The ozone layer over the Arctic has thinned dramatically this winter, say European and American scientists working on the world’s biggest ozone-monitoring experiment. More than 60 percent of the ozone layer has been lost at certain altitudes over the North Pole, a deterioration from 1997, which had previously been the worst year for the ozone layer. The thin area could be blown south by high-altitude winds and appear over populated areas of Europe and North America. Depletion of the ozone layer, which is the key filter for damaging ultraviolet-B radiation, could lead to greater incidence of skin cancer, eye cataracts, and immune system problems in humans, as well as health problems in other species.