March 1992 (vol. 8, #3)
1601 N Tucson Blvd #9, Tucson AZ 85716 c 1992
Physicians for Civil Defense
Once the subject of a grade B science-fiction movie, the Blob has reappeared on the news wires and in science journals. This ``Menace of Mass Destruction'' arose from our cherished appliances [refrigerators and air conditioners], just as the ``threat of nuclear annihilation seems to be fading'' (Arizona Republic 2/11/92).
The Blob is made of ``ozone-eating chemicals, principally chlorofluorocarbons, or CFCs [e.g. freon],'' which have been ``found guilty of gnawing a hole in the ozone layer'' (Science 255:797-798, 1992). This winter, ``the blob of high chlorine monoxide slipped off the pole for several weeks in January and hung over northern Europe from London to Moscow'' (ibid., p. 798). Summertime levels of 0.025 parts per billion (ppb) had quadrupled to ``alarming'' levels of 0.100 ppb by December. An all-time high of 1.5 ppb was recorded in January.
According to a NASA prediction,
the Blob could eat between 30 to 40% of the ozone over Canada
this spring. (The natural variability of ozone thickness with
season and latitude is about 25%.) If it does, dire effects are
``Ultraviolet on the Increase''
``It is almost a truism: a loss of stratospheric ozone means there will be more harmful ultraviolet radiation (UV-B) at the Earth's surface,'' announced Paul Crutzen under this headline (Nature 356:104-105, 1992). Friends of the Earth predicted that even one year of continued CFC production could produce hundreds of thousands of skin cancer cases and 10,000 additional deaths in the US alone. A UN report speculated that ozone depletion would speed the progression of AIDS by an as-yet-unknown mechanism, ``although ultraviolet rays would not necessarily increase the rate of infection'' (AP).
Warning people about the predicted ozone depletion, the Canadian environment minister urged people not to panic, but to keep their children out of the sun and to wear sunglasses, a hat, and sunscreen, even on balmy spring days when the temperature reaches -3 C.
Contradicting his own headline, Crutzen observes that less ozone does not necessarily mean more UV-B. Sulfate particles, tropospheric ozone due to air pollution, and even cloudiness tend to decrease ultraviolet levels. Crutzen reports on a theoretical method of calculating UV-B levels. The maximum increase in dose in the Antarctic spring is estimated to be only 7% of the total typically received at the Equator.
Crutzen concludes that we need
a worldwide network of UV-B monitoring stations so that we can
substitute measurements for calculations. (Actually, measurements
were made between 1974 and 1986, but were discontinued due to
cost. They showed decreasing penetration by ultraviolet radiation,
according to Dixy Lee Ray in Trashing the Planet.)
Is Ozone on the Decrease?
The ozone decrease is a prediction of a computer model involving complex photochemistry and atmospheric dynamics, including stratospheric clouds that form only under special conditions in the Antarctic cold (Sci Amer, June, 1991). The nuclear winter hypothesis was also based on a computer model. Carl Sagan's prediction from that model a global climatic catastrophe caused by oil fires in Kuwait was recently tested.
To test the ozone model, we
need satellite measurements of stratospheric ozone, which have
become available only recently: the jagged line in the figure
below. Obviously, the ozone levels fluctutate wildly. To use
these data to ``show'' an ozone depletion justifying Draconian
controls on CFCs, the EPA drew the dotted line. However, the
authors of the report identified a rising trend in ozone after
the time of the solar minimum in 1986 (the solid lines in the
figure were drawn by Petr Beckmann). Since ozone is formed through
photochemical reactions, it is reasonable to expect that levels
should correlate with solar activity; however, data are available
for only one solar cycle.
Satellite measurements of ozone
levels, reprinted from Access to Energy, July 1991.
Banning the Blob
An international accord called the Montreal Protocol bans CFCs by the year 2000. Based on alarming forecasts (which were not submitted to peer review) and a presumption of CFC guilt, European environment ministers hastened to announce earlier bans. President Bush ordered the end of US production by 1995.
How will the ban affect the atmosphere? We don't know. Even if chlorine atoms lead to ozone depletion, the relative contributions of Mt. Pinatubo and CFCs are not known because radioactive tracer studies have not been done. Michael Kurylo of NASA thinks that an early CFC phaseout will reduce stratospheric chlorine by a few tenths of a ppb from a predicted high of 4.1 ppb (Science, op. cit.).
There is no time to wait for data. The Blob might be ready to engulf us. Science can't prove that it isn't.