVB is harmless" claim.....
|The big problem the environmentalists and the public had was the "infamous, deadly UV rays". Well there are different kinds of UV rays. The shorter wavelength type, UVC, is responsible for splitting oxygen molecules, and creating billions of tons of ozone per second. The longer wavelength type, UVB, breaks it down. Both UVC and UVB are effectively blocked by the ozone layer. The longest wavelength, UVA, is not affected by oxygen or the ozone layer and passes through freely. Ironically, this is the wavelength proven to be the cause of melanoma, the deadly skin cancer. |
Nice try, Lex Luthor!
|UVB (the higher energy UV radiation absorbed by ozone) is generally accepted to be a contributory factor to skin cancer. The most common forms of skin cancer in humans, basal and squamous cell carcinomas, have been strongly linked to UVB exposure. The mechanism by which UVB induces these cancers is well understood — absorption of UVB radiation causes the pyrimidine bases in the DNA molecule to form dimers, resulting in transcription errors when the DNA replicates. These cancers are relatively mild and rarely fatal, although the treatment of squamous cell carcinoma sometimes requires extensive reconstructive surgery. By combining epidemiological data with results of animal studies, scientists have estimated that a one percent decrease in stratospheric ozone would increase the incidence of these cancers by 2% .|
Great link, guy.
Also see this page:
UVA, UVB and UVC can all damage collagen fibers and thereby accelerate aging of the skin. In general, UVA is the least harmful, but can contribute to the aging of skin, DNA damage and possibly skin cancer. It penetrates deeply and does not cause sunburn. Because it does not cause reddening of the skin (erythema) it cannot be measured in the SPF testing. There is no good clinical measurement of the blocking of UVA radiation, but it is important that sunscreen block both UVA and UVB.
UVA light is also known as "dark-light" and, because of its longer wavelength, can penetrate most windows. It also penetrates deeper into the skin than UVB light and is thought to be a prime cause of wrinkles.
UVB light can cause skin cancer. The radiation excites DNA molecules in skin cells, causing covalent bonds to form between adjacent thymine bases, producing thymidine dimers. Thymidine dimers do not base pair normally, which can cause distortion of the DNA helix, stalled replication, gaps, and misincorporation. These can lead to mutations, which can result in cancerous growths. The mutagenicity of UV radiation can be easily observed in bacteria cultures.
This cancer connection is one reason for concern about ozone depletion and the ozone hole.
As a defense against UV radiation, the body tans when exposed to moderate (depending on skin type) levels of radiation by releasing the brown pigment melanin. This helps to block UV penetration and prevent damage to the vulnerable skin tissues deeper down. Suntan lotion that partly blocks UV is widely available (often referred to as "sun block" or "sunscreen"). Most of these products contain an "SPF rating" that describes the amount of protection given. This protection applies only to UVB light.
If you don't trust Wikipedia, try here:
|There is convincing evidence that UVR can cause damage to DNA and in animal experiments it has been shown to be a cause of cancer. The International Agency for Research in Cancer (IARC) has concluded that solar radiation, broad spectrum UVR, and UVA, UVB or UVC radiation are all carcinogenic to experimental animals (IARC, 1992). Exposure to UVR also increases the risk of skin cancer in man and produces other undesirable health effects. The main tissues of the human body affected are those of the skin and the eye. There are also effects on the immune system, the significance of which for human health is not yet clear. The principal known beneficial effect of UVR exposure is its role in the production of vitamin D in the skin. |
The most serious adverse health effects for which exposure to UVR is a recognised risk factor are the cutaneous malignancies (skin cancers). UVB has been recognised for some time as carcinogenic in experimental animals, and there is increasing evidence that UVA, which penetrates more deeply into the skin, also contributes to the induction of cancer. UVC from the sun is absorbed by the Earth's atmosphere, and any arising from artificial sources does not readily penetrate to the sensitive basal layer of the skin.
Pathological responses of the human eye to excessive UVR exposure include photokeratitis and photoconjunctivitis (inflammation of the cornea and the conjunctiva, respectively). Repeated exposure is considered to be a major factor in the causation of non-malignant clinical lesions of the cornea and conjunctiva such as climatic droplet degeneration (discrete areas of yellow protein deposits in the cornea and conjunctiva), pterygium (an overgrowth of the conjunctiva on to the cornea) and, probably, pinguecula (small yellow growths in the conjunctiva). Damage can result from exposure to UVA, UVB and UVC.
There is epidemiological evidence that chronic exposure of the eye to intense levels of UVR contributes to the development of cortical cataract. Evidence for a causal role of solar radiation in macular degeneration (a major cause of blindness) is conflicting. The extent to which UVR exposure is an important risk factor for cataracts in the general population is unclear, as is its relation to eye melanoma.
There is good evidence that prolonged gazing at very bright light sources, particularly those emitting shorter wavelength blue light, causes retinal damage resulting in transient or permanent loss of visual acuity. Staring at the sun can damage the retina permanently. Such an effect would normally be prevented by the natural aversion response invoked by looking at a bright light, but this response can be intentionally suppressed. Similar damage has also been induced in the non-human primate retina following acute exposure, particularly to blue light. It is not clear to what extent UVA is involved as its transmission through the lens is low in adults but is higher in children.
Dey can't 'andle my riddim.