Oral History Transcript — Dr. Jon Shanklin
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Jon Shanklin; October 7, 1999
In this interview, Jon Shanklin discusses his involvement in discovering the Antarctic ozone hole. Topics discussed include: British Antarctic Survey; ozone layer observations; Dobson spectrophotometers; Halley Research Station / Base Z; Jon Farman; Brian Gardiner; Shigeru Chubachi.
Today is October 7th, 1999, just after 11:00 a.m. My name is Steve Norton and Iíll be interviewing Jonathan Shanklin regarding his involvement in discovering the Antarctic ozone hole. Just to review what we already talked about, the interview will be taped, transcribed, and once itís transcribed youíll have a chance to make additions, corrections, deletions, whatever before itís archived at the Neils Bohr Library at the American Center for Physics. Okay?
Norton:Letís begin by just getting some background — your educational background and how you came to work at the British Antarctic Survey.
Shanklin:In the U.K. I went to a school in a place called Chester. My parents were both geologists; I sort of followed the sciences line. I passed all my A levels, which are the U.K. exams before you go to university. Then I stayed on for an extra year to do S Levels, which are really only required if you are going to Cambridge universities. And I did reasonably well in those to get accepted at Walden College Cambridge of Natural Sciences. Natural Sciences are sort of an umbrella of all the sciences, really.
Norton:What year did you go there?
Shanklin:I went to Cambridge in October of 1973. So thatís twenty-six years ago. And did math, physics, chemistry, and geology in the first year, and then physics and geology in the second year, just physics in the third year, although I specialized in the geophysics side of things. Then I got quite an interest in astronomy, but the academic results werenít good enough to do a Ph.D. in astronomy, so I went into teacher training with the view to becoming a teacher. I did whatís called the first graduate certificate in education, and after completing that I was looking around for jobs both in teaching, but also was looking at some general physics related jobs, and just happened to see a job advertised for the British Antarctic Survey in Cambridge that quite appealed to me because it involved computing physics, meteorology, and those were all the interests that I had.
And this around 197...?
Shanklin:This would be í77. I applied for the job, was interviewed, and I went and had a phone call saying did I want it because the first person had turned it down. I said, ďYes, I want it. Iíll take it.Ē
Norton:What was the job for?
Shanklin:This was basically almost a dogís body type job where I was looking at radiation charts which were being digitized, and it was doing all the corrections and working out what had gone wrong all the way down the line. Looking at meteorologic observations coming back from the Antarctic. Again, checking around to see which had been coded correctly, whether it was actually seeing what they said they saw and so on. The third component of it was the ozone observations, which at that time they just didnít have the staff to fully work them up, so we were in the process of getting them on to computers.
Norton:Digitizing and processing?
Shanklin:This is really just manually typing in there as observations, and then I went along and processed them all on the computer. And we sort of work from the present backwards. We know what it was in the 1960s because it had all been worked up in Joe Farmanís book, which I guess youíve seen a copy of.
Norton:Yeah, that was the one that was with Hamilton?
Shanklin:Yes, right. So it was then just a question of initiative as far as getting the radiation data all sorted out. That was fairly tedious is the only way to describe it. But if you just kept all that in, it was possible to work through it all. So we completed the three bases up until 1982 I think was the last year that I got all that sorted out. The whole thing was an ongoing process because the observations were coming in every day, so we needed to do that.
Norton:What sorts of things were you doing when you were processing that data?
Shanklin:Which particular? The radiation or the ozone?
Shanklin:The ozone data, the first task was checking has it been typed in correctly. So we had typists who were keying in the data.
Norton:So you check it against the forms that actually came back or?
Shanklin:No, what we did is just check that all the observations were within range of this volarad [?] radiation numbers, that the format was correct with the sequences and numbers all made sense, and that there werenít any obvious problems. Then the next stage is to work out the ozone amounts from them so they make sense, and then work out if they donít make sense why they donít make sense. And thereís a whole variety of reasons from the immediately obvious ones that the typists havenít read the writing correcting so ones and sevens are quite easy to confuse. Things like that. So just checking that the typing has been okay. But then whatís been written down may be wrong as well, and that is a particular problem for a good part of our record where the station keeps whatís called kitchen time — the time shown on the local clocks. But the observations are done in universal time, and very often they would write down kitchen time and not the universal time.
Norton:You have to go back and look up.
Shanklin:So you have to work out which ones they got wrong that way. So that was a deductive process. Other standard things that they did wrong, the observations get numerically coded as to what type of observation it is, and they might write down the wrong code. So a lot of the typists typed it in correctly; the actual observation time is not what they did. So you have to work it out from the actual number.
Norton:Itís like a direct sun observation.
Shanklin:So a direct sun observation they might have coded it as an [???] observation. And initially the two may actually give ozone amounts that look sensible, but itís only later when you do the more detailed processing and things like that sometimes fall out and we think, ďBut his Langley plot was this point thatís way off the plot. I donít know what we could have done. Oh yeah, we got most of the observation times all the way around.Ē
Norton:So by looking at the Langley plots you could tell what someone had coded?
Shanklin:The Langley plots certainly tell you if itís coded wrong. Some of the Umcare [?] plots may plot [???] observations to get the sort of code. Again, if youíve got a point thatís way out it may be that theyíve actually done a direct sun observation and coded it as an [???].
Norton:So if youíre doing an Umcare and youíve got the profile you can have values —
Shanklin:This isnít so much getting the profile; itís just getting the sequence of observations because the actual dial reading should be a reasonably smooth curve. So itís not looking at where the ozone is in the atmosphere; itís just looking at pure observations and do the observations make consistent sense. Like if youíre just looking from observation A to B to C. If A and C are consistent where B is sort of way off and you think, ďWell, if it was down low it would fit.Ē You can sort that out. Another way is they sometimes write down a number like 1100 when they mean 1010. After a while you get to pick out these common mistakes and can then go back and say, ďWell, clearly theyíve done that.Ē Youíve seen them on the Dobsonís in the science museum?
Norton:No, not yet. Iíve seen them out at Boulder, though.
Shanklin:Right. All ours still will use human operators. We donít have to go out and read the dial. There seems to be a tendency to get a left right confusion. So, for instance, where number ought to be where it is 980 theyíll sometimes write it down as 1020 and visa verse. So they can see that itís about 10 and they just go the wrong way. And again those you can identify. And then thereís some that you just canít work out what in the heck it was that they did at all, and they just have to be deleted from the data.
Norton:So measurements like that when you actually calculate the ozone values get just really weird numbers?
Shanklin:Yeah, and they get bent because you have to come up with something thatís so unlikely so that two or three things they might have done wrong in order to get out a sense blows them out. I think one thing that they might have done wrong, fine. Two things that they might have done wrong, if youíre absolutely certain that is what theyíve done wrong, but three things is just too — obviously it would seem that it was some unexplained error they might have brought one of the levers in the wrong position, and like that you canít recover the ozone amount.
Norton:When youíve gone to calculate the ozone values, have you gotten any like really ridiculously high or low?
Shanklin:Oh, yeah. I mean sometimes you get such a virtually zero ozone values or sort of six hundred Dobson units.
Norton:And itís supposed to be about three hundred or so?
Shanklin:Well, it just doesnít fit in. Also, they are usually doing a couple of observations at the same time, and theyíll certainly find observations a day are standard, and you need to make certain the observations are all reasonably self-consistent. Now initially, we were just doing a very rough check on all the data because weíve got about ten yearsí worth. But since then Iíve been, over the years, just going back and doing more and more detailed checks and bringing all the different types of observations into closer agreement. Itís things like that which really take a long time, because when weíre doing the instrument calibrations you canít say that at this point the instrument calibration is so much. You need to wait until youíve gotten another few yearsí worth of data and then do best fits to say, ďRight at that point the calibration was so and so.Ē So I would say that five years agoís data, weíre getting pretty close to what it will finally be, but it is still room for a little bit of flexibility. The other thing is that computing powers continually increase. When we first started entering the data onto the computers they were fairly limited in ability. It would take some places half an hour just to compile a program that you wanted to use to analyze the data. And so that meant that you didnít make many changes to it, and the sort of statistics and so on that you could do were pretty limited. Now on PC you can run the same thing in a few seconds and see exactly whatís happening to all the data, and the statistical packages are better. The long-term goal is to do further improvements before we finally lodge the data with the World Data Center. But in the meantime itís all available in the real time for people to see when they want.
Norton:Now, you spent two years down in the Antarctic, too?
Shanklin:No, I probably have in total spent two years down there in Antarctic if not more than that, but Iíve never actually spent a winter down there. Itís just summer visits. The first visit was in í81, í82. And that turned into a somewhat longer visit than expected, thanks to Dobsonís Law, which started while I was down. So I had to sail all the way back. But that first visit down, the primary task was to take down the new Dobson data.
Norton:It was 123?
Shanklin:Yes. And compare with the existing one down there, which was number 31.
Norton:Well, can we take a step back here for a second?
Norton:Why was 123 ordered? Was it simply because the other ones had been out in the field so long and you didnít have a spare? I mean it wasnít anything like you were getting the low values.
Shanklin:What we wanted to do at that time was really we got the three stations: Howie, Faraday, and Great Lichen, and we had an instrument at each of them. And having an instrument at each of them meant we had to stay there because we want continuity of observations. So buying a fourth instrument that we could start a rolling program of putting a new one in at one station, bringing the one out, getting that overhauled, send it down to the next one, bring that one out. The idea was we would then have a rolling program overall so that we could be reasonably confident that the instruments were all in tip-top condition. I think probably, looking back on it, that would have worked quite happily, but I think my view now is that we really want to leave an instrument in place for at least ten years in order to get good calibration in situ, rather than having a more frequent program in exchange with the U.K. I think if weíd followed the original idea the instruments wouldnít have been down in the Antarctic long enough to get a good in situ calibration.
Norton:Will you give me a feel for this? I donít have a good understanding of why having them down there for ten years as opposed to five years?
Shanklin:Basically because we do our calibrations using the Langley plot technique. So our instruments are all, if you like, divorced from the world standard. The main reason, I think, for that is that we consider that weíre isolated. We want continuous observations. If we took an instrument out to compare against the world standard, weíd probably have no Antarctic observations for two years or something like that because thatís the length of time that it takes to exchange the instrument. Also, during the transport of the instrument because itís going to shift and thereís going to be lots of vibration, and thereís no guarantee that the instrument that you had in the Antarctic, the instrument that you compare against the instrument you take back to Antarctic, is actually the same. I would say thatís a failing with the present system. But yeah, itís nice to have all the instruments side by side and see if they are really the same thing. But can you guarantee that what weíre comparing is what we actually measured after the shipping? So ours, because weíre doing it with reverse principles, weíre pretty much convinced that even though weíre floating from the world standard, we will be matching that standard. Our feeling is certainly that was true when we took the, first of all, 123. We compared against med officeís regional standards.
Norton:Did you do that work?
Shanklin:Yes. And then my instrument, number 123, went down to Antarctica and we took 31 back and we compared that against the Meta standard. But the matter of which weíre continually tinkering with the instrument. Saying, ďWell, thatís not quite an adjustment. Weíll make an adjustment now,Ē or, ďThereís an improvement needed there.Ē So I donít think they ever knew what their standard was, and that I think now has been pretty well documented. Their standard wasnít at all standard. It was subject to shifts in calibration every time they touched it.
Norton:Did you know this back in í81 when you were actually doing this comparison with their standard?
Shanklin:We had suspicions that if anything it would be better for the med office standardizing against than vice-versa. What we could establish was that our calibration agreed with theirs within ten percent or so. So we were happy that we werenít a long way out, and we were happy that they werenít a long way out.
Norton:So this is going to take a rough estimate check on the new instrument then?
Shanklin:Yes. Also it helped once weíd got the 31 and 123s side by side and they were both giving the same answers.
Norton:It was done at Howie?
Shanklin:This was done at Howie. Then again, you could be fairly confident that it wasnít an instrumental artifact because weíve got U.K. instrument 123 agreeing with 123 agreeing with 31 agreeing. In fact, really weíre suggesting that the measurements were okay and that any change in ozone that weíre seeing, weíre really in the atmosphere.
Norton:Now, how long did the 123 and 31 sit side by side down there?
Norton:For two weeks?
Norton:And 31 got shipped back?
Shanklin:Yes, because that was all the time that we had to release that. So the ship didnít stay very long. Nowadays, the ships stay a lot longer and we could probably have them side by side for two months or three if we got the timing just right.
Norton:So you went down with it?
Shanklin:I went down with it. This is my first visit to Antarctic. This is all exciting and new. Itís still often exciting and new. I donít think any of the trips that Iíve been on have been identical. Weíre always doing something different. But it was really great because I was going to be there in the Antarctic actually doing ozone observations. I sort of knew the theory that I could do it, and so doing it in the Antarctic was really great. The hut that we had 31 in, it was pretty small, there was only room for one instrument inside it. So weíd have to have the other one operated the outside and we put a bit of cardboard down on the floor on the snow surface and had the instrument on its trolley sitting on the snow. That immediately gave us a few problems because we operating in about minus twelve Celsius. The instrument had been calibrated in terms of wavelengths, which in the U.K. I think the temperature range were 15 to 25, something like that. So we were way outside that calibration.
Norton:And the 31 in the hut was kept in that range?
Shanklin:31 is more or less constant temperature. Because it had been there for a long time we knew what the temperature coefficients for the [???] thatís essentially what we were looking at. But it became very clear that the temperature coefficient we were using, most of the D wavelengths were out, so we had to reestablish what temperature coefficient was.
Norton:That was for 123?
Shanklin:Thatís 123. 123 was a new instrument, and the manufacturers couldnít obtain natural cords for the prisms and the optics as a whole, so they fused cords and it turned out that the temperature coefficient for that fused cords is the opposite inside and twice the amount of the previously used natural cords.
Norton:I think Bob Grass had mentioned something about this.
Shanklin:Because weíd cool it down to such low temperature that actually gave us quite a good feel for what the temperature coefficient should have been. The way we do that is from the sky plots we scan the Q lever through the wavelength absorption and get your curve, which goes down and up and down again. So you know, again, if the first principle is, what the wavelengths should be on real sky, whereas, many organizations just use the mercury lamps, mercury and helium and all the other standard emission line lamps to do their calibrations. We prefer to use real ozone. So again, thatís something that is slightly different between us and many of the other organizations.
Norton:When you got 123 did you know it had the fuse quartz?
Shanklin:We knew it had fuse quartz.
Norton:But you didnít know the coefficient was different?
Shanklin:We knew that the coefficient was different because the manufacturers established that at a workshop and they gave what they felt were the coefficients.
Norton:And they werenít quite right?
Shanklin:They werenít quite right, and they were particularly wrong in case of the D wavelengths.
Norton:Now, you identified this problem when you were doing calibration at the med office?
Shanklin:No, this wasnít until we got down to Howie.
Norton:How did that actually emerge that there was the problem?
Shanklin:Because we were doing these sky tests, and the result that gave when the instrument was at minus twelve was vastly different from what you would get by extract lighting. So it was clear.
Norton:So the total ozone you were deriving?
No, the, it was in a sky — if Iíve got to any to hand... I know this is an actual one from 1982. This is í92 when we also took 123. This is [???] in the U.K. But basically what weíre doing is weíre adjusting the position of the Q length versus the D wavelengths and looking at what dial reading you get. So as you come down you get a minimum up to a maximum and then down again. The actual setting for that particular pressure and temperature should be right about there. So we said a 106.7 is the middle. This is the actual ozone absorption for the D wavelength. Itís a fairly well defined and quite deep absorption light. Itís quite easy to plot. You measure what the temperature is, what the pressure is, and you also know from the manufacturersí tables what you expect. So this is the Q value from the tables. In this particular occasion is point A to a degree different from what it ought to be. This is where we took two of the instruments at the same time. This one is number 73, and again, thatís 1.1 degrees. So the value drifts a bit with time. So what we did was one of these tasks where youíre just looking at [???] wave and you move the Q lever down and then back up again and you just scan through this absorption light. Iím doing this at a sort of a minus ten temperature. Howie was not just a little bit out it was sort of two degrees out, and that was sufficiently large. I was sure it was an experimental error, and so the only logical thing was a temperature coefficient.
Norton:So then you adjust —
Shanklin:Adjust the temperature code coefficient, and then you have to redo the ozone observations because the observations prior to that. Particularly the very low temperatures would be inaccurate.
Norton:You have this table when you take the measurements, you pull out the thermometer, do the temperature reading, and then check the chart on what the coefficients should be and thatís what you use?
Shanklin:Thatís what we used then. I mean, nowadays itís on the computer so you just type in the temperature and type in the pressure and it does all the calculation for you and it sets the Q lever, too, for its value. So you canít do that.
Norton:So you identified that then when you first brought the instrument down?
Norton:So it was 123 that was actually down there doing the measurements in winter í83, í84, í85?
Norton:So 123 wasnít sent out — there was no additional instruments sent down there when you were getting these low values in those winter months?
Shanklin:What? So that weíd have two side by side at the same time? No, that was never the plan, because a Dobson is a Dobson and thereís no real point in having two side by side throughout the year if youíre convinced that theyíll record the same in the summer. What we would have done, if when we took it down they had given vastly different readings, Iím not quite sure. Fortunately, that didnít arise. But if we put the two side by side and theyíd been fifty percent different then weíd perhaps do some serious thinking as which oneís wrong. But as it was they agreed and the question didnít arise.
Norton:The reason I was asking the question is because a number of things Iíve read say that the reason you brought the instrument down there was because you were getting low readings.
Shanklin:That was a little bit. We certainly wanted to confirm there was nothing wrong with the instrument, but this purchase had been planned irrespective of that to a large extent.
Norton:So when was it that you first started noticing the downward trend in the data?
Shanklin:In the late í70s, really, but I suspect a lot of my present perception is colored by things that have gone on since then. Whether thatís an accurate recollection of what it really was at the time Iím not certain. But we had an open day at the survey where the public was going to come in.
Norton:What year was this?
Shanklin:Iím not certain of the exact year. Thatís one of the things thatís faded from memory. It was certainly when I was working on the ozone data and also when there was lots of concern that aerosol cans would destroy the ozone. To some extent I thought, ďWell, thatís a load of rubbish. How on Earth can aerosol cans possibly destroy the ozone layer?Ē Weíve got data in the Antarctic and Iím working on this yearís data. Weíve got data from ten-ish years previously. Iíll do a comparison of the two and that will reassure everybody. The problem was that the October values in particular were quite a lot lower than they had been earlier. Weíd been experimenting with extending the observations season by changing from CC dashed to CD observations because you could do those at high [???] values. So the observations werenít a hundred percent comparable with what had been done earlier. So it could have been an artifact, but it certainly seemed to me that maybe something was happening. And also, occasionally the guys on base would say that the ozone values look a bit on the low side.
Norton:So you think this is around the late Ď70s?
Shanklin:This is certainly the late Ď70s. Then what really happened then is that the process in the radiation data was coming to a close.
just doing a fairly rough calculation of what it all was. I think I also went to Joe to say, ďLook, this is really exciting. The values are low in October.Ē He said, ďI know. October values donít really count because the winter time ozone values were all really indeterminate. His view was that youíve got the spring warming that just swept out and in. It just affected the winter values depending how much spring warming you got, and that wasnít predictable. So October values werenít predictable. You might get two high years and then two low years. I think his view was also colored by the Hamilton paper, which had looked at the day-to-day variation in ozone amount and identified the southern autumn as being the best time for detecting changes in ozone because the day-to-day variation is least in the autumn. So February, March time, maybe even January was the time that weíd see any changes was October, November, because the timing of the warming was quite variable. But values could be high or low.
Norton:This is what Brian Gardner had mentioned that in the Ď70s when Roland and Molina — all these predictions that fluorocarbons would be bringing down the ozone. Thatís when you looked for it initially, was February to March.
Shanklin:Yes. I didnít really have any preconceptions as to what should be high or what should be low. I was just looking at it from the point of view of an observer who had no theoretical background at all. But I was a physicist, so I was sort of looking at the data. It certainly struck me that October seemed to be low in the years that I was looking at compared to the previous data. At that point it would be fair to say there was nothing systematic about it. Just one year, and as Joey [?] said, ďOne swallow doesnít make a summer,Ē to use an English proverb. So it sort of got left at that for a while. Then the following year October values were, again, low. He still wasnít convinced. But again, in the background weíll still be doing all the processing of the 1972 through the current batch. And at that point I began to focus on the Howie data rather more and started getting through it as much as I could. And was then able to demonstrate pretty clearly that it was a systematic event, which each October weíre getting lower and lower values.
Norton:You could tell it wasnít a calibration problem or anything?
Shanklin:Iíd gone through all the calibrations and was reasonably happy that they might only be accurate at the ten percent level, but this effect was above any reasonable noise.
Norton:And you still think this was prior to you going down with 123?
Shanklin:No, this is after.
Norton:So this would have been?
Shanklin:í82 or í83, something like that. This is my original discovery paper, if you like. This is where weíre going.
Norton:You wrote this up?
Shanklin:This I wrote up and used it to convince Joe and Brian that it was happening. And I submitted this to both Brian and Joe and Michael Wycoft [?], who was the head of the division at that time. Michael came back with all sorts of changes and Joe went away smoked his pipe and thought about it. But basically, the key thing was the values did seem to be dropping.
How did you determine this down [???] ?
Shanklin:Just [???] squares. That was a January launch I thought was going down, but maybe not. But this was the October one, which is pretty clearly going down.
Norton:So this would have been in the fall of?
Shanklin:This started in November of í84. That was what kicked everything finally into action to get the Nature paper sorted out. Prior to that —
Norton:Can I get a copy of that?
Shanklin:Yes. Iíd actually written to Harry Broxom [?] at Wallace, and was 5.2 or something at the [???] level.
Norton:And this was about the low values?
Shanklin:This was way before we published in Nature, saying that the values are definitely low. I thought, ďWell, is it El [???], which had gone off rather at that time.Ē Weíd actually asked them here, ďIs it confirmed by such a [???] ?Ē
Norton:And they pretty much wouldnít have known.
Shanklin:Well, they should have done because we were doing comparison observations for them. We were doing ozone observations to coincide with sun light and over-passes specifically to calibrate satellites. So we were doing these special observations for them, and we thought they really ought to be able to tell us whether the satellites were agreeing. I guess we were lucky that I only had one reply to that from this guy and that group is no longer involved. So if theyíd actually bothered looking at that point they could have beaten us into the [???].
Norton:As Iím finding out, people down the hall didnít know what was going on in the ozone processing.
Norton:This is very perplexing, because as the story goes, your paper comes out, NASA went back and reprocessed it and found the hole. But as I found out, they actually identified it in July of í84. But the problem Iím having is that it shows up in the previous years, but they didnít identify it prior to the summer of í84 and Iím having a little bit of difficulty understanding why they didnít.
Shanklin:I think probably itís just having somebody look at the data, because very often itís how you are looking at observations that govern what you see. I was just looking at it almost with a blank slate and Iíve got no idea what to expect. And possibly having the long gap where we hadnít been doing anything was a help because it was unclear that the October I was looking at were different from the earlier ones.
Norton:The long gap in the process of the data?
Shanklin:Yes. Whether it would have been as obvious. It ought to be as obvious if weíd been keeping up with things, but especially if we were doing it operationally as process data you wouldnít look back quite as much. Youíd only look at what youíve got now.
Norton:So mostly finding out thatís what was going to maybe go with the Nowa [?] people.
Shanklin:So largely said, thatís what you do with operation meteorology. Itís the observations that theyíre making now that matter because thatís what you want to use in the forecast. Itís all real time stuff. What it was ten years ago and whether this yearís is different than ten years ago isnít really relevant. And I think thatís one of the problems with the climate change debate. That most of the meteorological measurements are not made with the use of detecting climate change. Theyíre there for forecasting purposes so that you can get a good picture of whatís going on now. And if we were doing it for climatic purposes we do it in a very different way. I think thatís probably true of the ozone instruments. That the interest was whatís going on now rather than is it changing.
Norton:You were looking at the autumn values. You werenít really seeing anything there. Maybe a little bit, but the October values where you really saw it. You said you were focusing on the Howie Bay data. This shows up in the Faraday data, too.
Shanklin:It does, but not as clear.
Norton:Now, did you see it in the Faraday data before?
Shanklin:At about the same time, yes.
Norton:It just wasnít definitive enough?
Shanklin:Itís not so clear cut. What I wanted to do was show here this is concrete and highly significant. The Faraday stuff was significant, but less so than Howie, which is why itís always focused on Howie.
Norton:Is the problem with the Faraday station that it can be inside the hole? Outside the variability is much greater there?
Shanklin:Yes. And also you can get very large changes from even one day to the next. It can change by fifty percent or more from one day to the next at Faraday. Whereas at Howie the day-to-day variation is very, very much smaller than that.
Norton:Now, prior to the early Ď80s and the Ď70s when we were talking about the CFCs and all of that, do you recall having conversations with Brian Gardner, Joe Farman, about looking for this stuff from the data? Or do you do this on your own?
Shanklin:I think it was really only sort of outlines that the autumn was the best time to look at changes. But it would be sort of nice to find something in our data, but we thought it would be fifty or a hundred years in the future before anything significant was there. I think it was a vague conversation about the big solar proton event in í79. Iím not sure of the exact date. Big solar proton event, which somebody said it affected the ozone layer. We couldnít see anything in our data, but then it was only supposed to affect the very top upper most part of the atmosphere anyway. Thatís, as far as I can recall, the most we talked about it.
Norton:So youíre looking at this stuff then was pretty much you were involved in processing all this data.
Shanklin:My job was to get the data processed and make the final report as accurate as we could.
Norton:It started emerging in your consciousness. People saying values getting lower, youíre noticing it —
Shanklin:Yes. And sort of putting two and two together, and well, it looks like there is something here. So the next step is can I actually demonstrate that itís significant and [???] document. Yeah, I could. And it was really that, I think, that convinced Brian and Joe, that yes. And they then thought, or particularly Joe felt, that itís no good just publishing observations. Youíve got to explain whatís going on as well. So he then went and looked at his model with a view to trying to use that to explain what was going on.
Norton:Thatís one of the things that held the NASA people up. Well, in the paper it says, ďTo interpret the difference as a seasonal instrumental effect would be inconsistent with the results of routine checks using the standard lamps.Ē Can you comment on that? And also the fact too that youíre having a seasonal effect here. Just prima-facie seems to suggest that itís not an instrumental artifact. So could you speak to how you could think that a seasonal effect was an instrumental artifact?
Shanklin:It could be related to temperature, for example. But in general it will be somewhat colder in the atmosphere in springtime compared to the autumn just because of the seasonal lag in solar effects.
Norton:In that case wouldnít it be symmetric at the beginning of the spring, the end of the autumn when it starts to get cold again?
Shanklin:Yeah, so you might expect to see some symmetry there, but it could equally be an environmental if the temperature instrument was changing from spring to autumn. So that could introduce a bias or low —
Norton:So itís changing from cold to warm as opposed to warm to cold.
Shanklin:Although, the fact that the instrument is in a thermostatic hut and thereís no evidence for it changing. But that was a possibility, and those sorts of things should be shown in that monthly standard lab tests that we do, which are looking at the long term calibration of the instrument. If the processes werenít [???] youíd expect to see it fairly clearly. There was obviously no trace of seasonal effects in that. But I think that needed to go into the paper saying that weíd looked at all that.
Norton:Blocked that possible interpretation. Now, what about the fact that the instruments cleaned over the winter? Was there a thought that maybe there was something —
Shanklin:That it could be getting dirty. That certainly could be a possibility except that if it was, again, youíd expect to see a jump in the standard lamp readings.
Norton:And that wasnít showing?
Shanklin:When you do get a jump generally what happens is that all three wave lengths seem to jump together. So because largely weíre basing this on AD or CD observations, those effects get taken out of the equation. Again, that was one reason for wanting to go away from the CC dash type observation because thatís just using single wavelength. So it can swing as individual wavelength calibrations change. But using paths that [inaudible] together and youíre subtracting A from B. That just cancels out, which is one of the really neat things about the way the instrument works. But by and large, everything that you can do wrong cancels out so that really demonstrates the brilliant design of it.
Norton:Are there any other potential problems that were considered that might be going on with the instrument?
Shanklin:Observers. And that can play a part, but again, we change them every two years. Seems to be independent of the actual observer. The orientation of the instrument, it had always been aligned correctly with the sun when youíre doing the observations, and maybe in the spring they werenít doing that and in the autumn they were. So that can release a slight variation in measurement.
Norton:How was that ruled out?
Shanklin:Largely by experiment and demonstrating that it only makes a few Dobson units difference. So thatís well in the noise.
Norton:Something like that, was that done here?
Shanklin:No, it was done in the Antarctic.
Norton:So you actually asked them to locate the instrument, see if that produced any —
Shanklin:We did sort of start writing it for a little bit that it is important where thereís any observations to make sure itís aligned. There was a procedure for the direct sun observations, but usually it sort of left [inaudible] observations whether you need to align the instrument or not.
Norton:You wrote this paper up November 2, 1984. You submitted to them and things switching to publication. After Joe Farman and Brian Gardner read this, what sorts of conversations did you have with them?
Shanklin:I would say almost deafening silence, if you like. They really sort of just went away and dotted the Iís and crossed the Tís on everything, and it was really getting me to check the data one more time. Is it all a hundred percent? And then to draw up the graphs demonstrating it. I think Iíd used the lowest springtime value and I also used the lowest October value. So thatís a little slight difference in emphasis.
Norton:They were becoming convinced after you read this. They didnít just automatically, ďOh, yes. This is real.Ē Or did Joe Farman need a little bit more convincing?
Shanklin:I think Brian had to keep on at Joe to get him to think about all the possibilities and also to get it into print. Joe would have gone on forever making sure that everything had been thought about and there werenít any possible errors, whereas I think Brian saw the need for urgency and get it out as soon as we can.
Norton:Do you recall when the paper was actually sent out?
Norton:Iíve gotten some dates from —
Shanklin:Brian. Brian actually put it in.
Norton:Kind of triangulate on things because heís pretty sure, but not one hundred percent sure. Now, the paper goes off to Nature. Were you talking about this to other people in Cambridge at the time? Were you getting feedback from people?
Shanklin:Not in my case. We were sort of talking about it with the Antarctic observers because they were the ones making the observations. I think they were surprised that it took so long to get it to Nature.
Norton:So in between the time it went to Nature and the time it actually came out was there much talk around that youíre aware of about this?
Shanklin:I really donít recall anything particular. It was really sort of feedback from the referees that wanted a few points clearing up, but that it was generally positive and they liked it.
Norton:You didnít get involved at all in the discussions of the explanation of this effect?
Shanklin:No, I was the observer, and here are the facts. Youíve got to explain it.
Norton:How do you feel about the ability to say that thereís actually something there? A real effect when you havenít dealt with all these other theoretical possibilities that Joe Farman wanted to look at?
Shanklin:I think largely from knowing how the observers operate and the way the Dobsonís functions itís very, very difficult to get something that happens in October that doesnít happen in March. At that time, there wasnít any trace of any changes in March. So it really had to be a seasonal thing. It seemed fairly clear to us that it involved CFCs. Although the graph that we published in Nature was an artifact, if you like. We carefully adjusted the axis to match, which probably we shouldnít have [???].
Shanklin:Yes. And also possibly in reverse for CFCs increasing matched the ozone decreasing. That really did seem to be the only plausible change in the atmosphere. At that time I donít think we thought about [???] in the slightest. We knew we had them and to some extent we perhaps — Iím not sure whether we actually thought they were becoming more common at that time or not. I think probably that came a little bit later.
Norton:But so far as the data you had from the Antarctic, it was showing that you have this drop in the ozone, but there was no real significant changes in the dynamics of the polar vortex? Or could you tell that from your data?
Shanklin:Not from the ozone data by itself. Temperature data really didnít show much in the way of changes, but itís pretty messy. And also we changed [???] systems, which you couldnít then be certain whether it was a change in the atmosphere or a change in the instrument. But again, itís something thatís good about the Dobson measurements that were being used. The same instrument since 1956 with the same techniques, but again, we made it pretty clear that it really couldnít be an instrumental artifact. Which is perhaps what the space base people couldnít be so certain about, because they keep launching the satellite and theyíre using the latest technique to do the measurements. So one of the changes that they were seeing due to a new satellite to the atmosphere. And I think also that the space base people think or it must be due to the sun to some exchange and we had satellites up to six years and the solar cycle is going down so the ozone is going down. And they appeared not to be willing to consider a longer historical record, which went back over the sort of thirty odd years at that point.
Norton:Are you talking about ďtheyĒ as people at NASA, or just the scientific community in general?
Shanklin:Iím not sure if itís NASA or the scientific community in general, but certainly the space base community seemed to want the sun as the mechanism.
Norton:Like the solar proton events? Things like that?
Shanklin:Yes. Weíre saying that as part of solar cycle, clear correlation. Because they only have the data for half a solar cycle. So I think our view was thatís not very physical and you canít draw any conclusions about correlations on half a solar cycle. There are people still doing that. Theyíve got half a solar cycle or two solar cycles, but with all this wonderful correlation.
Norton:So you think you data could strain the situation, especially to include that in interpretation?
Norton:Youíve heard of Shigeru Chubachi, right?
Japanese polar researcher who reported low values in í84?
Norton:What are your feelings about his reporting those low values and what he was up to as opposed to the results you got at Howie Bay?
Shanklin:He couldnít draw anything conclusive out of it because they didnít have a continuous record. I think heís got a few spot measurements.
Norton:They had been taking measurements at Showa us since 1966, right?
Shanklin:Yes, but nothing like ours, as long as ours. And also Showa is not as well placed as Howie was. Howie tends to be closer to the ozone hole, so we tend to get lower values.
Norton:So the low values, they were getting — could have been due more to planetary waves and things like that?
Shanklin:No, I did actually look at most of the over Antarctic solutions from the red book.
Norton:Around the time you were looking at your data?
Shanklin:Yes, because we wanted to find out whether it was just us or everybody else. I think most of the others showed reasonably plausible for decreases, but nothing like as conclusive as the Howie situation. I think I wasnít aware of that paper until long after the fact, but I was aware of the Japanese data and the red book.
Norton:Being a bit low.
Shanklin:And that was low as well.
Norton:You checked and they did have profile data from Showa. Did you look at that at all or were you just not concerned since you were only doing total ozone?
Shanklin:We werenít particularly concerned about it. We had our own profile data from Faraday. [???] have been Howie. That didnít really show up anything terribly clear cut.
Norton:So youíre saying then that these other stations were showing some decreases, but it wasnít —
Shanklin:Only because their record was patchy or it doesnít begin early enough at the South Pole. They canít make out any measurements until most of the ozone hole is gone just because of solar elevation. Or the stations on the other side are more affected by a spring warming at that sort of times. So they donít see it. So itís really very Atlantic side of Antarctica that is well placed for seeing changes.
Norton:Was there anything else in the processing of the data that caused potential problems for interpretation?
Shanklin:I donít think so. Once I got the computer programs roughly sorted out, then, provided Iíd done the programming right, that was it. And I think Joe and Brian worked through some of the results by hand just to make sure that there wasnít anything seriously wrong.
Norton:Brian was saying that they had looked at the direct sun observations because it was less potential for —
Direct sun observations are absolute, if you like. [???] are all by relation to the direct sun. So if you get a direct sun observation and just look at the direct sun as it shines on something, then you can be 99.9 percent sure that itís real.
Norton:So itís just less chance for things to go wrong with direct sun light involved?
Shanklin:And also the accuracy of the direct sun is better. A well done AD direct sun should give you ozone values to [???] percent. If the instrument calibration is correct.
Norton:Now, had you thought about doing that when you were processing the data?
Shanklin:Extracting out just the direct suns?
Shanklin:I was more working on daily means because I thought if the daily mean gives you something, then —