Real Climate Records

THE results of climatic studies by an Australian physicist, Mr. E. L. Deacon of the Section of

Meteorological Physics, C.S.I.R.O., Melbourne, support the view, widely held overseas, that world weather conditions are changing.

Australian summers, Mr. Deacon says, are becoming wetter and somewhat cooler, and the winters drier than they were around about the turn of the century.

These conclusions are based on an investigation of temperature, rainfall, and air pressure trends in Australia during two 30-year periods, from 1881 to 1910 and from 1911 to 1940.

Mr. Deacon admits that these conclusions will need to be confirmed by a longer series of ob-

servations, but he points out that the apparent changes here are of a similar basic character to those detected in the northern hemisphere, and he suggests that they are due to identical causes.

The immediate cause he considers to be an increase in what physical circles term “meridional

interchange”-that is, an increase in the movement of great masses of air in a northerly and southerly direction, from the poles to the equator, and vice versa.

Such movement of the air is brought about by the difference in temperature between the

equatorial and polar regions, which creates differential air pressures.

At the equator the heated air rises, while, at the poles, the cold air sinks to the ground. There

is, therefore, less air and so less pressure in the upper atmosphere at the poles than at the equator.

The upper air, which is warm, then gravitates towards the poles and a corresponding draught of colder air moves along the earth’s surface from the poles towards the equator.

This massive interchange of air, apart from the amount of heat put out by the sun, is a major factor conditioning the climate of various parts of the world.

The thesis advanced by a majority of climatologists overseas though not necessarily accepted by all is that meridional interchange has been increasing over the last half century or so.

In seeking to explain this, scientific opinion tends to the belief that the output of heat from

the sun is a variable, and that it is increasing to a measurable extent.

An American astro-physicist, Dr. L. B. Aldrich, of the Smithsonian Institute, claims to have measured an increase of one quarter of one per cent, in the sun’s radiation over the last 20

years.

Mr. Deacon points out, in referring to climatic changes observed in the northern hemisphere, that “glaciological studies have demonstrated a notable retreat and thinning of glaciers in many areas, trends which have in most cases accelerated since about the beginning of the century.”

The climatological evidence points to an increased transport of heat into high latitudes by the

general circulation of the atmosphere during this period, with an appreciable increase particularly in the mean winter temperatures over large areas, mainly in high latitudes.

“A similar study for the southern hemisphere,” he adds, “is handicapped by lack of data for

high latitudes and by the shorter period of instrumental observations.”

Mr. Deacon began his work by searching for climatic trends in Australia which might have re-

sulted from a change in the general circulation of the globe. His guiding idea was that such change would probably most strongly affect the summer climate and that, more particularly, it would be reflected in the mean daily maximum temperatures of inland towns.

Lower Mean Figures He studied the mean daily maximum temperatures, in summertime, of 14 inland towns which had sufficiently complete temperature records extending back to 1881. His report says:

“All these localities show lower mean summer maximum temperatures in the period 1911-1940, and the average fall of 2.5 degrees Fahrenheit is comparable in magnitude to the simultaneous changes in winter temperature in north-west Europe.

The good consistency of the changes suggests the cause to be mainly climatic rather than changing observational technique or exposure.”

Summer maximum temperature falls experienced by the towns included in the survey ranged from 0.5 degrees at Goulburn to 2.3 degrees at Alice Springs and 4.7 degrees at Cooma.

Mr. Deacon has analysed the rainfall records of the Adelaide region in some detail, to illustrate

his proposition that the summer rainfall increases in the second period were not merely due to

one or two exceptionally wet summers, but were part of a long term climatic trend.

Thus, in the period 1881 – 1910, the Adelaide region experienced 17 summers with less than two inches of rain, but only nine summers with that meagre rainfall between 1911 and 1940. Conversely, there were only six summers in which the region registered more than three inches of rain in 1881-1910, but 11 summers with more than three inches in 1911-1940.

In general, the summer rain fail increases over the whole area were greatest in February, mod-

erately large in December, and negligible in January.

“Winter precipitation (June, July, August),” Mr. Deacon adds, “has changed less markedly than that of the summer between the two 30-year periods but the second period was drier over

much of the area, particularly in the interior of South Australia.”

Trends Continue Mr. Deacon considers that the lower maximum summer temperatures experienced during the second of the two 30-year periods may be explained as due to the same factor increased meridional interchange of cold air from the Antarctic with warm air from tropical regions which is seen as the cause of the higher summer rainfall readings.

That, he believes, is so because the presence of cold air would account for an increase in cloud

amount during summertime and, hence, a drop in inland maximum temperatures.

Reviewing the results of his studies of the periods 1881-1910 and 1911-1940 with climatic events of the decade 1941 to 1950.

Mr. Deacon concludes that these rainfall and temperature trends are continuing. In fact, he says, around Adelaide and in western Victoria the last decade had an average summer rainfall nearly half as great again as the period 1881-1910. Summer temperatures, in general, have continued to follow a declining trend.