Saving our Skins: Chapter 15. The Things We Did
Atmospheric Reflections from a Lauder Stargazer
The continuing story of “Saving our Skins”. Catharsis through the things we did …
Updated September 5, 2021.
Our new UV studies at Lauder were already starting to bear fruit before David’s death. An early contribution was when we used our spectral measurements to demonstrate the inverse relationship between atmospheric ozone and sun-burning UV. In that paper, published in 1991, we showed that for every 1 percent reduction in ozone, sun-burning UV would increase by 1.2 percent. Just as predicted by models.
Another early discovery was more of a surprise. In collaboration with Gunther Seckmeyer we showed that biologically damaging UV at Lauder is nearly double that at a similar latitude in Southern Germany: a contrast far larger than anticipated. That paper was published in Nature in 1992 and was the start of a long and fruitful collaboration that continues to the present. Gunther and I don’t always agree, but we do share a mutual respect, and are continually testing our ideas and our humour on each other.
Our UV work was gaining recognition and our studies were answering questions in a rapidly developing area of research. I was invited to be lead author for the UV chapter of the 1991 WMO Science Assessment of Ozone Depletion. It was a fantastic opportunity to work closely with some of the world’s top atmospheric scientists. The assessments were led by NOAA’s Dan Albritton and NASA’s Bob Watson: both charismatically able leaders. Watson would later become chair for two IPCC Assessments of Climate change and would be knighted in 2012.
When the Steering Committee of the Network for the Detection of Stratospheric Change (NDSC) decided that UV radiation should be included in the Network, Gunther and I were elected to join them. Together we established the specifications needed for UV measurement systems to detect the expected long-term trends. Our own systems were among the few that could meet these demanding specifications, and as a result, we built and sold several new instruments for deployment at other NDSC sites (no conflict of interest there, surely!). They still form the backbone of spectral UV measurements in the Network, which was later renamed the Network for the Detection of Atmospheric Composition Change (NDACC) to encompass effects of climate change as well as ozone depletion.
At a conference in Japan a few months after David’s death I met Sherry Rowland (mentioned in chapter 3) who was by then a highly sought-after public speaker about ozone depletion. He’d read our 1991 paper with interest and I was flattered when he asked me for a copy of a figure from it to use in one of his talks. I was even more chuffed a couple of years after that to see that he was still using it in a conference keynote address. Soon after, in 1995, he and two colleagues jointly received the Nobel Prize in Chemistry for their pioneering work about the formation and destruction of atmospheric ozone. The other two were Paul Crutzen, from Mainz, Germany, who visited Lauder in 1999; and Mario Molina, then at MIT, who I met much later in his hometown Mexico City, during a UNEP meeting at nearby Cuernavaca in 2014.
Shortly before a trip to Washington DC for work on the Ozone Science Panel Assessment in 1994, I received an invitation to attend a meeting of another panel: the UNEP Environmental Effects Panel, who were meeting in Buenos Aires shortly after the Washington meeting. Because of the late notice, I didn’t have funding to attend. But when I asked my friendly travel agent, Bruce Robertson, how much it would cost to include a side-trip there from Washington, he said it would be only a couple of hundred dollars more. I decided to do it, expecting that living costs there would be low enough to not be a concern. I was wrong about that. The Argentine peso was pegged to the US dollar at the time, and everything visitors needed was expensive, despite the obvious poverty of the locals. Their lives must have been based around a different currency, perhaps revolving around bartering or trading.
The lead author of the UV chapter of the UNEP report was Sasha Madronich, from the National Center for Atmospheric Research (NCAR), in Boulder Colorado. After the meeting in Buenos Aires I was invited by the Panel chair, Jan van der Leun, to join them. When Sasha left the panel after 9/11, I became the lead author of the chapter he had led.
Sasha later re-joined the panel, and quite apart from our work there, we enjoy ongoing research collaborations. I took a sabbatical with him in Boulder Colorado in 1999, where he introduced me to the intricacies of his beautifully-written “TUV” Fortran code that calculates UV irradiance. It’s proved hugely valuable, and my Lauder colleague, Dan Smale, has become highly proficient at using it as an investigative tool to interpret UV measurements. In one definitive study we quantified the effect on UV of altitude differences between Lauder and the high-altitude Mauna Loa Observatory in Hawaii. In the same study we quantified the enhancement in radiation there due to clouds which often form a blanket below the observatory. We found that the increase in UV with altitude was much smaller than had previously been seen. Under these pristine conditions, sun-burning UV increases by only 5 percent per kilometre. But UV levels could also be further increased by up to 20 percent because of reflections from clouds beneath the observatory, a similar increase to that seen from the edges of overhead clouds under partly cloudy conditions. The UVI there sometimes exceeded 20, the highest value ever recorded at that time.
I stayed on as lead author for two more Science Panel Assessments (1994 and 1998) and remained involved as a co-author for a couple more. I was also lead author of the UNEP Assessment Panel reports until my colleague Alkis Bais, from Thessaloniki, Greece, took over in 2014. Although these tasks are hugely rewarding, they also represent a huge amount of work (and travel). I doubt if any other researcher has been lead-author of so many of these Assessments. Maybe others were smart enough to get out of it earlier.
It’s gratifying to know, though, that my work on these panels has contributed to the success of the Montreal Protocol. But, in doing so my carbon footprint ballooned, with travels around the world at least once per year since the early 1990s. One trip around the world approximately doubles the annual carbon footprint of Kiwis, so my footprint has been twice as bad as the average Kiwi for two decades. It’s been an interesting journey, involving visits to many countries. Paradoxically, the only continent I haven’t visited is Antarctica, the continent where the ozone story began.
While we might have been saving the planet from ozone depletion and its effects, we certainly weren’t helping to save it against climate change. But at least I tried to kill two birds with each stone whenever I travelled. In the late 1990s I joined an advisory group led by Gunther Seckmeyer that reported back to the WMO about UV instruments. Our task was to specify the UV instrument types and how to use them for specific goals. For example, the requirements for trend detection were much more demanding than for providing advice to the public about current UV levels. To minimise our travel, we scheduled those meetings to dovetail with other meetings or conferences. The work from the group resulted in a widely-read series of WMO reports published between 2001 and 2010, which have become Standard Operating Procedures for these various instrument types. For the simplest broad-band filter instruments, we showed that model-calculated corrections that depend on the amount of ozone in the atmosphere and the sun elevation angle must be applied to correct for differences between the instrument passband and the biological weighting function of interest. Without these corrections, errors from this type of instrument are large.
Our UV spectrometer systems, with their high spectral resolution, avoided that issue. That, and their high accuracy made them suitable for research and trend studies. Other UV research groups wanted them too. We’ve made a bit of money for NIWA selling them and then setting up ongoing projects to maintain calibration and data archival. Mike Kotkamp kept all those spectrometer systems working and calibrated - and he continues to do so now that I’m “out to grass”. Hisako Shiona later joined our team and her expertise with computer programming uncovered a few embarrassing errors that I’d made with the original data processing algorithm. Luckily none too serious. Her skills again came to the fore when we built NIWA’s often-hit ozone and UV web pages, which provide information to the public to help them understand and minimise their UV risks.
In 1992, a recent PhD graduate from South Africa, Greg Bodeker, had arrived at Lauder from out of the blue. He’d spent some time working in Antarctica and said he’d like to work with me. I was flattered but had to tell him that we didn’t have any money to pay him. He said he didn’t care and started working with us anyway. He turned out to be smart and hard working. He was far too good to “let go”, so Andrew Matthews found some money to keep him at Lauder. The first of our many papers together was published in 1993. I later found that he had another reason for coming to Lauder. While in Antarctica he’d met a young German researcher. Her name was Karin Kreher and she had just taken up a study position at Lauder. I think his desire to work at Lauder may have been more primordially motivated that just wanting to work with me.
Although Greg was young, he was already confident and proactive. He arranged for me (the leader of the project he worked on) to visit South Africa in 1995 to work with his old colleagues at the University of Natal, in Durban. They were challenging times. Their newly elected prime minister was Nelson Mandela, and there were a few social issues running hot. I was paranoid about getting sick or injured because all the nurses were on strike. And it wasn’t safe. Motorists in big cities like Johannesburg always kept their car doors locked and didn’t stop for red lights at night for fear of being accosted. Barbed wire entanglements topped high fences around houses in the well-to-do suburbs. I too became caught up in the climate of fear. I’d taken delivery of my first laptop computer just before leaving Lauder. Because I was concerned about security, I hid it in my bedding while I went out one sunny afternoon. Unfortunately its power supply suffered a terminal meltdown. I’d forgotten to turn it off and it had overheated in that confined space. I spent a good part of my remaining time there trying to repair it.
I have one unforgettable memory of the trip. At every hotel and bar there was a replay of the last 5 minutes of the Rugby World Cup final played there a few weeks earlier, when South Africa’s Springboks had defeated the New Zealand All Blacks with a drop kick goal by Joel Stransky in extra time, after an ill-conceived 22 drop out restart by his counterpart, our own Grant Fox. See, I told you I remembered it well. Most Kiwis felt cheated by the game. The All Blacks were easily the best team in the world at the time (at least acknowledged to be in New Zealand), but several of the team had mysteriously come down with food poisoning on the morning of the match.
But the Springboks and the whole nation behind them were elated. In fact, they remained elated for the whole month I was there. And - being one of the vanquished - everybody wanted to re-live the experience with me. The charismatic Springbok captain, Francois Pienaar, and the even more charismatic PM, Nelson Mandela, had made it a truly unifying experience that helped immeasurably to lift South Africa out of the apartheid era. On balance, perhaps that gain was a little more important than our loss ….
One of the first things Greg and I did was to start looking at how the UV at Lauder compared with other places. That work began before he moved permanently to Lauder, when we used satellite ozone data to show that there’s nothing special about ozone at New Zealand’s longitude (but there were hints of a downward trend in ozone that would lead to an upward trend in calculated UV).
We then went on to demonstrate the variability of UV in the New Zealand region. Early in the piece we showed that UV measured at Leigh in the north of the country was significantly greater than at Lauder, in the south. Greg hit on a novel way to display calculated variabilities in UV. He produced these eye-catching colour contour plots for a paper in NIWA’s Water & Atmosphere way back in 1996. They compare the calculated daily and seasonal variations in sun-burning UV at the two sites, and summarised the picture very nicely indeed.
He called them Madonna plots. Coming from an earlier generation, I would have perhaps called them Sabrina plots.[1] But of course no such frivolities are allowed nowadays.
We took three take-home messages from Greg’s plots:
1. The UVI is strongly peaked near the midday period, with about half of the daily UV dose arriving within 1.5 hours of solar noon.
2. There’s a huge seasonal variation in UVI, with winter values being
only 10 percent of summer values in the south.
3. The UVI is higher in the north, especially in winter when it’s twice that
in the south.
It’s mainly due to Greg’s initiative that no country has better information about its UV levels than New Zealand. That was through the development of a tool we call the “UV Atlas”, which was designed to make UV data available for epidemiological studies like finding relationships between UV exposure and skin cancer. Because it includes several possible output weightings, it’s also useful in many other ways, including assessment of the effects of UV on other human health issues, plant damage, and damage to materials such as plastics and paints. The UV Atlas uses data from a network of about 100 instruments distributed around the country to measure incoming solar energy. These are used, along with models, to calculate the effects of cloud and aerosols. Greg then found and parameterized the relationship between cloud effects at those longer wavelengths compared with their effects at UV wavelengths. We then used ozone measurements – mainly from satellites - to calculate the clear-sky UV and applied that cloud correction. As a result, we have UV data at 1-hour intervals from about 100 sites, going back to the 1960s in some cases.
It’s worth thinking a bit more about the different cloud effects between UV and visible wavelengths. Any photographer worth their salt can tell you that if you want to produce a dramatic skyscape, you should filter out the blue end of the spectrum. That’s because you want a sharp contrast between the light reflected from the brighter cloud compared with the darker sky. That contrast is largest at the red end of the spectrum.
That contrast between cloud and sky also explains why the highest amounts of radiation occur on partly cloudy days, rather than cloudless days. If the Sun isn’t obscured by clouds, the radiation can exceed the clear-sky value by more than 20 percent. But, of course, when the cloud obscures the Sun the total energy is less than for clear skies.
The wavelength (or colour) dependence in the contrast between cloud and sky occurs because the light-scattering efficiency from air molecules increases rapidly as you move from the red to the blue end of the spectrum. It’s called “Rayleigh” scattering (named after its discoverer). The wavelength dependence is so large that when you go from red light (~670 nm) to blue light (~470 nm), the scattering efficiency increases by a factor of 4. That’s why the sky is blue (in case you ever wondered). You might ask then, why is the sky not violet? It’s true that violet light (near 400 nm) is scattered more, but we don’t see it as strongly as blue light because at those wavelengths our eye is less sensitive, and also because the output from the Sun is smaller at that wavelength.
There’s also an altitude dependence. As you climb to higher altitudes, there’s less overhead air, so the sky becomes darker, as you may have noticed when you look up from the window of a jet aircraft at cruise altitude. Without that scattering, more of the Sun’s energy arrives in the direct beam. Outside the Earth’s atmosphere, the overhead view seen by an astronaut is completely dark. All the Sun’s energy gets to that point in the direct beam.
The increase in scattering efficiency continues at shorter UV wavelengths too. By 300 nm it has increased by another factor of 5 compared with blue light. The upshot is that while most of the Sun’s energy – including the sunlight we see - is in the direct beam, at the shorter UV-B wavelengths most is in the diffuse component of scattered sunlight. If your eyes were sensitive to UV-B instead of visible radiation, it would be like living in a perpetual fog. Objects more than a few kilometres away would be swallowed up in the foggy gloom. No magnificent horizon vistas.
There’s another implication too, that might be important for health. Shadows aren’t nearly as deep and distinct at UV-B wavelengths, just as for visible light when a thin veil of high cloud blocks the Sun. If you look at the edge of a shadow on the ground as a cloud begins to block the sun, you’ll see that the shaded area brightens as the unshaded area darkens. That means that when you seek shade under a tree, the protection from UV-B you’re getting is nowhere near as much as you might expect from your visual perception. By blocking the direct sunlight, the light you see is less than 10 percent of that in unobscured sunlight, while the UV component may still be 50 percent or more of the clear-sky value.
Our team was bolstered in 1995 by the arrival of Brian Connor, from NASA Langley. Brian was already an experienced ozone research scientist. He and Greg were co-authors of our 1999 Science paper which showed that in the previous 20 years, summertime ozone had decreased by nearly 10 percent at Lauder. If we’d been measuring sun burning UV over that entire period, we would have seen an increase greater than 10 percent. But we’d been measuring it for less than 10 years, so the increases we’d seen were closer to 5 percent. Brian and his PhD student Jelena Ajtic[2] went on to show that only half the ozone depletion seen at Lauder was attributable to the export of ozone-poor air from Antarctica, so ozone losses in populated areas outside that region were starting to become important. Any continuation of that would be troubling because of the increased skin-damaging UV. Lives were potentially at risk.
Greg noted (with tongue firmly in cheek) that if Lauder’s ozone depletion rate over the previous 20 years were to continue unchanged into the future, there would be no ozone left by 2250. That’s still 230 years from now, long after I’d be personally concerned. And, luckily for future generations, we both knew that it couldn’t really happen, because of ozone’s “self-healing” effect. Some ozone will always be regenerated as long as there’s oxygen in the atmosphere and UV from sunlight available to break those oxygen molecules apart. But that didn’t mean that ozone couldn’t be depleted enough to cause health risks. I later joked with Greg that I could happily retire only after we had safely solved the ozone depletion problem. My remark turned out to be eerily prophetic.
Greg soon rose through the ranks at NIWA and in time he became my boss. Then he had a row with management and departed to start his own company.
About four years before he left, we co-authored a paper comparing peak sun burning UV between Lauder and rural USA at similar latitudes. We made use of data from a network of about 35 instruments maintained by the United States Department of Agriculture (USDA). All sites except one were in the USA or Canada. But, because of our expertise in the field, they had wanted one to be located at Lauder alongside our state-of-the-art spectrometers.
Our paper reported that the peak sunburning UV in New Zealand was about 40 percent greater than at corresponding latitudes in the USA. Unlike the earlier comparisons with the more polluted sites in Europe, this difference was much harder to explain. Only 15 percent was due to differences in ozone and seasonal differences in Earth-Sun separation, leaving a whopping 25 percent to be explained by aerosol effects.
But model calculations of the time suggested that their effects should be small at those rural locations. Our study showed that wasn’t the case and that their effects were much larger in the UV-B region than previously thought. We now know that they can absorb radiation, as well as just reflect it (or scatter it) at these wavelengths. Previously it had been assumed that they would reflect it, without loss, as most aerosols do at visible wavelengths. So it wasn’t just ozone that mattered. The important roles of clouds and aerosols meant that future UV levels would also be influenced by climate change.
The paper was one of our most cited. Its main conclusion - that our peak UV was 40 percent greater than at similar US latitudes - is even quite widely known by the New Zealand public. I often hear the result quoted (or misquoted – they usually leave out the word ‘peak’) by sunscreen suppliers exhorting me to buy their products.
The wider public uptake may also have something to do with my son Hamish. He was halfway through a master’s degree in journalism in Canada and was back in New Zealand for a mid-course internship (and a holiday with us) when the paper was published on February7, 2006. That was just the 2nd day of his internship at Wellington’s Dominion Post, which is one of New Zealand’s leading newspapers. He must have had a sympathetic editor because his write-up of our work made the front-page news.
[1] Sabrina (Norma Ann Sykes) was a glamour model in the 1950s.
[2] Jelena is from Serbia and I must thank her for pointing out an error (now corrected) in chapter 1 where I had attributed Milankovitch’s nationality as Russian instead of Serbian. They’re very proud of him there and for them my error was nearly as bad as it would be for us if somebody attributed New Zealand’s Ernest Rutherford to Australia (though there are plenty of other famous Serbian scientists, including Nikola Tesla).
Next week. Running with the hares and hunting with the hounds ...