Long Term Changes in UVEry

While the effects of ozone depletion on UVEry have been large in the Antarctic region (Kerr et al., 2003), the effects have been relatively small in populated areas at lower latitudes. At mid-southern latitudes, summertime ozone, and therefore UVEry, is influenced by the export of ozone-poor air from the Antarctic ozone hole (Roy et al., 1990). Long term measurements at Lauder, New Zealand (45°S, 170°E, altitude 370 m) provide some of the strongest evidence outside the Antarctic region for increases in UVEry attributable to ozone depletion. Results are shown in Fig. 2.1. The increases in peak UVEry due to ozone depletion were relatively modest, ~10% - 15%, with a peak in late 1990s, and a decrease since that time. Other measurement sites, which are generally more polluted, show larger variabilities from sources other than ozone (WMO, 2007). These findings demonstrate that, outside the region affected by the Antarctic ozone hole, changes in UVI due to changes in ozone are rather small and are within the range of variability from other causes. Outside polar regions, ozone levels are expected to return to pre-1980 levels around the middle of the 21st century. Inside polar regions, the recovery is expected to be delayed by a further 10 to 20 years due to an interaction with global warming whereby the expected cooler stratospheric

1 Erythemally weighted UV irradiance. UV radiation weighted by the erythema action spectrum. 22

temperatures will tend to favor the more widespread development of polar stratospheric clouds. Reactions on the surface of these clouds can greatly accelerate ozone depletions, as currently happens each spring in Antarctica (WMO, 2007). The relatively small magnitude of changes in ozone and UV, and the optimistic outlook for the future, are attributable to the success of the Montreal Protocol and its subsequent amendments and adjustments.

Figure 2.1 Upper panel: Mean ozone (Dobson Units, 1 DU = 2.69 x 10 molecule cm 2) at Lauder, New Zealand for the summers of 1978 - 1979 through 2007 - 2008. Lower panel: Corresponding estimates of UV Index. Summer is defined as the period from December through February. The solid lines show the changes in summertime ozone that have occurred since the 1970s and the deduced changes in clear-sky UV expected from these changes in ozone. The symbols (from 1989 - 1990 on) show measured values of ozone and the summertime peak UV Index, both derived from the UV spectroradiometer (McKenzie et al., 2000)

Figure 2.1 Upper panel: Mean ozone (Dobson Units, 1 DU = 2.69 x 10 molecule cm 2) at Lauder, New Zealand for the summers of 1978 - 1979 through 2007 - 2008. Lower panel: Corresponding estimates of UV Index. Summer is defined as the period from December through February. The solid lines show the changes in summertime ozone that have occurred since the 1970s and the deduced changes in clear-sky UV expected from these changes in ozone. The symbols (from 1989 - 1990 on) show measured values of ozone and the summertime peak UV Index, both derived from the UV spectroradiometer (McKenzie et al., 2000)

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