The ozone layer is a thin shield of gas in the upper atmosphere that absorbs the sun’s most dangerous ultraviolet radiation before it reaches Earth’s surface. Without it, UV levels would be high enough to cause widespread skin cancer, destroy marine food chains, and damage crops. It is, in practical terms, what makes life on land possible.
How Ozone Blocks Ultraviolet Radiation
Ozone sits in the stratosphere, roughly 15 to 35 kilometers above the ground. The molecule is made of three oxygen atoms, and its structure makes it exceptionally good at absorbing ultraviolet light. It filters out virtually all UV-C radiation (wavelengths between 100 and 280 nanometers), which is the most energetic and biologically destructive type. It also absorbs a large portion of UV-B radiation (280 to 315 nanometers), which is the primary cause of sunburn and skin cancer in humans.
The higher-energy portion of UV-B, between 280 and 295 nanometers, never reaches the ground at all thanks to this filtering. What does get through is a reduced amount of UV-B and most UV-A, which is the least harmful type. Even small changes in ozone concentration shift the balance significantly. Without the international agreement to protect the ozone layer (the Montreal Protocol), sunburning UV levels at latitudes below 50 degrees would have increased by 10 to 20 percent between 1996 and 2020 alone.
Protection Against Skin Cancer and Eye Damage
The health stakes are enormous. Overexposure to UV radiation causes three types of skin cancer: melanoma, squamous cell carcinoma, and basal cell carcinoma. It also damages the eyes, causing cataracts and cancers of the cornea and conjunctiva. UV exposure even suppresses the immune system in ways that can compromise your body’s ability to fight disease.
Modeling by U.S. researchers put hard numbers on what ozone protection actually prevents. Compared with a scenario where no controls on ozone-depleting chemicals were ever enacted, the Montreal Protocol is estimated to prevent 443 million cases of skin cancer and 63 million cataract cases among people born in the United States between 1890 and 2100. That includes 2.3 million skin cancer deaths avoided. Even the strengthened amendments to the original 1987 agreement, on their own, account for an additional 230 million fewer skin cancer cases and 33 million fewer cataract cases beyond what the first version would have achieved.
These are not abstract projections. They reflect the direct relationship between ozone thickness and the amount of UV-B reaching your skin. Every percentage point of ozone lost translates into measurably more radiation at ground level, and measurably more cancer over time.
Why Oceans and Food Chains Depend on It
The ozone layer protects far more than human skin. Phytoplankton, the microscopic organisms floating near the ocean’s surface, form the base of the marine food web and produce a significant share of the world’s oxygen. They are highly sensitive to UV-B radiation.
Research in the southeast Pacific Ocean found that enhanced UV-B caused a 34 percent drop in primary production (the rate at which phytoplankton convert sunlight into energy) in surface waters. The damage gets worse at higher latitudes, where ozone depletion is most severe. Models estimate that a 16 percent decrease in stratospheric ozone would cause roughly 20 percent of near-surface phytoplankton species in a given ecosystem to lose half their photosynthetic capacity. At high southern latitudes, near-surface ocean productivity could fall by more than 32 percent.
This matters because phytoplankton are not just food for tiny marine organisms. They support the entire chain, from zooplankton to fish to seabirds and marine mammals. A sustained drop in primary production would reduce fisheries yields globally, threatening both ocean ecosystems and the human food supply that depends on them.
Effects on Agriculture and Materials
Crops are vulnerable to UV-B as well. Higher UV exposure reduces plant growth, lowers yields, and can alter the nutritional quality of food. The ozone layer’s filtering effect keeps UV-B within a range that most agricultural species can tolerate. Without it, farming at scale would require entirely different approaches.
Synthetic materials also degrade faster under intense UV radiation. Polymers used in outdoor infrastructure, from building materials to vehicle components, break down when exposed to high-energy UV wavelengths. The stratosphere’s filtering of the most damaging UV-B wavelengths (280 to 295 nanometers) slows this degradation considerably, extending the useful life of materials that modern economies depend on.
Good Ozone vs. Bad Ozone
There is an important distinction between ozone in the stratosphere and ozone at ground level. Stratospheric ozone is protective. Ground-level ozone is a pollutant.
Ozone near the surface forms when sunlight reacts with emissions from vehicles, power plants, and industrial activity. It is a key ingredient in photochemical smog. Breathing it causes respiratory and cardiovascular problems, and it contributes to several million premature deaths per year globally. It also damages forests and reduces crop yields.
Interestingly, the two are connected. UV radiation drives the chemical reactions that create ground-level ozone. By preventing the worst ozone depletion in the stratosphere, the Montreal Protocol also avoided large increases in surface-level UV that would have worsened air pollution in cities. Protecting the ozone layer up high, in other words, also helped limit the harmful ozone down low.
Current Recovery and Timeline
The ozone layer was severely damaged by human-made chemicals, particularly chlorofluorocarbons (CFCs), used in refrigerants, aerosol sprays, and industrial applications from the mid-20th century onward. The Antarctic ozone hole, first identified in the 1980s, became the most visible symbol of that damage. NASA defines the hole as any area where total ozone drops below 220 Dobson Units, a threshold never seen in historic observations over Antarctica before 1979.
The Montreal Protocol, signed in 1987 and strengthened multiple times since, phased out the worst of these chemicals. The results are measurable. The 2025 Antarctic ozone hole was notably small and short-lived, confirming a long-term recovery trend. According to the World Meteorological Organization’s most recent assessment, the ozone layer is expected to return to 1980 levels by around 2040 for most of the world, by 2045 over the Arctic, and by approximately 2066 over the Antarctic, where depletion was most extreme.
Year-to-year fluctuations still occur, driven by stratospheric temperatures and volcanic activity, but the underlying trend is clear. The ozone layer is healing, and with it, the planet retains the UV shield that ecosystems, agriculture, and human health all require to function.