Depletion of the Ozone Layer
and the Montreal Protocol to ban CFCs:
Recognition of the problem:
During 1973, two chemists at the University of California, Irvine -- Frank Rowland and Mario Molina -- were studying the effects of Chlorofluorocarbons (CFCs) on the atmosphere. CFC's are gasses that were widely used at the time in aerosol spray cans, fire suppression systems, air conditioners, refrigerators, etc. The team found that CFC's were amazingly stable. Once released, they would drift upwards through the atmosphere until they reach the stratosphere between about 6 and 30 miles above the Earth's surface. They reach the middle of the stratosphere after about five to ten decades, where they were finally broken down by ultraviolet radiation from the Sun. This releases chlorine. The chlorine, in turn, breaks down the ozone gas (O3) that naturally occurs in the stratosphere.
One of the main effects of ozone is to adsorb ultraviolet-B (UV-B) radiation from outer space. Higher levels of UV-B would increase the incidence of human eye cataracts which, if untreated, can lead to blindness. It would also cause a decrease in people's immune systems,:
"... an increase in skin cancer, and other impacts such as damage to crops and to marine phytoplankton." 1
Rowland and Molina testified before the federal House of Representatives in late 1974. The federal government later funded research into the problem. In 1976, the National Academy of Sciences (NAS) released the first of its many reports, confirming that ozone depletion by CFC was a real, serious, and growing phenomenon with long-term consequences.
During 1985, scientists Joe Farman, Brian Gardiner and Jonathan Shanklin published a paper describing their observations of unusually low levels of ozone in the atmosphere at the Caird Coast, Antarctica, near the South Pole. This became universally known as the "ozone hole." There is no actual "hole" -- only a thinning of the concentration of ozone over a very large area.
That same year, the Vienna Convention was signed by twenty countries. It called for international regulations restricting gasses capable of depleting the ozone layer. During 1987-SEP, the Montreal Protocol was signed by 46 nations. Its goal is:
"... to protect the ozone layer by taking measures to control total global production and consumption of substances that deplete it, with the ultimate objective of their elimination on the basis of developments in scientific knowledge and technological information." 2
The Montreal Protocol entered into force on 1989-JAN-01. Over time, all of the members of the United Nations along with Niue, the Cook Islands, the Holy See, and the European Union have ratified the agreement. The Vienna and Montreal agreements became the first treaties to be ratified by all members of the UN. Kofi Annan, the 7th Secretary-General of the United Nations between 1997 and 2006, referred to the Montreal Protocol as:
"perhaps the single most successful international agreement to date." 2
Concentration of CFC's in the stratosphere reached a maximum circa 1999 and has begun a slow decline. In response, ozone losses stabilized and have now begun to decline. 7
The "ozone hole" over the Antarctic:
This image represents the largest "hole" in the ozone layer over the Antarctic ever measured. It is not a photograph. It was created from successive scans of the area by satellites in late 2006-SEP. The area of the "hole" was 11.4 million square miles or 29.5 million square kilometers. This is almost three times the area of the 48 contiguous U.S. states and DC. The purple-shaded area in the center is the location of the greatest ozone depletion. Blue, green and yellow-shaded areas have progressively higher levels of ozone remaining.
The chemical reactions that destroy the ozone are:
"... most effective when they occur on the surface of ice crystals, in the stratosphere. There are more ice crystals when it is most cold.
Antarctica is colder than the Arctic circle because the ratio of land to water is higher.
Therefore ozone depletion over the South Pole is greater than ozone depletion over the North Pole." 4
The "ozone hole" in the Arctic is much smaller. It is referred to as the "ozone dimple." 4
The "holes" in the Arctic and Antarctic are not going away anytime soon. CFCs that were produced in the 1970's and 1980's are still present in the stratosphere, breaking down the ozone. It will take decades before all the CFCs break down and dissipate.
Kathryn Mersmann, at NASA's Goddard Space Flight Center, wrote:
"Scientists expect the Antarctic ozone hole to recover back to 1980 levels around 2070. ... NASA and NOAA monitor the ozone hole via three complementary instrumental methods. Satellites, like NASA’s Aura satellite and NASA-NOAA Suomi National Polar-orbiting Partnership satellite measure ozone from space. The Aura satellite’s Microwave Limb Sounder also measures certain chlorine-containing gases, providing estimates of total chlorine levels." 5
The "hole" reaches its annual maximum each year near the end of winter in the Southern Hemisphere. For the year 2017, this occurred on SEP-11:
Two additional items:
At their meeting on 2016-OCT-15, parties to the Montreal Protocol on Substances that Deplete the Ozone Layer agreed to also phase-out the use of hydrofluorocarbons (HFC's).
SEP-16 eacy year is the International Day for the Preservation of the Ozone Layer. 8
Why has the ozone problem been brought under control, whereas climate change has not?"
There are a number of reasons:
Replacement chemicals were available, and could immediately replace CFCs.
There were only a few manufacturing plants of CFC's in the world to control.
The cause and effect relationship between CFC's, chlorine, and ozone was scientifically well known, proven, and accepted.
There is a long, multiple decade, delay between stopping the use of CFC's and the restoration of the ozone layer. Thus, it was important to take action quickly.
The following information sources were used to prepare and update the above
essay. The hyperlinks are not necessarily still active today.