By Andy May
The Holocene Thermal Optimum ended at different times in different parts of the world, but it had ended everywhere by 4,000 BP (BP here means the number of years before 2000) and the world began to cool. The timeline shown in Figure 1 shows the GISP2 Central Greenland ice core temperature proxies in blue and the HadCRUT 4.4 surface temperature estimates for the same area in red.
Figure 1 (click on the figure to download in full resolution)
Major events in human civilization are noted on the graph. If you download the pdf it prints well on 8.5×11 inch paper. This timeline provides more detail for the last 4,000 years than I could fit on my previous timeline to 18,000 years. The principle reference for the ice core study can be seen here. At the top of the graph the Blytt and Sernander climate periods are noted, these periods are based on their studies of Danish peat bogs and the names are still used in the literature.
Of necessity, this post covers the climate and human events in the northern hemisphere. Some of the climatic events described, like the Medieval Warm Period, were worldwide events. But, some may have only occurred in the northern hemisphere. Nearly all of the historical notes are from Professor Wolfgang Behringer’s excellent book A Cultural History of Climate. The book was suggested to me by Dr. Ronan Connolly and I highly recommend it. It was originally published in German in 2007, I read the 2010 English translation by Patrick Camiller. The translation is quite good and the book is very readable, even addicting.