Thanks Wolram, it may be a good idea to review how the western civilisation got to such an idiosyncrasy with so much persuasion. That development went along these lines.
When we study the tell tale proxies of the past, we observe that Earth climate has seemed to changed continuously. Common sense would dictate that those changes would be gradual, as solar energy influx changes and various processes in the atmosphere, the oceans and on the surface of the Earth interact with each other. Only within the past decades researchers seem to have discovered the possibility of abrupt shifts in Earth's climate.
The discovery of glacier remains, seemingly ad random all over the Northern Hemisphere, has lead to the impression that cooling and warming periods have succeeded each other slowly. This behavior has been attributed to variation in the orbit and variations in spin axis orientation of the Earth, known as Milankovitch cycles. However, from the mid twenties century study of sediment cores (proxies) started to developed. It was soon discovered that large changes had occurred in rapid succession and with the development of radiocarbon dating those changes could be pegged at around 10-11,000 years ago. The abundance of pollen of the arctic tundra flower Dryas octopetala pollen in the sediment layers of a lakebed in Sweden of that time, gave this period it’s name, the “Younger Dryas” (The “Older Dryas” being an earlier –brief- period with some of the same pollen evidence). This occurrence together with evidence of glacier growth in that period labeled it as abnormally cold. Furthermore signs of earlier glacier advance and retreats led to the hypothesis that the last ice age has ended with a glacial maximum, followed by a warming period (known as the Bolling Allerod interstadial) But the assumed warming was suddenly interrupted for a brief period, the “Younger Dryas”. Gazing at these sudden changes, climate specialists started to worry about repetition of such events –presumable another bitterly cold spell in the near future. Stephan Schneider was the first to take this to the public in the 1980ies
Then the ice cores of Greenland became available for study. It was revealed that a period of dramatic change in hydrogen and oxygen isotope ratios roughly co dated the Younger Dryas event, given the uncertainties of carbon dating and the more precise dating of ice cores with yearly layer counting. Since isotope ratios are known to be temperature dependent and borehole temperatures, albeit very coarsely, seemed to confirm that, it was concluded that those excursions resembled large temperature changes indeed. Moreover, the air bubbles in the core samples revealed a close correlation of carbon gasses with the isotope excursions, therefore it was concluded that greenhouse gasses seemed to be the cause of those spectacular warming events. Evidently, the climate appeared to have two stable situations, either warm or cold with rapid transitions in between, apparently triggered by changes in greenhouse gas concentrations, apparently interacting with similar extreme stable phases in Thermo-Haline Currents in the oceans. So there was no doubt about the nature of the “Younger Dryas”, bitterly cold, period.
So, with the current rate of increase of greenhouse gasses, gone was the ice age notion, instead a fear for another rapid climate transition was born, these are the roots of global warming thinking, notwithstanding later developments like the Hockeystick.
There are numerous indications nowadays that the “ice age” mechanism in general may be much more complicated than the warming – cooling notion. For instance, changes in aridity have barely been addressed. Furthermore, changes in isotope ratios can have several causes other than warming. It’s conceded that isotope variation in oceanic cores is poorly understood. And adding to that confusion are the complications of carbon dating; inducing rather variable errors due to large variations of radiocarbon concentration in the atmosphere with the time. When the Younger Dryas hypothesis was developed, those (large) errors were unknown yet and even now, after a much clearer understanding and the availability of carbon dating calibration methods, yet many articles emerge with carbon dates not calibrated to calendar ages.
In short an audit of the ice age notion seems essential.
