forests and woodlands. After around 10,000 years of stable climatic conditions, temperatures began cooling and winds became stronger, leading to the beginning of an ice-age. During the glacial maximum, 25,000 to 15,000 years ago, the sea level was some below its present level, with the coastline extending further to the north-west. Australia was connected to New Guinea, and the Kimberley was separated from southeast Asia (Wallacea) by a strait approximately wide. Rainfall decreased by 40% to 50% depending on region, while the lower levels (half pre-industrial levels) meant that vegetation required twice as much water to photosynthesize. The Kimberley region, including the adjacent exposed continental Sahul Shelf, was covered by vast grasslands, while woodlands and semi-arid scrub covered the shelf joining New Guinea to Australia. Southeast of the Kimberley, from the Gulf of Carpentaria to northern Tasmania the land, including the western and southern margins of the now exposed continental shelves, was covered by extreme deserts and sand dunes. It is believed that no more than 15% of Australia supported trees of any kind. While some tree cover remained in the southeast of Australia, the vegetation of the wetter coastal areas in this region was semi-arid savannah. Tasmania was covered primarily by cold steppe and alpine grasslands, with snow pines at lower altitudes. There is evidence that there may have been a significant reduction in Australian Aboriginal populations during this time. It appears there were scattered "refugia" in which the modern vegetation types and human populations were able to survive. With the end of the ice-age, the Kimberley region settled into a tropical monsoon climate until a major El Niño–Southern Oscillation event in the mid Holocene caused the Australian summer monsoon rains to weaken or fail for some 1,500 years. The discontinuity in artistic styles between the earlier Gwion Gwion and the current Wandjina has been attributed to the severe drought phase that followed the collapse of the wet season in 5,500 BP. The Gwion Gwion style art ended around this time, possibly within 500 years. The emergence of Wandjina art depicting cloud and rain spirits 3,800 to 4,000 years ago coincides with the end of the "mega-drought" and a return of the rain which gave the region its current climate. The research paper's lead author, Hamish McGowan, suggests further investigation into the resulting cultural collapse and the possibility that another ethnic group supplanted the Gwion Gwion artists. The chair