The ozone layer is a natural, protective layer of gas in the stratosphere (the second major layer in the Earth’s atmosphere). It lies approximately 25 miles above Earth’s surface.
Its name comes from the relatively high concentration of ozone (O3) – a highly reactive molecule comprised of three oxygen atoms – present in the layer compared to other parts of the atmosphere, although this concentration is still small in relation to other gases in the stratosphere.
The ozone layer shields life from the Sun’s harmful ultraviolet radiation which can cause skin cancer and cataracts, suppress immune systems and also damage plants.
In 1976, atmospheric research revealed that the ozone layer was being depleted by chemicals containing chlorine and bromine. These include chlorofluorocarbons (CFCs), which were commonly found in air conditioners, refrigerators and spray cans; halons, which are found in fire extinguishers; and methyl bromide, which is used to kill weeds, insects and other pests.
In 1985, researchers at the British Antarctic Survey discovered an ozone hole above Antarctica (later known as the ozone hole). The discovery led to concerns that damage to the layer could threaten life on Earth, leading to increased skin cancer in humans and other ecological problems.
These concerns eventually led to the adoption of the Montreal Protocol in 1987, which bans the production of CFCs, halons and other ozone-depleting chemicals. The ban came into effect in 1989.
As a result of the protocol, ozone levels stabilised by the mid-1990s and began to recover in the 2000s. In 2019, NASA reported that the ozone hole was the smallest ever since it was first discovered in 1982.
Antarctica – the ozone hole
The ozone hole is an annual thin spot that forms in the ozone layer over Antarctica in mid-September and October.
2019 was an unusual year, and saw the smallest ever ozone hole since it was first discovered in 1982. The ozone hole reached its peak extent of 16.4 million sq kilometres on 8 September and then shrank to less 10 million square kilometres for the remainder of September and October.
Arctic ozone hole
Ozone holes rarely form at the North Pole and they are typically short-lived. Temperatures in the Arctic don’t regularly drop as low as they do in Antarctica, which means ozone depletion occurs to a smaller extent. Prior to 2020, the last Arctic ozone hole occurred in 2011.
In late March 2020 scientists spotted signs of a hole forming in the Arctic. The hole reached record dimensions, but by 28 April it was announced that the hole had closed. The rare event was caused by a polar vortex which led to the formation of high-altitude clouds in the region.
Ozone layer and climate change
Many misconceptions exist around the ozone layer. One of the biggest is that the ozone hole drives global warming.
While some extra UV rays from the Sun do slip through the ozone hole, the effect is minimal. In fact, the net effect of the hole is to cool the stratosphere rather than warm the troposphere (the lowest level of the atmosphere that reaches the Earth’s surface). This is because ozone is a greenhouse gas that traps heat, and its destruction therefore has a cooling effect.
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