![]() We expect the ozone layer to slowly recover from the impact of CFCs, which is likely to reduce UV levels. It’s harder to say what will happen in the future, as there are several uncertain factors. A NASA study found similar results for 1979 to 2008. In Australia, a study in 2011 found the average UV index had increased by 2 to 6 per cent between the 1970s and the period 1990 to 2009, due to depletion of the ozone layer. We know UV levels have increased in recent decades. While this makes the air nicer to breathe, pollution does absorb or block some UV radiation. And finally, the air in Australia generally has less smoke, dust and other small particle pollution than many places in the northern hemisphere. This was caused by the use of chemicals called chlorofluorocarbons or CFCs, and it has been improving since they were banned by an international agreement in 1987. The layer of ozone in the upper atmosphere, which absorbs some UV-B, is thinner towards the South Pole. A third reason is the ‘hole’ in the ozone layer. Another is that Earth is very slightly closer to the Sun in the southern hemisphere’s summer than the northern summer, meaning the sunlight is a few percent brighter. One is that Australia’s cities are closer to the Equator than many big cities in Europe and North America. Read more | New research: Ultraviolet levels and the risk of death from Covid-19 (Shorter wavelengths are called UV-C, but are mainly blocked by the atmosphere so we don’t need to worry about it.) There are two important kinds of UV radiation: UV-A, with wavelengths from 400 to 315 nanometres, and UV-B with wavelengths from 315 to 280 nanometres. An important part of the spectrum is ultraviolet or UV radiation: light with wavelengths too short for our eyes to see, from around 400 nanometres to 10 nanometres. The Sun showers Earth with light at a huge spectrum of different wavelengths, and each wavelength can have a slightly different effect on human skin. A score of 1 or 2 is low, 3 to 5 is moderate, 6 or 7 is high, 8 to 10 is very high, and 11 and above is extreme. The index boils down several factors into a single number that gives you an idea of how careful you need to be in the sun. In 2002, the World Health Organisation devised the UV index in an effort to make people around the world more aware of the risks. ![]() Read more | Explained: Seasonal UV radiation and global Covid-19 trends
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