Washington - Scientists say warm upper air this September and October helped shrink the man-made ozone hole near the South Pole slightly.The hole is an area in the atmosphere with low ozone concentrations. It is normally at its biggest this time of year. The US space agency says on average it covered 20.9 million sqaure kilometres this season. That's 6% smaller than the average since 1990.High-altitude ozone shields Earth from ultraviolet radiation.Nasa chief atmospheric scientist Paul A Newman said the main reason for this year's result is local weather. The upper air has been warmer than normal, which led to fewer polar stratospheric clouds. These clouds are where ozone is destroyed by chlorine and bromine, which come from man-made products.