Is Climate Changing?

New Zealand Mail, Issue 852, 29 June 1888, Page 9

Is Climate Changing?

(Robert H. Scott, in ‘ Longman’s Magazine.)

As regards the actual change of mean temperature, we possess at least for Vienna and Paris, records extending back for more than a century. The change of temperature which these show is very slight indeed, not extending to much more than a degree or so ; an amount which can easily be accounted for by differences in the actual instruments or in the mode of taking the observations. As regards London a recent paper by Mr H. S. Eaton, ‘On the Mean Temperature of Greenwich from 1811 to 1856,’ contains the following figures for four eleven-year periods :

Hera there is no evidence of a regular decrease of temperature. Accordingly we must consider the fact of any serious deterioration of our climate, as regards the mean temperature, is not established. It may, however, be alleged that the change does not manifest itself in a lowering of the mean temperature, but in a more freqnent recurrence of exceptionally odd seasons. Now, as regards this point, Dr. W. Koppen of Hamburgh lias set himself to ascertain if any periodicity is discoverable in the recurrence of characteristic weather. He selected exceptionally severe winters, as being phenomena certain to be recorded, owing to the widespread severe distress which their occurrence was certain to entail. The final outcome of his papers ‘ On Protracted Periods of Weather ’ is the following :— ‘ The main feature of the entire investigation has been to prove that for certain intervals strongly marked periodical influences make their appearance and then vanish entirely, at times being replaced by others of a totally different oharacter. No law has, as yet, been discovered for these changes, and so the outcome of the inquiry is, on the whole, nega tive.’ It is self-evident that it there had existed any general tendency towards a lower temperatnre, indications of such a serious change mußt have come out in the course of Dr Koppen’s research, which extended back to the year 462 of our era. As regaids our own climate here in London, we know that severe winters have certainly not been experienced more frequently than usual of late years. Within the last ten years we have had three severe winters, which have been

described in the Journal of the Royal Meterological Society in successive papers by Mr W. Marriott and Mr Charles Harding. The former of these gentlemen gives ( rol. vii. p. 146) a table showing the mean temperature of London iu January for each year Binee 1774. From this it appears that the temperature of that month in 1881 was 31‘6 deg., and that the only years in which the January mean temperature had been below the freezing-point were sixiu number—lß79, 31-9 deg.; IS3B, 30-5 deg.; ISI4, 28’5 deg.; 1795,25-5 deg.; 17S0, 30'2 deg.; and 1776, 28’6 deg. Here at. least there is no evidence of progressive deterioration of climate, and January may be said to be a fair test month for the quality of a winter. Mr Harding gives (vol. xii. p. 235) a table showing the total number of days of, continuous frost at Greenwich during the whole winter for fortytwo years, from 1845-86. Iu the winter of 18S5-S6 there were twenty-eight such days (from February 19 to March 18). The instances of intervals exceeding twenty days were—lß79-80, twenty-two days ; IS7B-79, twenty-one days ; 1857-58, twenty-four days ; and 1554-55, twenty-one days. Here, again, there is no evidence of progressive increase iu the duration of frost. As far, therefore, as the records of temperature go we can only conclude that M. Reynaud’s thesis is not proved, and that any deterioration of our climate is quite inappreciable. Let us now take another element. As regards the rainfall it is constantly stated that infallible periodicities have betn discovered, but the more catefully the records are studied the more certainly are all suah statement's discredited. In Symons’ ‘British Rainfall’ for 18S6 a plate will be found giving the average fall over the United Kingdom for the last 160 years , from 1726 to ISB6, which affords ample material for testing any of these theories. In the first instance, during the period from 1880 to 1883, it was constantly remarked that the climate of England had become so wet that it was useless to cultivate cereals, and that all land should be laid down in grass. In fact, in 1883 we had the last of a series of nine successive wet years —of years jn which the fall had been above the average. Such a series of wet years had never before been experienced during the entire period of 160 years shown in Mr Symons’ plate. If, however, we examine the record, we see that during the thirteen years 1738-50, conditions the exact opposite to the foregoing had prevailed—the fall was markedly below the average. Such a persistent drought as this has never been since on record. The drought .was in reality more prolonged than the above statement would show, for if we except the single year 1751, which was wet; the drought lasted for a quarter of a century from 1738 to 1762. We oau easily imagine investigators about the year 1760 announcing that the proverbial dampness of the British climate had disappeared and for ever ! Such ideas would, however, be rudely upset by the figure for the year 1763, whioh was considerably higher than the average, and this year was succeeded five years later by another much wetter year. Suoh a period of, drought as has been mentioned has never since recurred. It will, therefore, be seen that we have the two extremes of long-continued drought and long-continued wet weather occurring at an interval of about 140 years from each other, and each set in without the slightest apparent indication of its approach. Announcements are repeatedly made that wet years follow each other at intervals of ten, eleven, or twelve years. As regards the twelve year period, it is said that the years in this century of which the numbers are multiples of twelve are wet. This statement is supported by the years 1824, 1836, 1848, 1860, and 1872 ; but not by the years 1800, 1812, and 1884. Accordingly the rule is not to be trusted implicitly. In the last century it failed signally, for only two of the series. 1728 and 1776, were wet ; while 1740, 1752, and 1788 werediy, and the fall for 1764 was exactly the average amount. Let us now examine the ten-year period. It is often asserted that years of which the number ends in four ar6 dry. This is apparently reasonably correct for the present century, for 1824 is the only wet year coming under the category. In the last century the rule did not hold quite so true, for the years 1734, 1774, and 1794 were all wet. All such alleged periodicities, however, throw no light on the question of whether the rainfall of the British Isles is decreasing or the contrary, and it is hopeless to look for evidence before the year 1726, with which Mr Symons’ carefully compiled diagram commences. It will therefore appear that, whether we look to temperature or to rainfall, the finding on the whole inquiry as to whether climate is changing or not is most decidedly ‘not proven.’

Period Mean temperature 1812-1822 .. 48-95 1823-1833 49.55 1832-1844 48.84 1845-1855 49.25