CIESIN Reproduced, with permission, from: Tolba, M. K., O. A. El-Kholy, E. El-Hinnawi, M. W. Holdgate, D. F. McMichael, and R. E. Munn, eds. 1992. Ozone depletion. Chapter 2 in The world environment 1972-1992. New York: Chapman and Hall.

Advances in the understanding of stratospheric ozone since mid-l990

Antarctic ozone losses continue:

Strong Antarctic ozone holes have continued to occur, and in four of the past five years have been deep and extensive in area. This contrasts to the situation in the mid-1980s. when the depth and area of the ozone hole exhibited a quasi-biennial modulation. Large increases in surface ultraviolet radiation have been observed in Antarctica during periods of low ozone. While no extensive ozone losses have occurred in the Arctic comparable to those observed in the Antarctic, localized Arctic ozone losses have been observed in winter concurrent with observations of elevated levels of reactive chlorine.

Larger global ozone decreases observed:

Ground-based and satellite observations continue to show decreases of total-column ozone in winter in the Northern Hemisphere. For the first time. there is evidence of significant decreases in spring and summer in both the northern and southern hemispheres at middle and high latitudes (about 3.5% at 45deg.N in summer for the period 1979-1991) as well as in the southern winter. No trends in ozone have been observed in the tropics. The downward trends were larger during the 1980s than in the 1970s by about 2% loss per decade. The observed ozone decreases have occurred predominantly in the lower stratosphere.

Observed ozone losses due to industrial halocarbons:

Recent laboratory research and an extended interpretation of field measurements have strengthened the evidence that the Antarctic ozone hole is primarily due to chlorine- and bromine-containing chemicals. In addition, the weight of evidence suggests that the observed middle- and high-latitude ozone losses are largely due to chlorine and bromine. Therefore, as the atmospheric abundances of chlorine and bromine increase in the future, significant additional losses of ozone are expected at middle latitudes and in the Arctic.

Future levels of ozone depletion:

Even if the control measures of the amended Montreal Protocol (London, 1990) were to be implemented by all nations, the current abundance of stratospheric chlorine (3.3-3.5 parts per billion volume (ppbv)) is estimated to increase during the next several years, reaching a peak of about 4.1 ppbv around the turn of the century, Since the middle latitude ozone losses are apparently due in large part to chlorine and bromine, the increased levels of chlorine and bromine that are estimated by the year 2000 are expected to result in additional ozone losses during the 1990s comparable to those already observed for the 1980s. There is also the possibility of incurring wide spread losses in the Arctic. Reducing these expected and possible ozone losses requires further limitations on the emissions of chlorine- and bromine-containing compounds.