The past few days have been so hot that the midday sun is so hot that it stings. As proof of this, the UV index was also found to be ‘very high’ in most of the country from the 30th of last month to the 3rd of this month. As summer approaches, the sun rises and the weather continues to be clear with no clouds. As such, the UV index rises and falls depending on the season and the weather on that day, but it appears to have continued to increase globally over the past few decades. This is because the ozone layer decreases and the ultraviolet rays that enter the earth become stronger. However, as the ozone layer appears to be recovering recently, opinions are divided as to the future trend of the UV index.
The sun shines a vast spectrum of light on Earth. Among them, light in the short wavelength band of 10 to 400 nm (nanometer, 1 nm is 1 billionth of a meter) is invisible ultraviolet (UV) light. Adequate UV exposure is necessary for vitamin D synthesis, but excessive exposure can cause pigmentation disorders such as freckles or, in severe cases, skin cancer. Among the wavelengths of ultraviolet light, ultraviolet A (UV-A) in the 320 to 400 nm band and ultraviolet B (UV-B) in the 280 to 320 nm band have this effect on the human body. Ultraviolet C (UV-C), which has a shorter wavelength than this, is mostly blocked by the Earth’s atmosphere.
Ultraviolet A mostly reaches the surface regardless of the season. It penetrates deep into the skin and affects dryness, immunosuppression, wrinkles, and darkening of the skin. About 5% of UVB rays reach the surface and become stronger in summer. It affects the skin surface and causes freckles, sunburn, freckles, age spots, erythema, and skin cancer. The blocking effect of sunscreen is expressed as ‘PA+’ and ‘SPF’, respectively.
The Korea Meteorological Administration is measuring the amount of ultraviolet radiation by placing ultraviolet meters in seven places across the country, including Seoul, Pohang, Mokpo, Gangneung, Gosan, and Anmyeon-do. The UV index is predicted by multiplying the observed UV radiation by a weight for a specific wavelength and combining it with cloud, atmospheric condition and altitude data. Usually, when there are a lot of clouds and air pollutants, UV rays in the atmosphere are blocked and the UV index is lowered.
The domestic UV index is calculated as a number from 1 to 11, and the forecast is divided into five stages. The highest stage is the ‘dangerous’ stage, when the UV index is 11 or higher. If you are exposed to the sun, you can burn your skin within a few tens of minutes, so you should stay indoors as much as possible. The ‘very high’ level that appears frequently recently is when the index is greater than or equal to 8 and less than 11. Because skin burns can occur within a few tens of minutes, the Korea Meteorological Administration recommends avoiding going out or staying in the shade between 10 am and 3 pm.
As most countries around the world use this UV index system, the UV index characteristics of each country can also be compared. For example, the maximum UV index in summer in the UK is 6-8, whereas in Australia it is 10-14. Sarah Loughran, a senior researcher at the Australian Bureau of Radiation Protection and Nuclear Safety, explained four reasons for this discrepancy through ‘Dialogue’, an expert contribution website, in December last year.
The first is the latitude difference. The latitude of Australia is 9 degrees and the latitude of the UK is 51 degrees. The lower the latitude, the closer to the equator, the higher the sun’s altitude. The higher the sun’s altitude, the less sunlight it has to pass through the atmosphere, which in turn increases the amount of ultraviolet light reaching the Earth’s surface. “Australia has less UV protection because it has fewer air pollution particles than large cities in the northern hemisphere,” Loughran said.
The last reason is the ozone layer. The ozone layer absorbs UVB rays. When the ozone concentration decreases by 1%, the amount of UVB increases by 2%, which increases the risk of related diseases such as skin cancer by 3-4% and cataract by 0.6%. The ozone layer gets thinner as you go to the South Pole. For this reason, the UV index of countries in the southern hemisphere, including Australia, tends to increase.
The ozone layer not only makes the difference in UV rays between countries, but is also the factor that has had the greatest impact on the rise of the global UV index in recent decades. In 1985, the British Antarctic Survey team confirmed that there was a hole in the ozone layer over Antarctica and published it in the international scientific journal ‘Nature’, revealing the seriousness of ozone layer depletion. In response, 46 countries adopted the ‘Montreal Protocol on Substances that Deplete the Ozone Layer’ in 1987 and started to ban or regulate the use of chlorofluorocarbons, an ozone-depleting substance, but it was not enough to restore the ozone layer immediately. A research team from the National Aeronautics and Space Administration (NASA) announced that the level of ultraviolet B (305 nm) in mid-latitudes increased by about 6% in 2008 compared to 1979 due to the decrease in the ozone layer in 2010.
Only recently have the ozone layer been gradually recovering. As China cracked down on the illegal production of chlorofluorocarbons in China since 2017, the concentration in the atmosphere has significantly decreased. According to the research results published in ‘Nature’ by the National Oceanic and Atmospheric Administration in February this year, the amount of fluorocarbon trichloride in the atmosphere, which increased significantly in the 2010s, started to decrease rapidly after 2017. The research team explained that at the end of 2019, carbon trichloride decreased by 1% per year, suggesting that the ozone layer is on a recovery track.
There is a forecast that the ozone layer will recover and the UV index will decrease in the future, but there are factors that prevent it. “The use of fossil fuels will decrease in the future, and air pollutants will decrease,” said Ruffran, chief researcher. A joint research team at the Japan Center for Ocean Science and Technology and the National Academy of Environmental Sciences predicted that the UV index would rise in the future because the reduction in atmospheric particles and clouds had a greater effect on the UV index than the recovery of the ozone layer as a result of simulations in 2011.
Conversely, as forest fires are increasing due to climate change, there is a possibility that atmospheric particles generated from forest fires may actually block UV rays. “The UV index will also be affected by how the shape of clouds changes due to rapid climate change,” said Ruffran, senior researcher.
This is the ozone layer over Antarctica observed from November 24 to December 4, 2020 by a joint research team of four countries: Chile, Spain, Japan and Germany. The black dotted line is the hole in the ozone layer. The research team said that although the ozone layer is showing signs of recovery, the UV index of Antarctica in December last year was 14.2, close to the record high of 14.8, and there is still a lot of volatility. Provide scientific report