A new article at http://popular-archaeology.com/issue/winter-2017/article/climate-change-… … it has been increasingly shown that population numbers had already crashed prior to the arrival of Europeans. The latter are usually blamed for introducing new diseases of which the locals had no natural resistance (and no doubt this did occur). It is the scale of the drop in numbers that is most problematic. It has also been convenient to blame the Spanish and Portuguese for bringing smallpox to the Americans. Populations crashed most notably in Amazonia and amongst the mound builders on the Ohio and Mississippi river valleys. What caused this to happen? In the one solution to fit all mentalities we are now being told that climate change was responsible – rather than an epidemic. They produce some nice evidence to support their view but you are left wondering if it is as simple as that. Why didn't they up stakes and move elsewhere – to where the grass was greener. Researchers from Indiana University-Purdue University claim to have reconstructed 2100 years of temperature and precipitation data that indicates drought was a game changer.
The evidence is derived from lake sediment cores rather than industrial level climate science – so we can take the core results seriously. These are like tree rings in a way – they can be used to reconstruct phases of wet and arid weather patterns. The researchers think the amount of rainfall affected food production – and the people subsequently disappeared. In fact, they found they started disappearing around 1300AD, which represents a decline in climate in Europe as well. In fact, over here it became extremely wet so much so that crops rotted in the field. It caused famine and population decline amongst the peasants of Europe (and no doubt in the world beyond Europe too). It is not a surprise to find North America (in this instance the Mid West) was similarly affected by the weather at the same point in time. It amounted to a global cooling phase, a drop in average temperatures but instead of heavy and persistent rain the Mid West experienced a paucity of rainfall (it became dry if the lake sediments are reading true). None of this is particularly remarkable as all it means is that a cooler globe caused the jet stream to shift southwards. We've met this situation in central Asia when discussing the expanding and contracting phases of the Caspian and Aral seas. However, was the disappearance of the mound builders solely as a result of dry weather. One can see that colder weather in summer months would affect maize yields (and although modern varieties will grow in cool zones they really do like the warmth of their point of origin in Mexico and central America). It is a moot point. The medieval warm period was probably as warm if not warmer than the 20th century and therefore maize yields in the Mid West would have blossomed. Once cooler weather set in during the late 13th and 14th centuries they would have failed – and this is the point being made by the researchers. However, the weather briefly got warmer – in the 15th century (the so called little medieval warm periods that coincides with Tudor England). It so happens that in the 15th century the Spanish and the Portuguese were staking out the New World, establishing colonies and taking advantage of a drastic decline in population amongst the natives. The moot point here is what caused the population decline as it can't all be put down to climate change. People adapt and live off game or other crops – or are they saying the Mound Builders could not survive if their beans, squash and maize would not grow in a cool environment.
It is also noticeable that they ignore a paper last year that claimed a massive Mississippi flood may have washed away the fields of the Mound Builders – and they produced physical evidence to show it had occurred. There is also the possibility that the plague (which struck the Old World in the 14th century, not too long after 1300AD), may have been carried across to America in the atmosphere – somewhat like modern Bird Flu. Now that would have caused a distinct drop in population numbers – but you have to have the burials of plague victims to put this idea forward seriously. For the moment, climate change (and the big flood) are enough to account for the decline of the Mound Builders.
Note … the lake sediments were cored from Martin Lake in NE Indiana. This appears to be in Lagrange County, in the vicinity of Wolcotwille, virtually at the same latitude as Chicago and Toledo. Indiana abuts Ohio and in the south reaches as deep into the Mid West as Louisville (the opposite side of the river). It is a long county and a mainly rural farming area, it would seem, but sediment cores in the NE may slightly confuse the data as the Mound Builders lived in the Louisville area. The flood deposit was actually found near Louisville and would have drowned a considerable number of people – as well as displaying evidence of a lot of water being moved down from the north in the Mississippi-Ohio system. That doesn't sound like a drought – but it depends where the jet stream was situated, and where it was raining heavily. As noted previously the 15th century was warmer than the 14th (and the 16th and 17th centuries) so it could be that first the Mound Builders had to suffer a period of cold weather – followed by a great flood (on a par at least with the river flood of recent times). Interesting research. Although climate change is a theme it is not the be all and and all and relies on the actuality of a medieval warm period (which the hockey stick eradicated).