SOON AND BRIGGS: Global-warming fanatics take note – Sunspots do impact climate

Leif Svalgaard says: September 13, 2012 at 1:08 am
Science is always imbued with healthy skepticism. The trick is to avoid being paralyzed by said skepticism.
Well is seems that in the cases of CFCs and CO2, there were no problems in performing that trick. Mitigation efforts appear to have begun before the causes of the Antarctic ozone hole and Global Warming were well established.

Leif Svalgaard says: September 11, 2012 at 10:57 pm
The timing of the beginning of the long, slow recovery suggests to me that the ban on some man-made halocarbon refrigerants has been working.
Do you have any sense of what the ozone hole might recover to, e.g. what the natural ozone hole size and ozone content might be?

Further background on early ozone measurements:

“Researcher Joseph Farman had been collecting atmospheric data at Halley Bay, Antarctica since 1957. Every year he sent a team of research assistants to measure ozone levels and concentrations of trace gases like CFCs. In 1982, his ozone reading showed a dramatic dip — around 40%. Rather than being alarmed, he was skeptical of the data and thought it must be an instrument malfunction. The machine was notoriously difficult to keep working in the severe Antarctic cold, and this particular instrument was old. Besides, he reasoned, NASA scientists had satellites collecting atmospheric data from all over the world, and they hadn’t reported any anomalies. Farman’s instrument was ground-based and only had one data point — the part of the atmosphere directly above it. Surely NASA’s thousands of data points would have revealed a drop in ozone if there had been one. Farman ordered a new instrument for next year’s measurement.
But the following year, Farman still found a drastic decline. He dug up his old data and found that the decline had really started back in 1977. Now Farman suspected that something odd was happening strictly over Halley Bay, leaving other areas unaffected. So the next year, his team took measurements from a location 1,000 miles northwest of Halley Bay. Even there, a large decline in ozone occurred. The mounting evidence was undeniable. Farman decided it was time to publish his data.
Why hadn’t NASA’s satellite caught this plunge in ozone levels? Much to their chagrin, NASA scientists realized that they did have data indicating ozone loss but had overlooked it. Since their satellite recorded data 24 hours a day, it supplied scientists with information much faster than they could analyze it. To deal with this deluge, a data processing program had been set up to filter out all measurements below or above cut-off values that were considered to be impossible for actual ozone measurements. This program was based on the assumption that these “impossible” measurements were due to instrument malfunctions. The two groups of scientists (Farman’s group and the NASA group) looked at the same data, but interpreted them differently because of their data analysis techniques. Farman’s group concluded that the data reflected real changes in ozone, while the NASA group had concluded that the data reflected an instrument problem.
Farman’s evidence showed NASA’s group the problem with their data analysis procedure. When NASA scientists reanalyzed their Antarctic measurements, they discovered a gigantic hole in the ozone layer — a region of depleted ozone the size of the United States! Our protective shield from solar radiation had already been damaged even more than scientists had thought possible. The ozone depletion in Antarctica was real, but why was it so much larger than any of the models had predicted? http://undsci.berkeley.edu/article/0_0_0/ozone_depletion_09

Leif Svalgaard says: September 13, 2012 at 9:57 pm
Signe’s paper has lots of good background references too. Worth a look.
Yes, they seem to indicate that there is still a tremendous amount of uncertainty in this area, e.g.:

“Understanding how chemical processes, atmospheric dynamics, temperatures, solar activity and volcanic eruptions affect ozone in the long and short term, and incorporating these factors into models, helps bring model estimates into agreement with observed data. However, many of the effects of these factors are not fully understood, which limits our ability to attribute ozone changes to particular factors. Effects of some of the most important factors and their interactions, together with the limitations in our understanding, are outlined below.”
“Atmospheric dynamics, especially transport of ozone-rich air poleward and strong polar vortices, have direct influences on ozone levels in the short term38–41. Climate change could have long-term effects on atmospheric dynamics throughout the atmosphere. Neither dynamical processes nor dynamical effects on ozone levels are fully understood. For example, recent dynamical activity could be due to natural variability, climate change, or radiative feedbacks resulting from changing concentrations of ozone. Increases in tropopause heights are associated with lower ozone amounts42–44, whereas changes in both the Arctic and North Atlantic oscillations since the early 1990s are associated with higher levels of ozone16,45,46. Climate change may affect dynamical processes by increasing the strength of polar vortices, thereby enhancing polar depletion of ozone47–49, or it could lead to increases in the magnitude of planetary waves causing slightly higher ozone levels50.”
“Major volcanic eruptions inject sulphur into the stratosphere, forming sulphate aerosols that react to destroy ozone60–63. Major eruptions of El Chicho´n in 1982 and Mt Pinatubo in 1991 both occurred during solar maxima, yet had their own large effects on ozone for several years following the events64. Despite the spread of Mt Pinatubo aerosols in the stratosphere of both hemispheres, the eruption resulted in a sharp decline in Northern Hemisphere ozone levels60–62,65,66 but not in Southern Hemisphere levels11.”
“Long-term trends are not expected from solar or volcanic activity but variability in ozone as a result of each complicates recovery detection. Ozone data from the very late 1990s and early 2000s coincide with a period of low volcanic activity favouring higher abundances of ozone. Should another major eruption occur in the next few years, ozone levels are likely to be lower, and, depending on the magnitude of the eruption, they could be similar to those observed in the 1990s.”
Complicating the interpretation of recent ozone data are the effects of natural variability, particularly temperature and dynamical influences as well as solar activity. The most striking data illustrating the effects of temperature on the ozone layer are observations from the northern high latitudes, particularly north of 458N (Fig. 6). Examination of the latitudinal, seasonal and altitudinal signatures of recovery shows that there is coarse agreement between the models and measurements, except in the north, where the data imply much faster recovery than is indicated by the models. The time series illustrate that the trends are strongly affected by the low ozone levels occurring in the mid- to late-1990s, the timeframe in which we begin
to look for signs of recovery. During this time not only was EESC peaking, but the Arctic stratosphere was extremely cold and ozone levels were anomalously low78. Most of the subsequent years have been warm (with a notable exception of the winter of 2004/05), and correspond to an apparent change in the ozone trend51. These unusually low ozone years in the mid- to late-1990s affect the derived trends before 1996, but also after 1996 because the record for the most recent eight years starts from an unusually depleted level. Thus, the representation of the latest increases in ozone north of 408N as evidence of a long-term upward trend and recovery due to declining levels of halogens might be misleading. A change to colder conditions in the Arctic stratosphere would probably lead to reversed trends, at least in the short term. Whereas the effects of these cold winters are well studied for the Arctic, data shown in Fig. 6 suggest that the very low ozone values extend to mid-latitudes as well. The short data record combined with the impact of unusually low ozone levels in the mid- to late-1990s make it difficult to estimate the magnitude of the long-term rates of change in ozone.”
“The solar cycle strongly influences the amount of ozone and complicates the interpretation of data. Figure 1b shows that all three models that include the 11-year solar cycle estimate an increase in ozone for the past eight years. This is a short-term change, not recovery. The magnitude of the effect of the solar cycle differs from model to model, and may be larger than is indicated by the data. Efforts to derive the size of the influence of the solar cycle from past
column ozone time series are complicated by the fact that the prior two solar maxima nearly coincided with the last two major volcanic eruptions. These eruptions offset the increase in ozone expected from increases in solar ultraviolet output. Consequently, some of the increase of total column ozone during the past eight years may be due to the recent solar cycle maximum, but the magnitude of this influence is somewhat uncertain. The data collected over the next few years will be important for separating the influence of the solar cycle from the long-term recovery of the ozone layer.”
“Although many factors affect ozone concentrations and it is difficult to be confident about trend results derived from ten years of data, many of the changes observed in the recent ozone data are qualitatively consistent with what would be expected on the basis of a
reduction in the concentrations of ozone-depleting substances in the atmosphere. Over the past ten years, total column ozone values for most of the world have levelled off or show a slight increase. No area shows significant depletion of total ozone, marking the first ten-year period since 1980 (omitting the perturbation following the eruption of Mt Pinatubo) in which ozone has not declined. The observed levelling off of ozone is generally consistent with declines in ozone depleting substances due to international agreements controlling their production. However, the large increases in column ozone observed in the mid- to high-northern latitudes are probably due to the higher temperatures in the Arctic polar vortex as well as to solar influence and the recent lack of volcanic activity. In contrast, the winter of 2004/05 was extremely cold in the Arctic stratosphere, allowing for severe ozone depletion before the polar vortex broke up. The 11-year solar cycle recently peaked and its influence on ozone is uncertain, but solar variability appears to have contributed to some of the observed leveling off and increases in ozone over the past eight years.”
“The model-calculated abundances of column ozone are normalized to 1980 levels to remove differences between measured and modelled column ozone as high as 30 Dobson units (total column ozone is measured in Dobson units (DU), the number of ozone molecules in a column of atmosphere; at standard pressure and temperature, 330DU would be 3.3mm thick). Because of the normalization to 1980, when solar activity was at a peak, this representation overestimates the difference in depletion between measurements and models for 608 N–608 S. However, this bias is removed when trends are derived and presented below.”
“Standard statistical techniques are used to remove from the ozone data the effects of variability due to solar inputs and dynamical factors8,16. One problem with this approach is that different environmental parameters can behave in a similar manner, making it difficult to separate influences through analytical techniques. Another problem is that, in some cases, ozone levels, stratospheric circulation, and temperatures interact and limit attempts to attribute changes through a purely analytical approach. The scientific difficulty concerns interpretation of the recent data—as a sign of ozone recovery, as simple variability, or as a combination of several parameters that affect ozone. Despite the existing uncertainties, latitudinal, seasonal and altitudinal signatures of recovery stand out as robust in the model projections because they spatially and temporally link current ozone increases to patterns of post-1980 ozone depletion.

It is thus confusing, given the tremendous uncertainty, that the first sentence of Signe’s paper begins with;

“Evidence of mid-latitude ozone depletion and proof that the Antarctic ozone hole was caused by humans”.

It appears that the only evidence presented to support this assertion is;

In the early 1970s, Molina and Rowland5 first theorized that chlorine compounds—manufactured as refrigerants and aerosol propellants—could destroy ozone in the Earth’s stratosphere, a theory confirmed in 1985 by a measured ozone loss over Antarctica 6,7. Stratospheric ozone levels significantly declined until the mid-1990s8 with the largest rates of depletion near the poles and no noticeable depletion near the Equator.

The three references cited within are;

6 Farman, J., Gardiner, B. & Shanklin, J. Large losses of total ozone in Antarctica
reveal seasonal ClOx/NOx interaction. Nature 315, 207–-210 (1985).
7. Solomon, S., Garcia, R. R., Rowland, F. S. & Wuebbles, D. J. On the depletion of
Antarctic ozone. Nature 321, 755–-758 (1986).
8. Staehelin, J., Harris, N. R. P., Appenzeller, C. & Eberhard, J. Ozone trends: A
review. Rev. Geophys. 39, 231–-290 (2001).

Here is the abstract for Farman, J., Gardiner, B. & Shanklin, J. Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction;

Recent attempts1,2 to consolidate assessments of the effect of human activities on stratospheric ozone (O3) using one-dimensional models for 30° N have suggested that perturbations of total O3 will remain small for at least the next decade. Results from such models are often accepted by default as global estimates3. The inadequacy of this approach is here made evident by observations that the spring values of total O3 in Antarctica have now fallen considerably. The circulation in the lower stratosphere is apparently unchanged, and possible chemical causes must be considered. We suggest that the very low temperatures which prevail from midwinter until several weeks after the spring equinox make the Antarctic stratosphere uniquely sensitive to growth of inorganic chlorine, ClX, primarily by the effect of this growth on the NO2/NO ratio. This, with the height distribution of UV irradiation peculiar to the polar stratosphere, could account for the O3 losses observed. http://adsabs.harvard.edu/abs/1985Natur.315..207F

Here is the abstract for Solomon, S., Garcia, R. R., Rowland, F. S. & Wuebbles, D. J. On the depletion of Antarctic ozone;

Recent observations by Farman et al. 1 reveal remarkable depletions in the total atmospheric ozone content in Antarctica. The observed total ozone decreased smoothly during the period from about 1975 to the present, but only in the spring season. The observed ozone content at Halley Bay was ~30% lower in the Antarctic spring seasons (October) of 1980–84 than in the springs of 1957–73. No such obvious perturbation is observable in other seasons, or at other than the very highest latitudes in the Southern Hemisphere, and the magnitude of the observed change there far exceeds climatological variability2. We present here balloonsonde ozone data3,4 which show that these ozone changes are largely confined to the region from about 10 to 20 km, during the period August to October. We show that homogeneous (gas phase) chemistry as presently understood cannot explain these observed depletions. On the other hand, a unique feature of the Antarctic lower stratosphere is its high frequency of polar stratospheric clouds5, providing a reaction site for heterogeneous reactions. A heterogeneous reaction between HCl and ClONO2 is explored as a possible mechanism to explain the ozone observations. This process produces changes in ozone that are consistent with the observations, and its implications for the behaviour of HNO3 and NO2 in the Antarctic stratosphere are consistent with observations of those species there, providing an important check on the proposed mechanism. Similar ozone changes are obtained with another possible heterogeneous reaction, H2O + ClONO2. http://www.nature.com/nature/journal/v321/n6072/abs/321755a0.html

Here is the abstract for Staehelin, J., Harris, N. R. P., Appenzeller, C. & Eberhard, J. Ozone trends: A review;

Ozone plays a very important role in our atmosphere because it protects any living organisms at the Earth’s surface against the harmful solar UVB and UVC radiation. In the stratosphere, ozone plays a critical role in the energy budget because it absorbs both solar UV and terrestrial IR radiation. Further, ozone in the tropopause acts as a strong greenhouse gas, and increasing ozone trends at these altitudes contribute to climate change. This review contains a short description of the various techniques that provided atmospheric ozone measurements valuable for long-term trend analysis. The anthropogenic emissions of substances that deplete ozone (chlorine- and bromine-containing volatile gases) have increased from the 1950s until the second half of the 1980s. The most severe consequence of the anthropogenic release of ozone-depleting substances is the “Antarctic ozone hole.” Long-term observations indicate that stratospheric ozone depletion in the southern winter-spring season over Antarctica started in the late 1970s, leading to a strong decrease in October total ozone means. Present values are only approximately half of those observed prior to 1970. In the Arctic, large ozone depletion was observed in winter and spring in some recent years. Satellite and ground-based measurements show no significant trends in the tropics but significant long-term decreasing trends in the northern and southern midlatitudes (of the order of 2–4% per decade in the period from 1970 to 1996 and an acceleration in trends in the 1980s). Ozone at northern midlatitudes decreased by −7.4±2% per decade at 40 km above mean sea level, while ozone loss was small at 30 km. Large trends were found in the lower stratosphere, −5.1±1.8% at 20 km and −7.3±4.6% at 15 km, where the bulk of the ozone resides. The possibility of a reduction in the observed trends has been discussed recently, but it is very hard to distinguish this from the natural variability. As a consequence of the Montreal Protocol process, the emissions of ozone-depleting substances have decreased since the late 1980s. Chlorine is no longer increasing in the stratosphere, although the total bromine amount is still increasing. Considering anthropogenic emissions of substances that deplete ozone, the turnaround in stratospheric ozone trends is expected to take place in the coming years. However, anthropogenic climate change could have a large influence on the future evolution of the Earth’s ozone shield. http://www.agu.org/pubs/crossref/2001/1999RG000059.shtml

Is the “proof that the Antarctic ozone hole was caused by humans” asserted within Signe’s paper based upon Staehelin’s assertion that “The most severe consequence of the anthropogenic release of ozone-depleting substances is the ‘Antarctic ozone hole.'”?