麻豆传媒

Joe Farman had only ever published a handful of research papers. He was one of the foot soldiers of science, running instruments monitoring the atmosphere above the UK鈥檚 Halley Bay research base in Antarctica. But one of his rare excursions into print is among the most famous by an environmental researcher. In October 1983, Farman discovered that a huge hole had opened up in the ozone layer over Antarctica 鈥� and that it was man-made. , they caused a sensation 鈥� and major embarrassment at NASA. For while NASA鈥檚 satellites had been monitoring ozone levels around the world 24/7, Farman had found the hole with an ageing instrument wrapped in a quilt. Twenty-five years on, NASA has challenged the accepted version of events. So what really happened?

IN THE early 1980s, scientists thought they understood the ozone layer 鈥� and they thought its future was secure. Fears that CFCs and other synthetic chemicals might be eating into the ozone layer seemed unfounded. In 1984, the US National Research Council reported that rates of ozone loss were less than anticipated 鈥� fractions of 1 per cent. 鈥淭he ozone layer isn鈥檛 vanishing after all,鈥� proclaimed The Wall Street Journal that year. Many environmental groups seemed to agree and dropped the issue.

Enter Joe Farman, chief atmosphere-watcher at the British Antarctic Survey (BAS). While others thought the panic over CFCs was over, he was increasingly alarmed by data coming from one of his prize instruments. His 25-year-old Dobsonmeter calculated the thickness of the ozone layer by measuring ultraviolet radiation penetrating the atmosphere and it showed that ozone levels had dipped sharply for several weeks in October 1982. Then, in October 1983, says Farman, 鈥渋t just went haywire; the levels really fell away鈥�. Half the ozone layer had vanished.

Fearing his ageing Dobsonmeter might be on the blink, Farman sent out a replacement. But by October 1984, the new one was showing an even deeper hole. When Farman鈥檚 findings finally appeared five months later, they caused a sensation, especially Farman鈥檚 suggestion that the hole was not natural but the result of ozone-destroying reactions triggered by CFCs in the stratosphere.

The following year, a research plane flew through the hole and detected the reactions Farman predicted were taking place on the surface of frozen particles in stratospheric clouds over the South Pole. This discovery led directly to the tough new rules on CFCs and other ozone-eating chemicals agreed at Montreal in 1987 鈥� the Montreal protocol.

Farman鈥檚 success was the result of brilliant intuition and dogged research. He had been quietly measuring the ozone above Halley Bay since he first took the Dobsonmeter south during the International Geophysical Year in 1957. Farman鈥檚 triumph was a significant blow for NASA, though. With satellite instruments monitoring ozone levels round the world 24/7 and archiving 140,000 readings a day on magnetic tape back at NASA HQ, why hadn鈥檛 its researchers spotted the hole?

In a radio interview a couple of years later, NASA鈥檚 Richard Stolarski explained that although NASA鈥檚 satellite monitors revealed very low ozone levels across Antarctica, software analysing the data dumped the low readings as obviously false. For years, that was the accepted version of events. Today, however, . Richard McPeters, one of NASA鈥檚 ozone scientists back in the 1980s and still on the team, gives his account of what happened on NASA鈥檚 website. 鈥淚t makes a great story to talk about how NASA 鈥榤issed鈥� the ozone hole, but it isn鈥檛 quite true. In 1984, before publication of the Farman paper, we noticed a sudden increase in low values from October 1983. We had decided that the values were real and submitted a paper the following summer when Joe鈥檚 paper came out, showing the same thing.鈥�

鈥淣ASA鈥檚 software dumped the low ozone readings as false鈥�

The implication is clear: Farman may have published first, but NASA knew what was going on all along. 鈥淲e were right behind him,鈥� McPeters told 麻豆传媒. But that is not how the British remember it. 鈥淚t鈥檚 all a long time ago, but I have never heard anyone from NASA who was actually involved claim they knew anything before I pointed it out,鈥� says Farman. 鈥淪ome of the people who came later now say they found the ozone hole first. But it鈥檚 simply not true.鈥�

So what really happened? According to Pawan Bhartia, who was processing the satellite data, strictly speaking NASA is right to say its software didn鈥檛 destroy the data. What it did was 鈥渇lag it up鈥� 鈥� identifying it as unreliable. The computer, he told 麻豆传媒, then substituted 鈥渇ill values鈥� that it thought more likely. The effect was the same: the 鈥渦nreliable鈥� data was buried and the researchers had no reason to think anything was amiss. They might have re-examined the raw data sooner but for a second mishap. NASA had its own Dobsonmeter at the South Pole, which had been recording low ozone levels in 1983. But in what Bhartia calls 鈥渁 clerical error鈥�, the data was misread.

The British say NASA missed another opportunity to spot that something odd was happening above Antarctica when Jonathan Shanklin, Farman鈥檚 colleague at the BAS, wrote to two NASA contacts in late 1983 about the British team鈥檚 startling measurements. 鈥淚 didn鈥檛 receive any reply that indicated that they had even looked at the data we were sending them,鈥� he says. According to Bhartia, the data never reached his team.

It was only in September 1984 that NASA researchers first realised ozone might be disappearing over Antarctica 鈥� a year after its Nimbus satellite recorded the drop in ozone. At a conference in Greece, they heard Japanese researchers report low ozone values from their Antarctic Dobsonmeter. After that, Bhartia recalls, weeks of frantic checks at NASA finally revealed that 鈥渄ata over large areas of Antarctica were being discarded鈥� and that the low ozone readings were 鈥渞eal鈥�.

Now NASA made another error. Extreme meteorology was known to make spring ozone levels over Antarctica extremely variable. 鈥淲e thought the low ozone readings were an intensification of this phenomenon,鈥� says Bhartia. So still no alarm bells. It was only when Farman鈥檚 paper finally appeared in May 1985 that the penny dropped: the ozone hole was not a natural phenomenon. 鈥淔arman was the first person to recognise that what was happening may be related to chlorine chemistry,鈥� says Bhartia.

NASA had only been collecting ozone measurements for five years, so it was understandable that its team took a while to realise the annual ozone thinning was increasing. But Farman, who had been taking measurements since 1957, realised something dramatic was happening, and that it couldn鈥檛 be blamed on the local weather. Finally, and most crucially, he was also the first to imagine the chemistry of what was happening. 鈥淚t was a brilliant analysis, and has turned out to be essentially correct,鈥� says Bhartia.

Without Farman, the truth might not have been discovered for several years or more. But he couldn鈥檛 have done it without his trusty Dobsonmeter, first assembled in a shed outside Oxford more than 50 years earlier by another dogged researcher, .

The odd thing about the Dobsonmeter is that for a quarter-century it was an instrument without much use. It finally came into its own during the International Geophysical Year of 1957, when researchers decided to make global measurements of the ozone layer. They put in an order for around 50 Dobsonmeters with the London instrument maker, R. & J. Beck.

Farman remembers going to Oxford to pick up his machine from Dobson in 1956. 鈥淓ven after 25 years, they hadn鈥檛 completed the instruction manual,鈥� he recalls. 鈥淭hat only arrived the following year.鈥� Farman still has his original copy. For best results, it recommends wrapping a quilt round the instrument to keep it warm.

Only about 120 Dobsonmeters were ever made, of which some 50 remain in use. Each is known by its number. Dobson鈥檚 original, No 1 (far left), is in London鈥檚 Science Museum. Farman made his discoveries with Nos 37 and 51. Probably the oldest still in use is No 8, now 73 years old and sitting on the roof of the Norwegian Polar Institute in Svalbard. Dobson died in 1976, so he never saw his instrument鈥檚 finest hour.

The ozone hole still forms above Antarctica each austral spring. The Montreal protocol and its successors have drastically reduced the ozone-eating compounds reaching the stratosphere, but healing the hole is proving a slow process, says Farman, because the greenhouse effect increases stratospheric cooling by trapping more heat near the Earth鈥檚 surface. So there are no plans to retire the Dobsonmeters yet. And we鈥檇 probably be well advised to keep a few researchers like Farman 鈥� dogged, unspectacular and unfashionable 鈥� just in case.