I was invited to respond to this comment:
Bit bemused by the ozone hole story. 2015 was the fourth largest ozone hole since the satellite record began. The peak size is generally reached in October as the sunlight and cold reach their maximum.
Can somebody explain on what basis this claim has been made?
The NYT article links to Solomon et al. (2016):AbstractYour reference NASA’s Earth Observatory website reads:
Industrial chlorofluorocarbons that cause ozone depletion have been phased out under the Montreal Protocol. A chemically-driven increase in polar ozone (or “healing”) is expected in response to this historic agreement. Observations and model calculations taken together indicate that the onset of healing of Antarctic ozone loss has now emerged in September. Fingerprints of September healing since 2000 are identified through (i) increases in ozone column amounts, (ii) changes in the vertical profile of ozone concentration, and (iii) decreases in the areal extent of the ozone hole. Along with chemistry, dynamical and temperature changes contribute to the healing, but could represent feedbacks to chemistry. Volcanic eruptions episodically interfere with healing, particularly during 2015 (when a record October ozone hole occurred following the Calbuco eruption).This series of images shows the size and shape of the ozone hole each year from 1979 through 2015 (no data are available for 1995).
As the images show, the word hole isn’t literal; no place is empty of ozone. Scientists use the word hole as a metaphor for the area in which ozone concentrations drop below the historical threshold of 220 Dobson Units.
The series begins in 1979. The maximum depth of the hole that year was 194 Dobson Units (DU)—not far below the historical low. For several years, the minimum concentrations stayed in the 190s, but beginning in 1983, the minimums got deeper rapidly: 173 DU in 1982, 154 in 1983, 124 in 1985. In 1991, a new threshold was passed; ozone concentration fell below 100 DU for the first time. Since then, concentrations below 100 have been common. The deepest ozone hole occurred in 1994, when concentrations fell to just 73 DU on September 30.
Records in depth and size haven’t occurred during the same years (the largest ozone hole occurred in 2006), but the long-term trend in both characteristics is consistent: from 1980 through the early 1990s, the hole rapidly grew in size and depth. Since the mid-1990s, area and depth have roughly stabilized (see the Ozone Hole Watch website for annual averages). Year-to-year variations in area and depth are caused by variations in stratospheric temperature and circulation. Colder conditions result in a larger area and lower ozone values in the center of the hole.
Scientists estimate that about 80 percent of the chlorine (and bromine, which has a similar ozone-depleting effect) in the stratosphere over Antarctica today is from human, not natural, sources. Models suggest that the concentration of chlorine and other ozone-depleting substances in the stratosphere will not return to pre-1980 levels until the middle decades of this century. These same models predict that the Antarctic ozone layer will recover around 2040. On the other hand, because of the impact of greenhouse gas warming, the ozone layer over the tropics and mid-southern latitudes may not recover for more than a century, and perhaps not ever.
It Just Goes Downhill from ThereWitness:
The basis of the claim is crappy models and a willful obliviousness to the simple fact that the Sun’s ultraviolet output naturally varies so the ozone layer naturally varies. “Over Washington, D.C., ozone varies annually by 25 percent, some 80 times greater than the stated anthropogenic decline.” ~Sallie Baliunas
“…ozone is produced by ultraviolet radiation: If there were no solar UV, there would be no ozone. Since solar UV rises and falls with the 11-year cycle of sunspots, ozone concentration should do likewise. Indeed it does.” ~Sallie Baliunas
Yup, atmospheric scientists don't know nuffin'. I wish I were making this up but I'm not. The first quote comes from this 1995 House Committee hearing, and the second from a whitepaper published by the George C. Marshall Institute in 1994.
Here's my response to Wagathon's first quote, citing the same House hearing testimony:
And there's MOAR, this time from Dr. Daniel Albritton, then of NOAA and co-chair of the UN Ozone Science Assessment Panel:
The second chart shows how the ozone levels have changed over the past 30 years of observations from the ground-based network. The top box gives the raw data that these instruments take and in that you can see the very clear, reproducible, year-by-year annual cycle of ozone simply because, like much of the planet, ozone depends in part on solar activity. The lower panel shows the data after this well-known annual cycle and other variations of natural causes like solar activity and dynamics have been taken out.Amusingly, another Denizen took exception to my dated reference: