Climate Change and Collapse?

Yesterday marked the beginning of a critical fortnight in the future of climate change mitigation and adaptation. As I am remaining cautiously optimistic that COP21 will not be another Copenhagen catastrophe, I hope to be able to discuss some of the relevant outcomes of these talks over the coming weeks.

For now though, I want to obtain a more in depth understanding as to how climate may have shaped society and settlement distribution in the past. Many factors are known to impact upon societal stability, but I will aim to present the scientific evidence for a climatological influence in past collapses. I have briefly discussed this in relation to sea level rise previously, but what about the implications of an absence of water? In modern society, drought imposes significant implications economically, environmentally and socially. But it may have also been responsible for some dramatic events historically.

Recurrent periods of aridity are thought to have played a large part in the complex history of the Maya, in the Yucatan peninsular; a history which can be characterised by a cyclic rise and fall. As described by Alley et al. (2003), Mayan society flourished prior to 150 AD when the first collapse was thought to occur, evident by concurrent abandonment of many of their cities. However, it recovered and bloomed again up until 750-950 AD, where a demographic disaster resulted in the end of classic Mayan civilisation. They were a very advanced society for their time; using complex irrigation systems to allow agricultural activity in the Yucatan lowlands. However, something must have occurred which they were not able to recover from.

Haug et al. (2003) looked at the sediments within the Cariaco basin; an ideal proxy record owing to being closely situated to the former Mayan settlements, and because it is annually laminated, created by the movement of the ITCZ. Ti levels within the sediments clearly mark an increase in aridity around 760 AD, but significantly wetter conditions prior to this. Therefore, they suggest that the previously climatically favourable conditions allowed for rapid population expansion, which may have consequently exceeded the carrying capacity. Thus, when drought set in, resources were too scarce to support such an extensive society. This can be independently verified by a separate paleoclimate record in the Yucatan.

However, this incredibly complex phenomenon cannot be described by one model alone. Regional diversity in the collapse of society, is evident, which has led some to doubt the control of climatic variables. However, Haug et al. (2003) argue that the presence of a number of drought episodes superimposed upon a period of hyper-aridity may have resulted in a very drawn out process. This, in conjunction with the individual regional water resource availability, is thought to have contributed to this stagger.  

Ultimately, there is currently no single mechanism that can account for the significant demise of what was a very complex, sophisticated and seemingly advanced society. However, the increased appearances of drought years, although certainly not the only factor, does appear to have played a very important role. Thus, it will be interesting to see whether or not this serves as an analogue for the future, in what is expected to become an increasingly arid world.