In 1974, U.S. chemists Sherwood Rowland and Mario Molina were the first to sound the alarm. That year, they published the first scientific article predicting the near disappearance of the ozone layer in 75 years. They were remarkably prescient; in the early 1980s, a hole in the ozone layer was observed for the first time at the Earth's poles. And the numbers were frightening. Over the Antarctic, 70% of the protective gas had disappeared, while 30% had been depleted over the Arctic. Rowland and Sherwood won the Nobel Prize in chemistry in 1995 for their work in atmospheric chemistry.
In recent decades, concern about the deterioration of the ozone layer has been growing. In the late 1980s, the Montréal Protocol on Substances that Deplete the Ozone Layer was signed with the goal of gradually eliminating the use of various substances, in particular CFCs. The Protocol was ratified in 1987 by Canada, the European Economic Community and 28 other countries.
Since then, a number of other countries have come on board, bringing the total number of signatory countries to 175.
How are things looking at the start of the third millennium? Controlling ozone-depleting substances has helped enormously, but the battle is far from over. In 1996, 1997 and 2000, observations showed a strong depletion of the ozone layer over the Arctic, by as much as 60% in some layers of the atmosphere. In the lower stratosphere, near the South Pole, the hole reached a record size in spring 2000, measuring 28.3 million kilometres. The affected area extended to the southern tip of South America.
In 2003, Canada launched SCISAT. The mission of the scientific satellite is to study the ozone layer, with special emphasis on changes occurring over Canada and the Arctic. SCISAT findings will be used to forecast the ozone layer's future behaviour and improve understanding of the mechanisms causing its depletion.
Canada is also participating in the OSIRIS mission. This scientific instrument aboard the Swedish satellite Odin that was launched in 2001 is different from other scientific missions. It uses sunlight to capture the signature of the ozone column that it travels through. Through observations of the atmospheric limb, it is possible to record ozone distribution. The OSIRIS mission will continue until early 2005, and perhaps even beyond.
Data on the ozone layer collected by OSIRIS, SCISAT and NASA's new satellite AURA will help measure the impact of international environmental initiatives, such as the Montréal Protocol. Once decision makers and the public are better informed, they will be able to continue and adapt their efforts to preserve Earth's protective ozone layer.
Visit the Environment Canada Web site to learn more about the ozone layer.
Pages on SCISAT provide more information on the Canadian satellite's mission.
An article published in Apogee , the electronic newsletter, explains the OSIRIS mission in an interview with Ted Llewellyn, who is in charge of the Canadian component of the mission.