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Proceedings of the International Commission on History of Meteorology 1.1 (2004)

11.  Data Collection and the Ozone Hole:

Too much of a good thing?1

Maureen Christie

Department of History & Philosophy of Science
University of Melbourne, Australia

The Problem

It was 1985. An article had just appeared in Nature announcing a large seasonal
disappearance of ozone from the atmosphere over the Antarctic2. The community of
atmospheric scientists was in disarray. Why? What was going on?

Science in the late twentieth century appears to be a large-scale, orderly, and
conservative enterprise. Major surprises were rare, but they did occur from time to time.
Why was this announcement such a surprise?

Everyone was focussed on the ozone layer and possible human influences. There
had been both scientific and public debate for a decade.

1.  Scientists had been strenuously searching for ozone depletion. Their best
current data indicated a possible depletion of 2-3 % — barely detectible. But
this article claimed local depletions of up to 60%.

2. Why did the data come from a single British ground observing station? NASA
had a satellite in orbit, continuously monitoring ozone levels world-wide. The



Data Collection and the Ozone Hole 100

British team leader was a good scientist, with a reputation for careful,
conservative, and scholarly work. But he was not widely known as a leading
atmospheric scientist. Those atmospheric scientists who knew Farman knew
he would not lightly publish such an article; many did not know him.

3. A major new research effort had been put into investigations of stratospheric
circulation and chemistry. Better understandings of chemical mechanism and
atmospheric circulation, along with improvements in computer technology
had been incorporated into the modelling. None of the models had indicated
anything unusual happening in the Antarctic. Stratospheric reaction systems
are largely light-driven. Everyone was expecting daytime in the upper tropical
stratosphere as the likely place for active chemistry.  Polar air in the lower
stratosphere is second only to night-time for absence of ultraviolet light! It
was regarded largely as a chemically inert reservoir.

4. The article shows an anomaly only in the Antarctic, only in the spring months,
and only in years since 1977.  A depletion that is both local and seasonal, and
started quite suddenly in 1976 or 1977 was a surprise.

5. In the context of great scientific interest in stratospheric ozone, why did it take
eight years for the announcement to be published? Four years of data
collection — up to1980 — would have been enough to confirm that there was
a persistent trend rather than just an anomalous season or two. The same four
years could have been used for instrument calibration and re-checking, to rule
out artefactual explanations. Why did the article not appear in 1981?

These issues, then, provide the focus of this article. Several important questions arise:

♦ Why did the publication take so long when everyone was looking so hard?

♦ Why had the announcement not come from the NASA satellite team, which
was better resourced, and had been engaged in more intensive data collection?

♦ Why was the announcement made on the basis of data from a single ground
station? There were over 200 such stations around the world, 17 of them in the
Antarctic.

I will address these questions in reverse order.

Other Ground Stations

A large network of ground stations for worldwide ozone monitoring was set up
for the International Geophysical Year 1957-1958. But the initial enthusiasm waned.
Funding for personnel and instrument maintenance and calibration fell away in many
cases. Some stations were reporting ozone readings on an intermittent and irregular basis.
Some had stopped and restarted at various stages. Some gave up altogether. When ozone
depletion became an issue in the early 1970s, new stations joined the network, and some
dormant programmes were resurrected.



Proc. ICHM 1.1 (2004) 101

Most of the monitoring stations classified as Antarctic are located near or outside
the Antarctic Circle. They did not fall within the area affected by the phenomenon, or at
least did not consistently do so. From one of these stations, the Japanese Syowa station,
there is a conference report from 1984 of anomalously low ozone in the 1983 Austral
spring season3. It was presented at the time as a singular rather than an ongoing
phenomenon.

There are few remaining stations. The French station at Dumont d'Urville was
then in a dormant phase, at least as far as reporting ozone readings is concerned. Soviet
operations at Mirnyy had been hampered from the start with appalling weather
conditions, and they were in the process of relocating most of their Antarctic operations
to a more amenable location at Molodezhnaya. Observations from Mirnyy were both
sparse and questionably erratic. The ozone monitoring instrument at the American base at
the South pole had its own particular problem at the crucial time. That left only the
British station at Halley Bay to make the crucial observations.

The Satellite Observations

The satellite programme collected about 140,000 readings per day, covering the
whole surface of the Earth. Computing technology was primitive by today’s standards.
The readings were analysed for quality control purposes, and archived on magnetic tape
for distribution to scientists interested in working with the data. Local averaging and
graphical presentation were not then within the scope of the software. The ozone maps
that we are now familiar with were still some years away.

There is a nice myth with an appropriate moral, which has been widely circulated
to explain the failure of the satellite team to discover the Antarctic Ozone Hole. One of
several published sources puts it in these terms:

Interestingly, it was discovered that US measuring satellites had not previously
signaled the critical trend because their computers had been programmed
automatically to reject ozone losses of this magnitude as anomalies far beyond the
error range of existing predictive models.4

The moral, of course, is to beware of automatic routines, and to be very careful about
what you do with outliers.

This story is at best a gross over-simplification, and more probably just plain
wrong! Within a year after the publication of the British Antarctic Survey paper, an
article by the NASA scientists appeared in Nature5. It confirms the British data, and
clarifies that the phenomenon covers most of the Antarctic continent, and not just the
Halley Bay area. No hint of an excuse or explanation is given for the late appearance of
their article. But it is clear that computer programs had not ‘rejected’ anomalously low
ozone readings, else they could not have been resurrected for analysis in this article. At
the very least, the satellite data had been properly archived!

An account provided by one of the NASA scientists is published elsewhere6.
Anomalouly low ozone levels were not rejected, but flagged. Early in 1984, the quality



Data Collection and the Ozone Hole 102

control team at NASA had been aware of a cluster of low ozone occurrences in Antarctic
readings from September-October 1983. But they thought they were looking at an
instrument problem, because their data did not match the normal levels being reported
from the American South Pole ground station at the same time. They had only just
become convinced that the anomaly was real and not instrumental when the British paper
appeared.

So why were ground readings from the South pole being reported as normal when
ozone levels clearly were not normal? For a period of several months in 1983, the
wavelengths of the South Pole spectrometer were set to the wrong values. The result was
an apparently steady ozone level of around 300 dobson units. The South Pole data for the
relevant period were later declared ‘erroneous and uncorrectable’. I do not know, and do
not think I am likely to find out why this happened.

But there is a second, and deeper unanswered question. It concerns the years from
1977 to 1982. It is all very well for NASA to investigate when low ozone is continually
flagged in 1983. But what about the previous six years? During those Austral spring
seasons, the majority of ozone measurements in the Antarctic were seldom low enough to
trigger the low ozone flag.  But the ozone levels observed were noticeably lower than the
‘normal’ minimum for that time and place. There is plenty of room for noticeable
anomaly between the 180 unit trigger and the 280 unit lower limit of the usual range of
scatter (see fig. 1).



Proc. ICHM 1.1 (2004) 103

Figure 1: Halley Bay observations compared with satellite "low ozone" flag level.

Again, I do not know the answer. I think it is very mundane. I think nobody
noticed because nobody was looking. All of the scientists involved had other priorities
and preoccupations. The dataset was too large, and in a format too user unfriendly for a
casual overview. It was inaccessible for any analysis that did not take a preconceived
point of view. When you knew what to look for, it was not hard to find. But it was not
possible to “notice” anything unusual. I will return to this in the concluding section.



Data Collection and the Ozone Hole 104

The British Antarctic Survey Analysis

The BAS had maintained the discipline of regular and careful data collection. But
the ozone monitoring project had come to be seen as a routine exercise of low-priority.

A lag had developed in entering the data onto the computers at Cambridge, and
transforming spectrometer readings into actual ozone levels. About five to seven years’
worth of raw data was waiting to be entered and analysed in 1981, including the crucial
years when the ozone hole first appeared. The junior authors discovered the anomalous
springtime data very quickly when they started to work on this backlog. Farman was not
immediately convinced. He was aware of a very unstable and somewhat unpredictable
circulation pattern that prevailed in the Antarctic spring, associated with the break-up of
the winter polar vortex. He felt that ozone levels might be quite erratic at that time of
year. Interestingly, he had previously argued in other publications that autumn levels of
Antarctic ozone were the best guide to global ozone depletion because they were
particularly stable, and less affected by other factors7 than any other location.

Farman was a cautious and conservative scientist. He asked for three main things
before he would be prepared to publish:

♦ results from at least one more spring season to confirm the trend.

♦ recalibration and changeover of spectrometers at Halley Bay, to rule out
instrumental artefacts

♦ a good explanation for why the NASA team had not seen unusual ozone
levels.

In the event, spectrometers were swapped, comprehensively ruling out instrumental
misbehaviour. Attempts to communicate with the NASA scientists failed. And data from
three more seasons not only confirmed the anomaly, but showed it continuing to
intensify. The publication went ahead, both later and stronger than it might have been.

Conclusion

I still think the Antarctic ozone hole could potentially have been announced in
1981 rather than 1985. The BAS team could have saved two years if the data backlog had
not developed, and up to another two if the team leader had been a bit less cautious. His
caution in the circumstances cannot be seen as inappropriate though, particularly given
the failure of the NASA monitoring.

NASA’s problems arose from the sheer size and inaccessibility of their data set.
Scientists generally, and meteorologists most particularly, usually think that the more
data you collect the better. But very large data sets cannot be comprehended by the
human mind. Our unique pattern recognition facility cannot be brought to bear. Any
attempt to summarize to make things clearer involves making assumptions about the
nature of the data. Even local averaging and smoothing, for example, presupposes no
significant short wavelength structure.



Proc. ICHM 1.1 (2004) 105

There is a second, and closely related problem that also often affects
meteorologists. The danger of overlooking important structural features in large data sets
is exacerbated when the data is seen as routine, and when allowance is not made for the
possibility of surprises. Not only was the NASA dataset too large and inaccessible for a
general overview. It is also clear that no-one at NASA was briefed nor saw it as part of
their role to try to take such an overview.

Endnotes

1 This article draws heavily on material published in Maureen Christie, The Ozone
Layer: a Philosophy of Science Perspective, Cambridge, U.K., Cambridge University
Press, 2001. Chapter 6.

2 J.C. Farman, Gardiner, B.G., & Shanklin, J.D., "Large Losses of Total Ozone
Reveal Seasonal ClOx/NOx Interaction" Nature, 315 (1985), 207-210.

3 S. Chubachi, "Preliminary Result of Ozone Observation at Syowa Station from
February 1982 to January 1983", Memoirs of the National Institute for Polar Research
Special Issue, 34 (1984), 13-19.

4 Richard E. Benedick, Ozone Diplomacy, Cambridge, Mass., Harvard University
Press, 1991, p. 19.

5 Richard S. Stolarski, Kruger, A.J., Schoeberl, M.R., McPeters, R.B., Newman,
P.A., & Alpert, J.C., "Nimbus-7 Satellite Measurements of the Springtime Antarctic
Ozone Decrease", Nature 322 (1986), 808-811.

6 F. Pukelsheim, "Robustness of Statistical Gossip and the Antarctic Ozone Hole",
Institute of Mathematical Statistics Bulletin 19 (1990), 540-542.

7 Especially the Quasi-Biennial Oscillation. See, e.g. J.C. Farman, "Ozone
Measurements at British Antarctic Survey Stations", Philosophical Transactions of the
Royal Society of London, B279 (1977), 261-271.


