"'The search for signs of recovery of the ozone layer' by Elizabeth Westhead and Signe Andersen.
Sorting out cause and effect is difficult, but a group of NASA and university researchers may have made some headway. Their new study, entitled 'Attribution of recovery in lower-stratospheric ozone,' was just accepted for publication in the Journal of Geophysical Research. It concludes that about half of the recent trend is due to CFC reductions.
Lead author Eun-Su Yang of the Georgia Institute of Technology explains: 'We measured ozone concentrations at different altitudes using satellites, balloons and instruments on the ground. Then we compared our measurements with computer predictions of ozone recovery, [calculated from real, measured reductions in CFCs].' Their calculations took into account the known behavior of the sunspot cycle (which peaked in 2001), seasonal changes in the ozone layer, and Quasi-Biennial Oscillations, a type of stratospheric wind pattern known to affect ozone.
What they found is both good news and a puzzle.
The good news: In the upper stratosphere (above roughly 18 km), ozone recovery can be explained almost entirely by CFC reductions. 'Up there, the Montreal Protocol seems to be working,' says co-author Mike Newchurch of the Global Hydrology and Climate Center in Huntsville, Alabama.
The puzzle: In the lower stratosphere (between 10 and 18 km) ozone has recovered even better than changes in CFCs alone would predict. Something else must be affecting the trend at these lower altitudes.
The 'something else' could be atmospheric wind patterns. 'Winds carry ozone from the equator where it is made to higher latitudes where it is destroyed. Changing wind patterns affect the balance of ozone and could be boosting the recovery below 18 km,' says Newchurch. This explanation seems to offer the best fit to the computer model of Yang et al. The jury is sti"