Should the Mayans be blamed for their own tragedy?

While doing my last blog I wondered…if we are now facing the consequences of exploiting our own natural resources, then could the Mayans also have contributed to the worsening of their own drying throughout the classic-postclassic period.

A recent paper by Medina-Elizalde and Rohling (2012) highlighted the fact that the ecological carrying capacity of the Yucatan Peninsula is highly sensitive to precipitation reductions. They found reductions in the frequency and intensity of cyclones over the Yucatan Peninsula which coincided with the collapse of the empire. They estimated this reduction is up to 40% mostly during the summer season. Did human influences on land cover intensify the drought condition?

Figure 1: Source Cook et al (2012) 

Figure 2: Source Cook et al (2012) 

Cook et al (2012) suggest deforestation by the Mayans had indeed influenced their climatic system to a drier mean state. Using a “new suite of climate model” they found a few interesting results:

Precipitation level

There result suggested an annual 5%-15% decrease in precipitation due to deforestation, located in regions with the most land cover change in Southern Mexico and Yucatan peninsula as shown in Fig.1 and Fig 2a. As Fig2b the reduction in precipitation is largely driven by 10%-20% reduction.

This modelling differed to Medina-Elizalde and Rohling (2012), hence it shows the constraints between using peloclimatic data and modelling. But both agreed that deforestation increases dryness.  

Figure 3: Source Cook et al (2012) 

Figure 4: Source Cook et al (2012) 

Driver of Drought

Modelling conducted here differed to Oglesby et al (2010) which found that drought was accelerated by thermal mountain effect. Cook et al (2012) paper showed that it was due to the reduction in available energy. From fig 3 we can see that the net radiation at the surface decreases. This can be explained by a shift from dense forest to domestic crops, which led to increases in the surface albedo.  Fig 3b also shows decline in laten heat, also due to the increased area of crops which has shallower roots and lower leaf area. Given the above factors, this would lead to a reduction of shallow convective cloud cover as shown in Fig 4a, and in turn lower levels of precipitation.  Fig 4b and 4c showed that deforestation leads to an increase in cloud top temperature. This would suggest a lower elevation of cloud tops and a reduction in cloud water content. They all point towards a lower convective activity which is consistent which fig 2b that shown a decreased in precipitation level  

Implication of results

Since the deforestation scenario uses peak population and deforestation level, it can be used as an analogue for the conditions during the 800-950CE. This provides an insight into the fact that the growth of the Mayans acted as a ‘double edged sword’. The extent of deforestation, and given the Yucatan peninsula has a high sensitive to precipitation change, they exemplified the drought that occurred. They estimated that deforestation contributed to between 12.5% - 60% of total drying. Coupled with the fact that the modelling showed the location of severe drought coincided with regional centers of the Terminal and Postclassic period, it further reinforeces the causality between climate change and political stability, demographic decreases and cultural change.  It is important to note that the stimulation does not answer the question of why the Southern Mayan lowlands collapsed before the more arid northern Yucatan.

The other side of the story

McNeill (2012) showed a host of sustainable engineering and policy that were implemented across Mesoamerica during the Classic period. This discussion extents Cook et al (2012) quantitative modelling and give more depth into our discussion.  Below are some of the examples:

The management of forest

a.     The elite certainly contributed: This is in the interest of the elite to maintain forests because it produces symbols of elitism, like deer and caco meat, valuable woods, jaguar pelts and bird feathers.

b.     A source of construction. In the city of Tikal, during the class Maya they used to use Manikara zapota (M.Z) woods which grow in moist tropic forest. Research showed they use freshly cuts woods instead of old trees (Lentz and Hockaday 2009) in AD766 the builders of Tika used a different tree called Haematoxylon campechianum L.  For 40 years they allowed for the M.Z trees to recovery before using it again as a construction material

c.     In the late classics, tropical forest were close to the city and there were evidence of the preservation of historic tress (Harrison 1999)

Farming Techniques

a.     Use of ridged fields, although not common, helps aerate the soil, concentrate topsoil and focus greater amounts of moisture around plants. One such example is the 6^th Century AD site of Ceren in El Salvador.

b.     Terraces were found across Lowland Mayan area (Wyatt 2008). With the aim of retaining, preserving and catching runoff soil. But Dunning (1996) noted not all places uses this technology, as in the case of Puuc Maya in the Yucatan Peninsula, despite being located in a hilly terrain.

McNeil (2012) rejects the idea that the Mayans of the late classic period should be blamed for the environmental devastation that was observed during that period. Instead, he champions the idea that the Mayans in the classic period learnt from their ancestors in the pre-classic era which caused environmental damages across Maya lowland through swidden agriculture. Out of necessity, the Mayans developed the above sustainable techniques to increase the efficiency of agriculture in order to satisfy demand.  At the end of the Classic period, some areas like Copan actually experienced an increased in forest cover (McNeil 2012).

Conclusion

There are inherent problems with modelling. The fact that the model Cook et al (2012) used could not incorporate spatial patterns of land cover change at a higher resolution and that uncertainties exist with the estimation of land cover changes could underestimate the effectiveness of the Mayan's sustainable technique and policy. However, not all places were implemented with these techniques and uncertainty lies within the extent that these sustainable techniques could increase agricultural output without deforesting more land. I believe that deforestation is inevitable and deforestation as Cook et al (2012) showed certainly have contributed to drier climates during between 800-950CE. However, uncertainty lies within earlier dates - within early and mid-classic period - where population growth/density were lower. This could imply sustainable agricultural technology could produce enough food without the need for Mayans to cause mass deforestation. In turn, the drying effect from deforestation should be much lower during the early/mid-classic period.  Nevertheless, the Mayans should take partial responsibility for exploiting nature. 

Analogy to modern society 

It is important to note Cook et al's is significant in the sense that if climatic change undermines our agricultural system in areas like Africa or Europe it could lead to wide spread social disorder or even war. Given we live in an age of globalization this will draw in others. Also, the paper highlights the dangers of deforestation and the 'knock on effects' it has in the climate system. McNeil's paper is equally important and it suggest to us that even though the Mayans are aware of the consequences of deforestation, and have ways of mitigating the effect through better technology, but they still fail to solve the inherent problem of sharing resources with too many people - especially when resources where decreasing due to climate change. This is an important lesson as our modern society should wake up, and not get dragged down by global institutions on climate reform and scapegoating the poor nations (see my last post here). We should start reforms within developing and rich nations TODAY.