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Myth: No Link Exists Between Ozone Depletion and Higher UV Levels

Seasonal changes in the UV index

Source: World Meteorological Organization, Scientific Assessment of Ozone Depletion: 2002, WMO Global Ozone Research and Monitoring Project - Report No. 47, Geneva, 2002.

The primary concern related to ozone depletion is the expectation that as the ozone layer deteriorates, higher levels of UVB will reach the ground. Studies done in Antarctica show a clear connection between reduced ozone levels and higher levels of UVB. During the annual ozone hole, UV intensitities more than doubled compared to what would normally be found given the angle of the sun in the sky. A study in Toronto demonstrated the relationship between days of lower ozone and higher UV levels, and other researchers also showed this connection over Germany, Iceland, and Greece. Finally, laboratory experiments confirm that ozone absorbs UVB.

The connection between ozone levels and UV levels is also demonstrated by measurements of incident UV at different parts of the Earth's atmosphere. The sun's rays contain a wide variety of wavelengths. Some of this energy is visible light (400-700 nm), but a wide variety of the electromagnetic spectrum is represented, including various UV bands: UVA (320-400 nm), UVB (290-320 nm), and UVC (shorter than 280 nm). Measurements taken above the ozone layer show that none of the bands have been strongly absorbed. However, lower in the ozone layer, it becomes clear that the ozone molecules are strongly absorbing the UVB and UVC bands. UVC is so completely absorbed by normal oxygen that only nearly complete destruction of the ozone layer will increase its levels on the ground. However, UVB is only absorbed by ozone. For each 1% drop in ozone levels (i.e. 1% increase in ozone depletion), scientists estimate about 1% more UVB will reach the Earth's surface.

The two graphics presented above portray levels of ultraviolet radiation. The first graphic, Changes in Surface Ultraviolet Radiation, shows average percent trends of sunburning surface ultraviolet radiation per decade over various latitudes. A red line represents sunburning radiation. The uncertainty range of these data is shown with yellow shading around the line. The radiation trend is higher at the 60 degree North and South latitudes, and decreases toward the mid-latitudes. The uncertainty ranges from approximately +/- 2 percent to +/- 6 percent. The second graphic, Seasonal Changes in the UV Index, shows levels of sunburning ultraviolet radiation in Palmer, Antarctica (with a red line); San Diego, California (with a green line); and Barrow Alaska (with a blue line) in Winter, Spring, Summer, and Fall. The UV index is a measure of maximum levels of sunburning ultraviolet radiation at a given location on a given day. For all four seasons, the UV index is higher in San Diego than in Barrow. The UV index is higher in San Diego than in Palmer during the Winter, Summer, and Fall. However, in the Spring, the UV index for Palmer sometimes exceeds San Diego 's index values, thus indicating higher levels of ultraviolet radiation reaching the Earth's surface in Palmer. A red dotted line shows that the normal UV index in Palmer was formerly lower than San Diego index values, even during the Spring, before the occurrence of the ozone hole.

J. B. Kerr and C. T. McElroy, "Evidence for Large Upward Trends of Ultraviolet-B Radiation Linked to Ozone Depletion", Science,262, 1032, 1993.

Seckmeyer, G., B. Mayer, R. Erb, and G. Bernhard, "UV-B in Germany higher in 1993 than in 1992", Geophys. Res. Lett., 21, 577-580, 1994.

Zerefos, C. S., A. F. Bais, C. Meleti, and I. C. Ziomas, "A note on the recent increase of solar UV-B radiation over northern middle latitudes", Geophys. Res. Lett., 22, 1245-1247, 1995.

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