The "ozone hole" is much in the news, and many think it impacts just the
Arctic and Antarctic regions. Not so: there has been a nearly global
decrease in earth's ozone shield. One possible effect of this was addressed
in the article _Amphibians in a Bad Light_, by Andrew Blaustein, in the
10/94 issue of Natural History (American Museum of N.H.), where evidence
is given that increasing UV-B (middle portion of ultraviolet light band)
is causing the failure of amphibian embryo development. This cannot be
the whole story, but the loss of stratospheric ozone is a serious matter.
Here is a "sidebar" from the article:

  "The ozone layer is thinning, but how much is being lost over any
  particular part of the globe varies according to lattitude and
  season. The computer generated image below [not attached - fw] shows
  that significant losses have occurred over populous regions of Asia,
  Europe, and North America (demonstrating that the ozone hole over
  Antarctica is not our only problem). The image shows the change 
  between the level of ozone in March 1993 - a particularly bad year -
  and the average March level between 1979 and 1990. At midlaltitudes,
  ozone levels (blue areas) are between 10 and 15 percent below the
  previous average, and nearer the pole they are as much as 20% below
  normal (purple). The red band over the Tropics shows a slight increase.
  The small black circle at the North Pole represents polar night, where
  no measurements were made.

  "Ozone is vital because it is the only component of the atmosphere that
  absorbs damaging ultraviolet radiation (UV-B) from the sun. The depletion
  of this protective layer, even by small amounts, may therefore have dire
  consequences for many organisms, including ourselves. Ozone, a blue-tinged
  gas that is a form of oxygen with three atoms instead of the usual two,
  is easily broken down by the chlorofuorocarbons and other pollutants
  that humans have dumped into the atmosphere. Despite international 
  efforts to phase out the manufacture of the most destructive chemicals
  by the end of this century, some of those already released will persist 
  in the stratosphere for many decades, eating away the ozone layer
  faster than can be replenished naturally.

  "Quantifying the rise in UV-B radiation that accompanies the loss
  of ozone is complex, due to variable cloud cover and a host of other
  factors, but even a small loss of ozone can have large effects. One
  United Nations report calculated that even a one percent loss of ozone
  results in an extra 50,000 skin cancers and 100,000 cataracts worldwide.
 
  "A recent study of UV-B levels conducted by James B. Kerr and C. Thomas
  McElroy, of Environment Canada in Downsview, Ontario, gives some idea
  of how much more ultraviolet radiation is reaching the earth's surface.
  Their measurements, taken from the Toronto area (the same latitude
  where Andrew Blaustein conducted his field experiments on amphibian eggs),
  showed what a small change in ozone can mean. Between the winter of
  1989-90 and the winter of 1992-93, ozone in the stratosphere dropped
  by 11 percent, but the amount of UV-B radiation reaching the ground
  climbed by 90 percent. Between the summer months for roughly the same
  period, ozone loss was 7.4 percent, while UV-B radiation increased
  by 30 percent. These increases by seem large, but because the ozone
  layer is so effective at blocking UV-B radiation, a doubling of the
  low natural levels still represents a relatively small exposure." -R.A.

                                        

1 responses total.

The following is from SCIENCE, 23 September 1994. Its good news - if
you have the time.

                 QUICKER OZONE RECOVERY FORECAST

"An international panel of experts has come up with some good news for the
next generation: If ozone-destroying compounds are phased out on the
schedule laid down by the 1987 Montreal Protocol, Earth's protective ozone
layer will return to normal levels in less than 50 years. Earlier
projections had indicated a 75- to 100-year recovery period. The revised
estimate reflects recent studies showing that the atmosphere can clean
itself more rapidly than had previously been supposed. 

"The comeback will still take decades. Although restrictions on some
compounds are already taking hold, the chemicals are entremely long-lived
and will continue to accumulate. The 226 member panel, convened by the
World Meteorological Organization and the United Nations Enviroment
Program, estimates that stratospheric levels of ozone-depleting chlorine
and bromine will peak by around 1998. By then, ozone levels will have
dropped 7% to 13%, depending on the season and latitude, from those of the
late 1960s. These declines would let in 8% to 15% more cancer-causing
ultraviolet radiation than before. 

"The parties to the Montreal Protocol may consider further restrictions at
a meeting next month in Nairobi. According to the panel, a ban on methyl
bromide, an agricultural fumigant, and an accelerated withdrawal of a
chlorofluorocarbon replacement (which still produces some chlorine) could
cut another 15 years off the recovery period."

                                **********

So - keep your hats on...'til 2045.

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