Wait—the #Ozone Layer Is Still Declining? - Scientific American
Ball and a team of researchers from institutions around the world wanted to more accurately measure trends in the ozone layer. For their study, they synthesized and then analyzed multiple satellite data sets of atmospheric ozone. The data cover the tropics and mid-latitudes, from 1985 through 2016. The team found ozone in the upper stratosphere has indeed rebounded since 1998. “It’s clear it’s going back up,” Ball says. “This is exactly where we’d expect to see the Montreal Protocol working its best.” They also discovered ozone in the troposphere—which comes in large part from air pollution—rose from 2004 through 2016.
They observed, however, no significant upward or downward trends for the middle stratosphere, or for the total ozone column—the sum of the troposphere and stratosphere—since 1998. Starting in 1985 “you can see [the total ozone column] is going down,” Ball says. “After 1998 we see ozone stop depleting, initially see a slight rise and then it seems to stall.” But the rise was statistically nonsignificant, Ball notes. “What this says is, great, since 1998 ozone hasn’t been depleting any further.” But it also does not appear to be rebounding.
What is the culprit? Ball’s team found the ozone in the lower stratosphere has slowly, continuously dropped since 1998. “We see a small but persistent and continuous decline—not as fast as before 1998 but a continued [trend] down,” he says. “This is surprising, because we would have expected to also see this [region’s ozone] stop decreasing.” The finding is important because the lower stratosphere contains the largest fraction of the ozone layer.