evidence: The only reliable data I know of on rate of warming comes from Greenland ice core data that records Arctic warming during the transition from the last Ice Age (i.e., the beginning of the Holocene Interglacial, which began about 11,500 years ago). This warming was extremely rapid by any measure – about 5-100C of that warming took place within 30 years or less (Alley 2000). As far as I know, this is the only good data we have on the rate of warming over any period of time, during any transition into an Interglacial period, that is short enough to compare to current global warming rates since 1950 that are blamed by some people on human emissions of carbon dioxide but that others point out is well within natural variation. [...] "Neither the rate nor the magnitude of the reported late twentieth century surface warming (1979-2000) lay outside the range of normal natural variability, nor were they in any way unusual compared to earlier episodes in Earth’s climatic history." .