The last Ice Age in Australia, New Zealand, and Papua New Guinea

The last Glacial Maximum (LGM) occurred between 25-16 thousand years BP. There is strong evidence that humans had occupied Australia 45,000 aBP (1). Thus people lived in Australia through a time when temperatures were about 3 K lower than now, winds were stronger, and the southern half of the continent wetter, especially over higher terrain. Also, the sea was some 130-150 metres lower so that Tasmania was part of the mainland. Small glaciers were present in the Snowy Mountains and the Tasmanian highlands.

Analysis of buried pollen shows that there was a warming by several degrees and also an increase of rainfall from the depth of the last glaciation at 17 ka BP until the start of the Holocene (2). The major glaciers of New Zealand shrank to their minimum lengths shortly after 10,000 BP, while the steppe grassland and open savannah woodland of southeast Australia became replaced by forest.

In Papua New Guinea's Highlands samples of organic matter, dated at 16,000 and 18,000 years BP, show a reduced rate of weathering, which would indicate temperatures 9.7 K and 11.3 K respectively lower than obtain now (3). Also, pollen from this area indicate minimum temperatures some 10 K lower than now, at about 18,000 BP, the time of the last cold phase of the Quaternary Ice Age. A drop of 6 K is suggested by evidence of former ice caps and glaciers on the highest peaks of Papua and Iryan Jaya.

Maximum rainfall in Australia was eventually reached at about 4000 BP in Tasmania and 8000 BP further north, in Queensland. Temperatures were highest, and about the same as today, between 8,000-6,000 BP. But maximum Holocene temperatures in New Zealand (about 2 K warmer than nowadays) occurred about 9000 BP. So the time of greatest warmth was not reached uniformly in the region.

Over 10,000 years humans had to adjust to a climate change whose extent exceeded what is reckoned on in contemplating the future effect of doubling atmospheric carbon dioxide. On the other hand, it is unlikely that post-LGM warming exceeded a rate of 0.1 K/century in Australia, which is but a tenth of current global warming.

1. Williams, M.A.J. 1991. Evolution of the landscape. In C.D.Haynes, M.G. Ridpath and M.A J. Williams (eds) 1991. Monsoonal Australia (Balkema, Rotterdam).
2. Kershaw, A.P. and G.C. Nanson 1993. The last full glacial cycle in the Australian region. Global and Planetary Change, 7, 1-9.
3. Ruxton, B.P. 1999. Former low temperatures and unusual turbulence above an isolated peak in northeast Papua. Paper presented at the 6th National Conference of the Australian Oceanographic & Meteorological Society, Canberra, 8/2/99.