Climate Change in Australia - Pre-instrumental Climate Change

Pre-instrumental Climate Change

Paleoclimatic records indicate that during glacial maxima Australia was extremely arid, with plant pollen fossils showing deserts extending as far as northern Tasmania and a vast area of less than 2 percent vegetation cover over all of South Australia and adjacent regions of other states. Forest cover was largely limited to sheltered areas of the east coast and the extreme southwest of Western Australia.

During these glacial maxima the climate was also much colder and windier than today. Minimum temperatures in winter in the centre of the continent were as much as 9°C (16°F) lower than they are today. Hydrological evidence for dryness during glacial maxima can also be seen at major lakes in Victoria's Western District, which dried up between around 20,000 and 15,000 years ago and re-filled from around 12,000 years ago.

As one moves into the Holocene, evidence for climate change declines. During the early Holocene, there is evidence from Lake Frome in South Australia and Lake Woods near Tennant Creek that the climate between 8,000 and 9,500 years ago and again from 7,000 to 4,200 years ago was considerably wetter than over the period of instrumental recording since about 1885. The research that gave these records also suggested that the rainfall flooding Frome was definitely summer-dominant rainfall because of pollen counts from grass species. Other sources suggest that the Southern Oscillation may have been weaker during the early Holocene and rainfall over northern Australia less variable as well as higher. The onset of modern conditions with periodic wet season failure is dated ar around 4,000 years before the present.

In southern Victoria, there is evidence for generally wet conditions except for a much drier spell between about 3,000 and 2,100 years before the present, when it is believed Lake Corangamite fell to levels well below those observed between European settlement and the 1990s. After this dry period, Western District lakes returned to their previous levels fairly quickly and by 1800 they were at their highest levels in the forty thousand years of record available.

Elsewhere, data for most of the Holocene are deficient, largely because methods used elsewhere to determine past climates (like tree-ring data) cannot be used in Australia owing to the character of its soils and climate. Recently, however, coral cores have been used to examine rainfall over those areas of Queensland draining to the Great Barrier Reef. The results do not provide conclusive evidence of man-made climate change, but do suggest the following:

1. There has been a marked increase in the frequency of very wet years in Queensland since the end of the Little Ice Age, a theory supported by there being no evidence for any large Lake Eyre filling during the LIA.
2. The dry era of the 1920s and 1930s may well have been the driest period in Australia over the past four centuries.

A similar study, not yet published, is planned for coral reefs in Western Australia.

There exist records of floods in a number of rivers, such as the Hawkesbury, from the time of first settlement. These suggest that, for the period beginning with the first European settlement, the first thirty-five years or so were wet and were followed by a much drier period up to the mid-1860s, when usable instrumental records start.