2018 · Geophysical Research Letters
Decline in Antarctic ozone depletion and lower stratospheric chlorine from Aura MLS
Strahan and Douglass
What was measured. Aura MLS ozone and inorganic chlorine inside the Antarctic vortex. The paper opens by stating that unambiguous observational proof of a Montreal Protocol effect on Antarctic ozone was still missing more than 20 years after emissions of the controlled gases had peaked.
What it does to the budget. Their own chlorine estimate in the lower stratosphere did fall. The hole did not follow it. They write that year-to-year ozone loss is largely temperature, not chlorine, and that before this analysis there were no inorganic-chlorine observations in the Antarctic lower stratosphere to check the decrease. NASA’s account of the same work: declining chlorine had not yet caused a recovery of the hole; temperature and winds still drive the annual change; chlorine is not expected to control the area until after the mid-2030s. A 20 percent drop in mid-winter chemical loss from 2005 to 2016 can match a model and still leave the September hole size as weather.
The one change they quantified
percent
NASA’s account of this paper: ozone depletion in the winter months fell 20 percent from 2005 to 2016, from MLS ozone. They say that matches the chlorine decline in their model. They also say the hole’s size after mid-September is temperature, which varies year to year. The annual MLS points were not published as a table, so this is the percent they stated, not a redrawn time series.