Planetary boundaries: how we saved the ozone layer
The ozone layer protects all forms of life on Earth from hazardous ultraviolet radiation. In 1985, scientists noticed that this protective shield had become considerably thinner over the Antarctic. The cause of what became known as the “ozone hole” was chlorofluorocarbons (CFCs), a group of chemicals that can also be harmful to the climate. The international community acted quickly and succeeded in phasing them out. Today the ozone layer is gradually recovering.
Without the ozone layer in the upper atmosphere, chances for life on Earth would be bleak. This is because, in addition to the light we see, the Sun also emits energetic and short-wavelength ultraviolet radiation that is invisible to the human eye. This UV radiation can damage cells and destroy the DNA of living things. It also damages ecosystems in the ocean and on land and can cause skin cancer in humans.
The ozone layer is in the stratosphere at a height of 15 to 50 kilometers and contains about 90 percent of the atmosphere’s ozone. Ozone absorbs a portion of the Sun’s UV radiation that would be dangerous to living things. Scientists noticed in the 1980s that the ozone layer was becoming depleted, especially over the Antarctic around the South Pole. This increased the risks associated with higher UV radiation.
The ozone hole: a planetary emergency was averted
The ozone hole was caused by substances known as chlorofluorocarbons (CFCs), which can damage ozone. Researchers had already discovered in the 1970s that these substances, which were used in refrigerators and spray cans, can destroy ozone.
There is a special kind of polar clouds in the stratosphere over the Antarctic. If chlorine compounds from decomposed CFCs come into contact with these clouds, chemical reactions between the chlorine compounds and ozone will degrade the ozone. Ozone depletion was also detected around the North Pole, in the Arctic, in the 1980s, though it was not as severe.
Fortunately, the international community acted very quickly once it became clear what was happening. National representatives met in Canada and agreed to reduce CFCs. The 1987 Montreal Protocol and its subsequent agreements resulted in a near-total shutdown in the production of these hazardous chemicals. This major political success prevented us from overstepping this boundary. A further increase in ultraviolet radiation on the ground would have had severe consequences for humanity, animals and plants.
How can we stay on the right path?
Quick action kept the world from overstepping the boundaries of the ozone layer. If all countries continue to honor their commitments under the Montreal Protocol, the ozone hole will disappear completely some day. However, since the CFCs have an atmospheric lifetime of 50 to 100 years, the ozone layer’s recovery will continue into the second half of this century.
The Montreal Protocol was also a triumph of climate action
Today the Montreal Protocol and its subsequent agreements regulate the use of ozone-destroying substances like CFCs and their replacements. Some of these substances not only destroy ozone, they also have a high global warming potential, which means they can trap heat in the atmosphere and contribute to the global rise in temperatures. By banning ozone-damaging chemicals, policymakers not only rescued the ozone layer, they also helped protect the climate.
There are still arctic winters with considerable ozone depletion. Scientists believe that the rise in CO2, which leads to higher temperatures on the ground, cools the stratosphere and probably has increased Arctic ozone losses in recent years.
Scientific editing: Jens-Uwe Grooß, Forschungszentrum Jülich
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