HIGH ALTITUDE POLAR STRATOSPHERIC CLOUDS LIT FROM BELOW NEAR SWEDEN, 2001-10-16 (photo)

This undated photo shows polar stratospheric clouds lit from below near Kiruna, in Sweden. Scientists recently discovered that polar stratospheric clouds, long known to play an important role in Antarctic ozone destruction, are occurring with increasing frequency in the Arctic. These high altitude clouds that form only at very low temperatures help destroy ozone and as the atmosphere above the Arctic has been colder than usual in recent years, such clouds have lasted into the spring. As a result, ozone levels have been decreasing. Clouds such as these, common in Antarctica but a rare sight in the Arctic, are "breeding grounds" for ozone-destroying molecules. REUTERS/HO/NASA/Lamont Poole GN/jp