8000 B.C. Such recession has thus occurred in the past due to natural variability, but has been rare in the most recent few millennia.
In the Andes, at the same glacier where the dated plant material was exposed (Quelccaya), melting in the 1980s was strong enough to destroy the geochemical signature of annual layers in the ice beneath (Alley 2006; Thompson et al. 2003, in press). An ice core taken from Quelccaya in the late 1970s showed that such melt had not happened in at least the previous millennium. This strongly suggests anomalous warmth in the late 20th century. The Quelccaya ice cap has existed without interruption for more than 1,000 years. If its present rate of shrinkage continues, it will disappear entirely within a few decades.
Over the last few decades, the floating ice shelves along the Antarctic Peninsula have been disintegrating, following a progressively southward pattern (Vaughan and Doake 1996, Cook et al. 2005). This is primarily a result of higher temperatures inducing surface melt (van den Broeke 2005). Analysis of sediment cores from the seafloor (Domack et al. 2005) beneath one of the largest former shelves (the Larsen B, which disintegrated in the late 1990s) indicates that this ice shelf had persisted throughout the previous 10,000 years, providing further evidence that recent decades have been anomalously warm.