Ultraviolet (UV) radiation / Ozone Frequently Asked Questions

Ultraviolet radiation

What is ultraviolet (UV) radiation?

Ultraviolet (UV) radiation is a type of energy produced by the sun. It is different to the sun’s light (which we see) and the sun’s heat (which we feel). The sun emits three bands of energy: UVA, UVB and UVC. The stratosphere blocks all UVC radiation, most UVB but none of the UVA radiation. Therefore both UVA and UVB are of interest for human health. They contribute to skin damage, premature ageing, and skin cancer.

Knowing about UV is very important for our lives under the Australian sun. We have one of the highest levels of UV exposure and highest rates of skin cancer in the world.

SunSmart sun and UV
How harmful is UV radiation?

Too much UV to the skin in a short period can cause painful sunburn, and numerous sunburns cause lasting damage to the skin. People exposed to UV without any protection over many years suffer irreparable damage. This comes in the form of premature ageing, eye damage, skin damage and in the worst case, skin cancer.

Premature ageing

The first sign of skin damage from UV is premature skin ageing in people under 50. Sun-exposed skin especially on the face, forearms and backs of the hands, becomes wrinkled and dry, often with brown spots and on the face, small visible blood vessels. These changes result from UV destroying the elasticity that gives skin its youthful appearance. You can tell the amount of UV damage to exposed skin simply by comparing its appearance and texture with skin that doesn’t see the sun.

Eye damage

It’s not just your skin that suffers. UV also harms our eyes when they are unprotected from the sun for many years. It causes growth of tissue and blood vessels in the inner corners of the eyes (called 'pterygium') and cataracts in the lens of the eye.

Skin cancer

Severe UV damage to skin cells results in red, scaly skin lesions (sometimes known as 'sunspots'). In time, skin cancers may develop from the damaged cells. In fact, skin cancers are by far the most common cancers in Australia. Your face is most often affected, and the scalp, if unprotected by hair or a hat, is also very prone to UV damage and skin lesions.

There are several types of skin cancers, which vary in severity. Melanoma is a less common form of cancer that arises in the skin’s pigment cells. It is the most dangerous skin cancer and looks like a brown or black mole that is changing in size or colour, though very occasionally a melanoma may appear red or pink. Australia and New Zealand have the highest melanoma rates in the world. Melanoma is preventable by protecting the skin from UV, starting in childhood.

What factors affect the amount of UV radiation that reaches the Earth?
  • Air pollution: Urban smog can reduce the amount of UV by reflecting UV back towards space or absorbing it.
  • Bushfire smoke: Bushfire smoke can absorb and reflect incoming radiation and reduce UV levels. The thicker the smoke, the greater the reduction in UV. UV levels can still be harmful, particularly during the height of summer when many bushfires occur.
  • Altitude: The air is thinner and usually cleaner at higher altitudes over mountains. With less absorbing atmosphere available, more UV reaches the Earth's surface.
  • Cloud cover: Cloud cover, especially thick unbroken clouds and rainfall can reduce UV, as thick clouds reflect and absorb more UV than thin cloud cover. However, the sides of clouds can also reflect UV and increase the amount of UV at the Earth's surface.
  • Latitude: The most intense radiation is found when the sun is directly overhead so this is at the equator in the spring and autumn, at the Tropic of Cancer in the northern hemisphere summer and at the Tropic of Capricorn in the southern hemisphere summer.
  • Ozone: Less ozone in the atmosphere leads to higher UV levels, and vice versa.
  • Time of day: On any day the greatest amount of UV reaches the Earth around midday when the sun is at its highest point. When the sun is low in the sky, solar energy must travel a greater distance through the atmosphere and more UV is scattered and absorbed.
  • Time of year: UV changes throughout the year. The highest levels are in summer months, and lowest levels in winter months.
Is there any link between the temperature and UV levels?

UV levels are not related to how hot or cold the temperature is. There are differences between UV levels during summer and winter, but this is mostly due to the angle of the sun in the sky. UV levels generally peak around the middle of the day, while the temperature may still be rising towards its maximum in the afternoon.

A graph showing the relationship between temperature
and UV index between sunrise and sun set in Melbourne
on the 5th of January 2008. The Y axis on the left
shows the temperature in degrees Celsius from 20 to 40
degrees. The X axis (across the bottom) give the time
of day between sunrise at 6 in the morning and sunset
at 9 at night. The Y axis on the right show the UV index
between zero and 15. A blue line representing the UV index
shows that it is at 0 at sunrise and sunset, and at 3 at
approximately 9 in the morning and 5 in the afternoon and
peeks at 12 at 1 in the afternoon. The temperature,
represented by a red line, on the other hand, starts at
about 22 degrees at 6 in the morning and slowly climbs to
a peek of around 37 degrees at about 7 in the evening then
falls to about 32 degrees at 9 at night.
How does snow and water affect UV levels?

Snow and water are highly reflective, increasing the amount of UV you are exposed to.

Sitting under a shade structure on the beach for long periods might protect you from the direct effects of the sun, but you’ll still be exposed to UV. If you’re sitting on the beach you’ll get an extra 20 per cent of UV reflected from the dry sand. On a boat, you'll get an extra 10 per cent reflected from the water, and another 10 per cent reflected from your boat.

Despite the cooler temperatures, UV can actually be more dangerous for visitors to Australia's alpine regions. More UV reaches the earth's surface in the mountains because the atmosphere is thinner the higher up you are. Snow increases UV levels by approximately 90% for fresh snow and 50% for old snow. Sun protection is recommended by Cancer Council Australia while at the snow.

How does UV exposure change during the year?

UV levels change throughout the year in line with the seasons. The highest exposure levels are experienced in the summer months, and the lowest levels in the winter months. During spring and autumn, UV levels may change rapidly day to day. View our climatology maps for more detailed information.

How does UV exposure change by location?

People in many parts of Australia require sun protection all year round. The closer to the equator you are, the higher the UV radiation level. People in Darwin and Brisbane need sun protection throughout the year. It is best to check the UV Index and times of day you need sun protection for your exact location. If you are travelling, remember that UV may be different depending on your location.

The World Health Organisation has compiled a list of countries that provide UV forecasts.


What is ozone?

Ozone is the triatomic form of oxygen (that is O3 rather than the usual form O2) and is a naturally occurring trace gas in the earth's atmosphere.

Where is ozone found in the atmosphere?

About 90% of ozone is concentrated in the lower part of the stratosphere, between about 15 and 30 kilometres above the earth's surface, where it is sometimes referred to as the ozone layer. Ozone is also found naturally, at lower concentrations, in the troposphere. In the boundary layer, human made pollutants can cause the production of excess ozone.

Ozone is found in the atmosphere over the entire globe although the amount varies with location and season.

Why is ozone important?

Ozone is the major absorber of UVB (Ultraviolet radiant energy in the wavelength range 280-320 nanometres) in sunlight, absorbing approximately 90% of it. Many experimental studies of plants and animals, and clinical studies of humans, have shown the harmful effect of excessive exposure to UVB radiant energy. In humans these effects include increased incidence of skin cancer and cataracts.

In the 1970s, scientists first raised concerns that the production and use of synthetic substances known as chloroflourocarbons (CFCs) might lead to a reduction of ozone in the stratosphere leading to an increase of UVB radiant energy. It was with the discovery of the Antarctic Ozone Hole, however, in the mid 1980s, that the issue of ozone depletion due to human activity rose to great prominence, leading to the signing of the Montreal Protocol.

Ozone is also a radiatively important gas in the atmosphere which absorbs both incoming ultraviolet and outgoing infrared radiant energy, and thus has a significant impact on the earths climate.

Finally, ozone remains a very useful tracer for following air movements in the stratosphere in fact this is the reason it was originally monitored.

In the troposphere, excess ozone is generated by human pollution and is harmful to human, animal and plant health.

What is meant by ozone depletion?

During the 1980s and early 1990s, ozone levels around the world dropped steadily, and scientists believe this reduction was primarily due to the human production of Ozone Depleting Substances (ODSs). Averaged over the globe, the size of the reduction was approximately 5%, although this amount varied considerably with location and season.

However, it was also discovered in the mid 1980s that a much greater depletion of ozone had started taking place each year over Antarctica in springtime, and this phenomenon became known as the Antarctic Ozone Hole and received great publicity.

During the most severe period of the Antarctic Ozone Hole (usually late September or early October) total column ozone can drop by as much as a half or even two-thirds at some locations.

The Antarctic Ozone Hole has continued to form each year from the 1980s until today.

What are Ozone Depleting Substances?

Ozone Depleting Substances (ODSs) are gases that contain chlorine or bromine atoms in forms able to reach the stratosphere, where they can take part in chemical reactions that destroy ozone on a large scale. The best known are the chloroflourocarbons (CFCs), formerly used extensively in refrigeration, air-conditioning, foam-blowing and as aerosol propellants, and the halons (hydrocarbon gases containing bromine), which were widely used as fire extinguishers. Production of all major ODSs is now regulated by the Montreal Protocol. Most ODSs are made by human activity but some do have natural sources as well, including methyl bromide and methyl chloride.

How much has ozone been depleted over Australia?

Ozone depletion in the 1980s and early 1990s was more severe in the southern hemisphere than the northern. Observations suggest that, in southern mid-latitudes (which includes Sydney, Canberra, Adelaide, Melbourne and Hobart) the amount of depletion caused by ODSs during this time was about 5%. The amount of depletion was observed to be smallest in the tropics and to increase with distance from the equator. It is important to remember, though, that total ozone varies considerably from year to year due to natural variations, not all of which are currently fully accounted for. This means that it takes many years for clear trends to be discernible. Further long-term ozone changes can be caused by changes in transport rather than chemistry. Nonetheless, there are now tentative early indications that ozone is recovering following the success of the Montreal Protocol and its amendments.

Is ozone depletion the same as the greenhouse effect, global warming or climate change?

Ozone depletion and changes to climate due to the increased concentration of well-mixed greenhouse gases produced by human activity are essentially separate issues, in the sense that either one would still occur in the absence of the other, however they do interact with each other in numerous ways. Ozone is itself a greenhouse gas and there is evidence that stratospheric ozone depletion has had an impact on tropospheric weather patterns. Many of the substances regulated by the Montreal Protocol are also strong greenhouse gases. Conversely, the rate at which ODSs deplete ozone is heavily dependent on the state of the atmosphere including stratospheric temperature and circulation speeds. For example, cooler temperatures in the Antarctic stratosphere would lead to an increase in severity of the Antarctic Ozone Hole. Many of these linkages are not currently well understood and are the subject of current research.

Antarctic Ozone Hole

What is the Antarctic Ozone Hole?

The Antarctic Ozone Hole refers to a severe depletion of ozone which has been observed to take place over Antarctica in springtime every year since the early 1980s. The standard definition is the region where the total column ozone is less than 220 Dobson Units (DU).

It should be kept in mind that the word hole does not imply there is no ozone at all over a particular point.

When did the Antarctic Ozone Hole first appear?

In the early 1980s, the British Antarctic Survey noticed that springtime ozone values measured by their Dobson spectrometer at Halley since 1958 had been dropping since the 1970s. The Japanese station at Syowa also measured decreases in ozone. In 1985, the decreases over Halley were reported in a now-famous article by Farman, Gardiner and Shanklin published in the journal Nature. Satellite observations then revealed that the depletion was actually taking place over a wide area across Antarctica, and the term ozone hole came into widespread use.

When does the Antarctic Ozone Hole occur?

In each year, the Antarctic Ozone Hole typically first appears in August, reaches a peak size in late September and dissipates in mid-December, although there is some variability in this timing from year to year.

How large is the Antarctic Ozone Hole?

The maximum size of the Antarctic Ozone Hole reached each year increased rapidly from the early 1980s up until the early 1990s. Since then, however, the maximum area each year has almost always been in between 25 and 30 million square kilometres, the exceptions being the years 2002 and 2004 where it was somewhat less. (For comparison, the area of Australia is 7.7 million square kilometres). The largest areas so far observed have been 30 million square kilometres in 2000 and 29 in 2006. The years 1998, 2003 and 2005 also saw very large holes form.

What causes the Antarctic Ozone Hole to form?

Three essential ingredients are necessary for the Antarctic Ozone Hole to form: ozone depleting substances, cold temperatures and sunlight. Ozone depleting substances were produced in industrial areas all over the world but over the course of many years, make their way into the stratosphere and are eventually transported to the polar regions. While the stratosphere is very dry, at very cold temperature (below -78C), clouds can nonetheless form, known as Polar Stratospheric Clouds (PSCs). PSCs form over a large area of Antarctica during winter. On the surface of these clouds, chemical reactions take place which convert chlorine and bromine into highly reactive forms, which in the presence of sunlight, undergo further reactions which are able to destroy vast numbers of ozone molecules. The Antarctic Ozone Hole thus appears when sunlight returns to Antarctica at the end of winter.

Why does the Ozone Hole only occur over Antarctica?

The chemical reactions that lead to the formation of the Antarctic Ozone Hole take place on the surface of Polar Stratospheric Clouds (PSCs), which can only form in very cold conditions (-78C). Because of differences in the geography of the northern and southern hemispheres, the temperature over Antarctica in winter is somewhat colder than over the Arctic, resulting in PSCs being able to form over a much greater area and for a longer duration. This is the main reason why ozone depletion in the Arctic, while significant, does not result in a sustained ozone hole forming.

Does the Antarctic Ozone Hole ever come over Australia?

No. The ozone hole has only ever been observed to be well south of the Australian mainland and Tasmania. In fact, during springtime, when the hole is in existence, ozone levels over southern Australian cities are at their highest.

However, after the ozone hole has broken up parcels of ozone depleted air mixed with mid latitude air move northwards. These parcels can move over the southern part of Australia and cause a reduction in total ozone values.

When will the Antarctic Ozone Hole recover?

The latest calculations suggest that Antarctic ozone will recover to 1980 levels around the period 2055-2080, assuming the Montreal Protocol continues to be strictly observed.

How are ozone levels measured?

Australia takes part in the Global Atmosphere Watch (GAW) international monitoring and research program coordinated by the World Meteorological Organization (WMO). The Bureau operates a network of ozone monitoring stations (at Melbourne, Brisbane, Darwin, and Macquarie Island), where the total amount of ozone above the station (total column ozone) is measured several times every day.

The total column ozone is measured with an instrument called a Dobson spectrophotometer, which compares the amount of sunlight at two ultraviolet wavelengths, one wavelength being strongly affected by ozone and the other one not. Total column ozone can then be calculated from the difference in the sunlight measured at the two wavelengths.

The Bureau also flies ozonesondes weekly from Macquarie Island and Melbourne (using the Bureaus training annexe at Broadmeadows), as well as a partial program at Davis in Antarctica funded in part by the Australian Antarctic Division. Ozonesondes are devices which measure the ozone concentration in air electro-chemically. Carried into the air by a hydrogen balloon, they are then able to determine the ozone profile at high resolution from the ground up to a height of as great as 35 kilometres.

Since the late 1970s the ground-based networks have been supplemented by satellite instruments which are able to measure total ozone and to a certain extent, ozone profile, at high temporal and spatial resolution. The global ground-based network is still essential however to provide a reliable and well-calibrated long-term record.

What is a Dobson unit?

Ozone is measured in Dobson Units (DU). 300 DU is equivalent to a 3 millimetre thick layer of pure ozone at sea level temperature and pressure. The Dobson Unit is named after G.M.B. Dobson, the English physicist who pioneered the study of stratospheric ozone.

How long has ozone been measured in Australia?

The CSIRO began ozone measurements in Melbourne in 1956 in cooperation with the Bureau of Meteorology and in 1982 total responsibility passed to the Bureau.

What is the Montreal Protocol?

After the discovery of the Antarctic Ozone Hole, governments around the world moved quickly to adopt the Vienna Convention for the Protection of the Ozone Layer in March 1985. Work then began on negotiating a protocol to control the production and use of ozone depleting substances across the world, leading to the adoption of the Montreal Protocol on 16th September 1987, now celebrated as The International Day for the Preservation of the Ozone Layer. Since then, a number of Amendments to the original agreement have also been adopted to hasten the phasing-out of ODSs and to increase the number of substances controlled by the Protocol. To date, the Montreal Protocol has been ratified by one hundred and ninety three countries.

Has the Montreal Protocol been effective?

Yes. By 2006 consumption of ODSs globally had been reduced by over 96% compared to 1986 levels. Although the atmospheric lifetimes of many ODSs are very long (greater than a hundred years in some cases), the total concentration measured in the troposphere has now been declining since the mid 1990s.

How can I stay updated with the latest news about the ozone hole?

The World Meteorological Organization (WMO) puts out regular Antartica Ozone Bulletins.

More information can be found from the following organisations:

Map legend:
      11+ (violet) extreme,
      8-10 (red) very high,
      6-7 (orange) high,
      3-5 (yellow) moderate,
      1-2 (green) low
      Protect yourself in 5 ways:
      1) Slip on sun-protective clothing, 
      2) Slop on SPF30+ sunscreen. Reapply every two hours, 
      3) Slap on a broad-brimmed hat, 
      4) Seek shade, 
      5) Slide on wrap-around sunglasses.

Check and protect

It is important for all Australians and visitors to look and listen for UV Index levels in local weather forecasts. Use a combination of sun protection measures – never rely on just one.

Think UV, not heat

UV radiation is not related to how hot or cold it is. You can still get burnt on cool or cloudy days.

Other information