Stratospheric Ozone Depletion
Safe Operating Space
The stratospheric ozone layer protects life on Earth from harmful ultraviolet radiation. The thinning of the ozone layer in the upper atmosphere, primarily due to human-made chemicals, allows more harmful UV radiation to reach Earth's surface. The current total amount of stratospheric ozone is within safe levels, and recovery is ongoing, with values still below mid-20th century levels.
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Importance
If left unchecked, continued human-made Ozone depletion would have created a world where even relatively short exposure to sunshine would have been dangerous to humans, significantly harming plants and animals as well. However, in 1987, a global agreement known as the Montreal Protocol was reached which led to the phasing out of ozone depleting substances such as CFCs and HCFCs. This resulted in the Boundary's status improving and is now back within the safe operating space.
Impacts
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Depletion of stratospheric ozone allows more harmful ultraviolet (UV) radiation to reach Earth's surface, significantly increasing the risk of skin cancer, cataracts, and other health problems in humans. This increased UV radiation also adversely affects terrestrial and aquatic ecosystems. In oceans, it can damage phytoplankton populations, which are crucial for marine food webs. On land, elevated UV levels can impact crop yields and the health of forest ecosystems. Additionally, changes in stratospheric ozone levels influence climate dynamics, as alterations in ozone concentrations affect atmospheric temperatures and circulation patterns, impacting both regional and global climate systems.
Global Map of Recent Ozone Layer Changes
Regional changes in stratospheric ozone concentration between 1979-1989 and 2012-2022 show mixed trends, with increases in some regions and decreases in others, while the persistent Antarctic ozone hole highlights ongoing recovery challenges.
Control Variables
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Stratospheric ozone concentration
The stratospheric ozone layer protects life on Earth from harmful ultraviolet radiation. The extra-polar zone refers to the region of the Earth's atmosphere outside the polar areas, spanning from 60°N to 60°S. While the polar ozone hole is widely known, impacts on humans and ecosystems are more severe in the extra-polar region. Additionally, the ozone hole phenomenon involves complex factors beyond just anthropogenic ozone-depleting substances, making extra-polar ozone a more relevant measure for a Planetary Boundary. While the global stratospheric ozone layer has recovered since the mid-1990s after a significant decline, this recovery may have plateaued in recent years.
Key Drivers
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The primary driver of ozone destruction is a catalytic cycle within the stratosphere involving chlorine. This chlorine is produced through the breakdown of stable chlorofluorocarbons (CFCs) by UV radiation. These stable molecules can persist in the atmosphere for up to a century after being emitted at Earth's surface. Although the Montreal Protocol has successfully controlled CFC emissions, the most significant remaining source of ozone-depleting substances is nitrous oxide (N2O). Agricultural activities are a major source of N2O, contributing to its presence in the atmosphere through various pathways.
Read more about other Boundaries
Planetary Boundary process inside Earth's safe operating space
Planetary Boundary process outside Earth's safe operating space
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