Is Our Climate CHANGING?

New Zealand Listener, Volume 37, Issue 935, 12 July 1957, Page 4

Is Our Climate

CHANGING?

F there is one point on which people agree when they discuss the world’s commonest topic, it is that the climate was very different when they were young. It is only when they begin to explain why it was different that disagreement arises. And whether their arguments are for wetter, warmer, drier, or colder-or perhaps all of these in turn, every time a report comes of record rainfall or sunshine ("greatest since 1910") they feel their case is proved. Twenty years ago old timers would passionately claim that "It’s all this radio that’s doing it."-These days, impressed by vastly greater technology and not sure of anything any more, it is more likely to be: "I bet it’s the Bomb"-said jokingly, but with a discernible undercurrent of seriousness all the same. Several years ago the Press in England put the Bomb question to the British Atomic Research chief, Sir William: Penney. "Could it be that which is responsible for the very bad summer?" they asked. "No, gentlemen," he replied, "it’s ‘not the atom bomb, it’s television." Seeking some definite answer on this perennial question of changing climate, The Listener decided to climb to the Meteorological Office on Kelburn Hill behind Wellington city, and consult the experts. In the Research Section we met the head of the Section, Dr J. F. Gabites and a Senior Meteorological’ Officer, Dr J. F. de Lisle. Our first question touched on a recent report in the Press, in which an Australian C.S.LR.O. meteorologist had said that Australian weather was slowly changing, owing to some change in the high pressure belt that, by and large, controlled the weather over the Commonwealth. He had added that the H-bomb had nothing to do with this

change. What, we wanted to know, was the significance of this report? "We thought there would be repercussions from that," said Dr Gabites wryly. He explained that it was hard to tell what the scientist was getting at from reading such a bald report. This particular scientist was well known for

his research work into long-term climatic trends, and the- report may refer to some later and as yet unreported development in his studies. Well, then, we asked, was there any ground for believing that New Zealand’s climate was changingthat the seasons were not as clearly

defined as they used to be? "People," said Dr Gabites, "talk of a wet season or a dry season; and while this may be true of their particular area, it may not be true for the rest of the country at all. January this year, for instance, was rather dry, yet some parts of the country had more than the normal rain." Normal rainfall, he went on, was Ccetermined on a 30-year average, and though there were broad patterns, month by month and _ season by season the location of storms and settled weather varied. Last May, South Eastern Australia had very marked anti-cyclonic conditions, and a resulting drought, while New Zealand had a series of repeated depressions coming from the south-west. These fast moving depressions reached their greatest development east of the country, and gave a large percentage of rain to the south-eastern part of Otago and Southland. For Invercargill, with 8.60 inches, it was the wettest May in over 50 years of record. Over most of the country-the exceptions being North-

land, Gisborne and Hawke’s Bay-rain-fall was above normal. The only place to have much more than normal sunshine was Gisborne. "Now take May, 1956, as a contrast. Whangarei had had its wettest month for 50 years in April and May was even wetter. Gisborne and other eastern districts

had less sunshine than they had ever previously had in any month. And there was a tornado in Te Awamutu. This May the tornadoes were at Kaitaia and Lower Hutt. "Also in contrast to May this year, the southeastern seaboard of Australia last year would have plenty of rain because of a deep depression sitting in the Western Tasman, (See weather maps, page 4). "So you. see," Dr Gabites concluded, "the fluctuations from month to month, and season to season — especially the larger fluctuations — obscure any slow climatic changes that may be going on. It is really these larger fluctuations, and the variability from season to season that impress the man in the street, and that he particularly . notices. Put even simpler, it’s today’s clouds and tomorrow’s tain that are important." Dr de Lisle, contributing to the picture, explained that it was these large fluctuations that had to be taken away and ignored in any research into general trends in our records of rainfall. He had done this recently in a survey of West Coast rainfall, a survey which had some interesting results. Two research methods were used in this survey, Dr de Lisle explained,

both methods being ways of looking at the record through eliminating the "larger fluctuations" mentioned earlier. In the first, by drawing what are called "ten-year moving averages," the year by year changes disappear and only the broad features remain. The second technique is an analysis of frequency. As illustrated in the diagram on this page, the short period waves or oscillations, at the top, show no particular trend, but in the graph at the bottom, where all the short period waves are cut out, a longer wave or trend shows up. Both these methods, said Dr de Lisle, could be compared to picking out the main theme in a piece of music scored for a large orchestra. "Both methods showed a 20 to 30year trend in the record of spring rain-fall-a general decrease from about 1912. But you must remember this occurred only in a particular place at one particular period. This particular climatic trend is very minor-and completely obscured for the ordinary man by the far larger yearly fluctuations." One could only guess at the reason for the occurrence of this trend, said Dr de Lisle. There were a number of possible explanations. "This particular change could be caused by a shifting southward of the westerly wind belt-but why this latter change would occur is another problem again. We have only put the question one stage further forward." Looking at the charts on Dr Gabites’s desk, we wondered what the "stage further forward" meant. The West Coasteven New Zealand-looked very small in half a hemisphere of swirling and waving wind patterns. Was there any other evidence of climatic trends? What about temperatures?

"In New Zealand we haven’t got good enough records of temperature to analyse," said Dr Gabites. "Most records have suffered from the changing of site of the observing station. In Wellington the site has been changed three or four times, being at different times on low or high ground, which in itself is sufficient to vary readings. "Cities have also grown up around observing sites. If even a tree growing up or being cut down can vary records, you can imagine how a city, with its buildings absorbing and releasing heat in various ways can ruin them." : Though they had no good evidence at present in New Zealand of significant temperature changes, said Dr Gabites, it was always possible that some might be uncovered in the future. Our last question to Dr Gabites was on the work being done during the International Geophysical Year which, for metedrologists, began on June 20. "We hope to gain from 1GY in two ways," he said. "In the very broad theoretical field, and in the more immediately practical." During IGY information would be available from areas that were previously blank, and also from areas that would otherwise be supplying only limited observations. Such information would help to give the broader knowledge which was so essential to longterm forecasting. Dr Gabites touched a chart. "It is not very helpful," he said, "to know that at this point there is a disturbance approaching, if we don’t know that there is a big area of anti-cyclonic activity developing here to block its advance, One must have the complete picture if possible." 5:

The benefit in the theoretical field, explained Dr Gabites, could well come from the intensive study of what, in the final analysis, was the beginning and end of all our weather-the sun. "The sun drives the atmosphere, for the wind systems are ultimately due to the heating from the sun. There have been some investigations in the tropical Pacific which _ suggest that events on the sun, like solar ares, may have some effect on the temperature conditions in the high atmosphere and ultimately on the wind circulation. Besides investigating this, the IGY scientists will also make a general study of the distribution of the sun’s rays and on the fate of the outgoing radiation from the earth and atmosphere. "Through this work we may learn something fundamental about the nature of weather and climate." In the meantime, there is apparently little evidence of major changes in New Zealand’s climate and the weather seems, to the average man-in-goloshes, as erratic as ever,