Background
I was invited to respond to this comment:
climatereason
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.
http://earthobservatory.nasa.gov/Features/WorldOfChange/ozone.php
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 There
Witness: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:
More for Wagathon:
STATEMENT OF DR. ROBERT T. WATSON, ASSOCIATE DIRECTOR OF ENVIRONMENT, OFFICE OF SCIENCE AND TECHNOLOGY POLICY, EXECUTIVE OFFICE OF THE PRESIDENT, WASHINGTON, DC
[…]
Since the late 1970s, ground-based, balloon and satellite data have documented significant decreases in column content of ozone over Antarctica, about 60 percent, as shown in one of my figures in my testimony, and drastic changes in the vertical distribution, close to 100 percent loss of ozone at certain altitudes.
Since the late 1970s, ground-based, balloon and satellite data have documented significant decreases in column content of ozone over Antarctica, about 60 percent, as shown in one of my figures in my testimony, and drastic changes in the vertical distribution, close to 100 percent loss of ozone at certain altitudes.
The Antarctic ozone holes in 1990, 1992, 1993, and 1994, were the most severe on record.
As we speak today, and as expected, satellite, balloon, and ground-based data show that the Antarctic ozone hole is once again developing in the fashion similar to the last few years.
There is absolutely no doubt that the springtime Antarctic ozone hole is due to the increasing concentrations of anthropogenic chlorine and bromine. This conclusion is based on combining extensive ground, aircraft, balloon and satellite data with laboratory data and theoretical modeling.
[…]
With respect to global ozone, the observational data, as I’ve shown in figure 4 of my testimony, provides conclusive evidence that ozone depletion is occurring at all latitudes, except the tropics, and in all seasons.
Analysis of extensive ground-based Dobson and TOMS data through 1994 has shown that column ozone has decreased by 5 to 6 percent in summer in the northern hemisphere, 9 to 11 percent in winter/spring in the northern hemisphere, 8 to 9 percent in southern mid-latitudes on a year-round basis.
Figure 5 in my testimony also shows the seasonal and latitudinal trends, illustrating the very significant trends at middle and high latitudes.
In each case, the natural periodic and episodic fluctuations are taken into account — ***SOLAR CYCLE***, season and volcanic activities.
The weight of scientific evidence strongly suggests that the observed mid-latitude ozone trends are due in large part to anthropogenic chlorine and bromine.
Yup, looks like “willful obliviousness to the simple fact that the Sun’s ultraviolet output naturally varies” to me.
Not. Trot out more claptrap about what atmospheric scientists allegedly don’t understand again, and you and I can have a nice little chat about whether or not your ignorance is willful or not, hey?
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:
brgates, 1995? In 2015 they were still trying to figure out how the BD circulation dynamics caused twice as much NH mid-latitude O3 than in the SH.
brgates, my comment was on your choice of an outdated source.
I don’t see this as convincing evidence of a strong recovery of Antarctic ozone.
I don’t find this impressive either. So news of the resurrection of the polar ozone might be a bit premature, IMHO
Ok, What do the Data Really Say?
... because that doesn't look like solar cycles to me:
So we've got Antarctic ozone data from here, and CFC mixing ratios from here.
Regress them, and we get these pretty pictures:
So yeah, when I take the residual of what total CFC concentration would predict for ozone and regress it against against solar activity, we do see a relationship. Which isn't surprising or controversial. Nor is it surprising to me that CFCs are the better predictor of the long-term trend.
That's really all I should have to say, but some people like manufacturing controversy.
