THE SEASONS

Te Awamutu Courier, Volume 79, Issue 7100, 29 August 1949, Page 8

THE SEASONS

SUMMERS GRADUALLY BECOMING WARMER It’s getting warmer every year—but not much warmer. Accurate temperature r ecords kept since about the middle of the eighteenth century show that northern hemisphere summers have grown three degrees hotter in the last 200 years. It will not be possible to decide whether New Zealand summers are becoming warmer till about 2049, however. “To do that,” said Mr N. G. Rqbertson, officer in charge of the ciimateological section at the Meterological Office, “one would have to have the record of a thermometer screened and mounted in one spot for 100 years, preferably with the conditions around it remaining the same in all directions for 10 miles. A series of readings taken under those conditions is not available.” In the United States the growth of a city has been found sufficient ts increase the mean temperature of its environs by a degree or so. Wellington temperature records went back only to 1862. Because the recording instruments had been housed in many parts of the city in the intervening years, height corrections had to be made before the city’s mean temperature could be compared. Temperatures fell about three degrees for every 1000 feet of altitude That European summers were becoming warmer was revealed by a paper on temperature trends in Lancashire from 1753 to 1945 and by records kept at Stockholm since 1760. The Stockholm records showed a rise of two degrees in summer temperatures and those of Lancashire a rise of three degrees. No alteration was shown in the cold of European winters, however. The greatest difficulty in determining climatic trends was in gaining an accurate record of air temperatures, said Mr Robertson. It was not an easy quantity to measure. Standard instruments had to be used to avoid errors in thermometers. To ensure they did measure -temperature accurately they had to be sheltered from direct radiation from the sun and from surrounding buildings. At the same time there had to be a free circulation of air over the instruments. An increase of only a few tenths of a degree in an area’s mean temperature might be sufficient to cause all sorts of significant physical changes as instanced by retreating glaciers. For the last few years New Zealand glaciers had been lengthening, however. This was not entirely due to polder temperatures as the yearly fall of rain and snow also affected the increase.