More good news: scientists predict it will continue to shrink, although its full recovery is not expected until the middle of the century
Every September, a seasonal ozone hole in Earthâ€™s protective ozone layer is formed over Antarctica, a phenomenon discovered in the late 1970s. Since then, its size is measured every year by satellites. As chlorofluorocarbons (CFCâ€™s) and other man-made chemicals were blamed for the hole, their use was banned with the Montreal Protocol, signed in 1987 by 197 nations. â€œIt's extremely rewarding, because it was originally just a scientific effort, and then we were able to convince society that it was a problem â€” here's what would happen if we do not deal with it,â€ said chemist Mario Molina, who had an integral role in the discovery of the ozone hole and who was awarded a Nobel Prize for his research in 1995.
Societyâ€™s collective efforts have begun to show results, as this yearâ€™s ozone hole was similar in size to the hole in 1988 and about 1 million miles smaller than in 2016. It reached its annual maximum on Sept. 11, covering an area about two and a half times the size of the United States â€“ 7.6 million square miles in extent - and then declined through the remainder of September and into October. Since 1991, the average size of these ozone holes (at their yearly maximum) has been roughly 10 million square miles, with that of the year 2000 being the largest, having a width of 11.5 million square miles.
Scientists from NASA and NOAA predict the ozone hole will continue to shrink, yet this yearâ€™s improvement had more to do with weather conditions than human intervention. In fact, the reduced ozone hole extents in 2016 and 2017 were due to natural variability (warmer-than-average stratospheric weather conditions) and not a signal of rapid healing. Moreover, they believe that the current ozone hole area is still of considerable size because levels of ozone-depleting substances like chlorine and bromine remain high enough to produce significant ozone loss and its full recovery is not expected until the middle of the century.