Rising levels of "greenhouse gases" in the atmosphere will lead to further depletion of earth's protection ozone layer and could produce an Arctic "ozone hole" equivalent to the one already appearing around the south pole, acccording to NASA analysis. That could be bad news for those who thought "we had the ozone problem solved because of treaty limits on CFC's and othe ozone depleting substances," said Drew T. Shindell of Columbia University and NASA's Goddard Institute for Space Studies in New York.