If ozone is depleted over polar regions, even in the Arctic, there is no direct effect on ozone over populated regions of the Earth's surface such as the temperate Northern hemisphere. Most ozone in the stratosphere is generated near to the equator, effectively isolating the northern from the southern hemisphere. This means that the Antarctic Ozone Hole, where half of the stratospheric ozone is temporarily lost for two months of each year, does not affect the Northern hemisphere at all. If ozone were to be lost in the Arctic then ozone poor air would circulate afterwards through the stratosphere and mix with ozone rich air from the tropics, diluting it.
Recent analyses of ozone data have confirmed the general long term trend in the Northern hemisphere: there has been a statistically significant decline in total ozone in all seasons with larger reductions in winter and spring than in summer and autumn.
Starting from the early 1990s, a change in this trend is apparent. The record low values in 1992/93, that followed the eruption of Mt. Pinatubo, still remain the lowest observed but subsequently the total ozone values have remained steady at 4 to 6% lower than those around 1980. The reasons for this apparent break in the long term declining trend are not yet clear but similar depletion has occurred over southern "mid-latitudes". Over the whole region from 60°N to 60°S total ozone is now 3 to 4 % lower than in the 1970s.(1)
This reduction in ozone is calculated to result in a similar sized increase in UVB reaching the Earth's surface. To put the increase into context, it would be equivalent to moving house permanently a few hundred kilometres south (based on the change in strength of sunlight, which does not always reflect a change in temperature).
Examples of the sort of move:
Amsterdam to Luxembourg
Belfast to Cork
Bologna to Roma
Brussels to Strasbourg
Edinburgh to Manchester
Hannover to Mannheim
Oslo to Göteborg
Paris to Genève
(April 2003)
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