Conclusions

         1. In 2002-2004, average TCO over Canada was higher than over all other chosen locations, including same latitudes in the Southern hemisphere. During the local summer, TCO over Canada varied from 270 to 330 DU. This suggests that prolonged outdoor activity in Canada is safer than in other chosen locations.

         2. TCO over the same location as Canada, but in the Southern hemisphere was lower than in Canada. This is probably because of the higher ozone depletion in the Southern hemisphere, which is clearly seen during local spring (September-November).

         3. TCO over Australia varied from 240 to 270 DU during the local summer. This is 10 DU lower than TCO over similar latitude/longitude range in the Northern hemisphere, but is exactly the same as TCO over Central Africa (from 10°S to 10°N).

         4. It seems that TCO over Australia is not lower than over Central Africa and, therefore, is not the lowest in the world. Therefore, highest rate of skin cancer (1:30) in Australia cannot be explained only by the decreased ozone levels. Other possible factors could be: a) large number of people with higher skin sensitivity (i.e. settlers from Ireland); b) excess of beaches and extended periods of hot and sunny weather; c) not very reliable cancer statistics in Central Africa; d) lower life expectancy in Central Africa (where the number of people older than 70 is much smaller than in Australia).

         5. While TCO over locations in the Northern hemisphere did not show any significant changes during 2002-2004, TCO in the Southern hemisphere was lower in 2004 than in 2002 and 2003. This could be a very alarming sign of continuing ozone depletion in the Southern hemisphere.

FUTURE WORK