Weathered glacial deposits outside limits of the last glaciation show that the New Guinea mountains were covered by glacier systems before Oxygen Isotope Stage 5. KAr dates from interbedded volcanic materials suggest that earlier glaciations may have occurred at ca. 300 ka BP and at ca. 700 ka BP. This implies that the still tectonically active island was high enough in the Early and Mid Quaternary to support mountain ice caps. Glacial deposits older than a radiocarbon age of 30 ka BP suggest that New Guinea developed glaciers in the early part of the last glaciation, most probably during Isotope Stage 4. Following interstadial conditions radiocarbon dated to >31 ka BP and >41 ka BP, the last glaciation is said to have culminated during the interval 18-15 ka BP, but the moraines of this stage are not closely bracketed with radiocarbon dating. Estimates of Equilibrium Line Altitude (ELA) depression are 1000-1100 m, implying a lowering of mean annual temperature by at least 6-7°C (possibly more, as precipitation also decreased). Radiocarbon dates from basal peat within the moraine limits show that glaciers receded by 13 ka BP and that New Guinea may have been wholly ice free by 7 ka BP. A small-scale advance at 121 ka BP was a response to either increased precipitation as global sea level rose and covered dry shelf areas around New Guinea, or to late-glacial global cooling. Glaciers developed again during an interval of Neoglacial cooling beginning at ca. 5 ka BP. At least four significant readvances occurred during the last 3.5 ka, radiocarbon dated to the intervals 3.5-2.9 ka BP, 2.5-1.5 ka BP (two advances) and within the last 1.5 ka BP. The Little Ice Age ended ca. 120-150 years ago and continuous glacier retreat has occurred to the present day.