ABSTRACT
The most general conclusion from the evidence so far examined-by pollen analysis, former lake levels and so on-regarding the moisture history of Australia is that somewhere about 4000 to 2000 or (more likely) 2500 BC there was a turning point. Before that time throughout the Australian region many places were wetter, and more consistently wetter, than they are today and rainfall had been increasing both in the tropical and temperate regions. Since that time there has been a marginally cooling and drying trend, with rather wide fluctuations superposed on it. These are the views of Professor D.Walker of the School of Pacific Studies at the Australian National University, Canberra, stated in 1978. The same turning point seems to be indicated in the other great deserts of the present world, as is apparent from the last chapter. And much the same epoch marks the turning point in the history of prevailing temperatures as registered by the height of the upper tree line in every part of the world where this has been examined, from northern and central Europe and the Yellowstone Park in Northern America to Japan and the mountains of New Guinea, to New Zealand, and the Andes in South America. The same is confirmed by the history of the northern limit of forests and by the glaciers on the mountains in temperate and lower latitudes. Only in parts of northern Canada and northern Greenland, where there was most residual ice still melting in mid post-glacial times, was the climax of warmth delayed significantly-in some areas until 2000 BC or after. Thus, the evidence of a global event is clear: the climax of our interglacial. The moisture maximum in subtropical and tropical latitudes and the temperature maximum shown by the vegetation in middle and higher latitudes, and on the mountains everywhere, must be seen as related aspects of the warmest postglacial time.
