Over Population and The Theories of Climate Change
By the late classic period (900 A.D.), the Mayans had passed their glorious prime. The success of their socioeconomic and political systems, along with their complex farming methods and centuries of abundant rain, created an increase in population and by the eighth century it is estimated that the bajos- lowlands, were occupied by tens of thousands of people. This in turn put enormous stress on their fragile ecosystem.
Some researchers, such as Robert J. Sharer and Loa P. Traxler, say that over population coincides with environmental changes. There are two variations of the theme, first being self-induced environmental changes. The Mayans had an extremely advanced farming technique. It was thought the only way to farm in such a jungle environment would be to use the slash-and-burn technique, which is widely used today in Petén, Guatemala. It is when a section of the forest is burned down, fertilizing the soil. However, it only lasts for three to five years before it is exhausted. It was discovered that the Mayans constructed large scale water-collecting systems which were used for the irrigation and drainage of crops throughout most of the bajos which was largely swamp land. The farming intensified as a response to overpopulation and the high demand for food put stresses on the available land and water. This resulted in monocropping, over-use of land and deforestation, causing soil erosion, loss of fertility and increased water shortages.
Evidence provided from sediment cores taken from the central lakes in Petén provides confirmation of human-induced environmental changes. Geologists Larry Peterson and Gerald Haug say that sediments came from immense runoffs of agricultural soils exposed by deforestation. The evidence throughout the bajos suggests that the destruction of the forest could have depleted the lands capability to sustain the growing population. Thus causing mass agricultural failure, famine, and forced abandonment of much of the bajos.
In addition pollen data was acquired from the lake Puerto Arturo in the Mirador Basin. Evidence suggests that there was an abrupt drop in grass, weed and agricultural pollen and by 960 A.D. the pollen numbers plummeted to near zero values which have been consistent ever since. Further evidence that suggests human induced environmental changes was discovered by studying the thickness of the lime plaster floor stones of the temples. It is estimated that they would have needed twenty trees to create a fire that could produce a floor stone of one square meter. Researchers found that the earliest temples started at a foot thick but got thinner as the years progressed.
Atmospheric scientist Bob Oglesby says, “if we completely deforest an area and replace it with grassland, we find that it gets considerably warmer- as much as five to six degrees Celsius.” This happens when sunlight that usually evaporates water from the canopy, starts to heat the ground instead because there are no trees to block the suns rays. Oglesby thinks that deforestation contributed to a drought, but lake sediment cores indicate that the deforestation was coinciding with the natural climate that was already producing a drought.
The second variation of the theme of climate change is that it was beyond human control. The Mesoamerican region is in fact a seasonal desert. Ninety percent of its moisture falls between June and September (summer) and the dry season runs from January to May (winter). NASA researchers say that this is due to the Intertropical Convergence Zone or “meteorological equator,” this is a region near the equator, where the trade winds of the northern and southern hemispheres meet. The convergence of these trade winds forces the air to rise and once it cools it begins to rain, where in the winter months the intertropical convergence zone shifts and dry conditions overcome the Yucatan peninsula and northern South America.
Peterson and Haug contributed greatly to the understanding of the climatic conditions and proclaimed the drought theory was a major contributor in the collapse. Their evidence comes from the northern coast of Venezuela in a continental shelf named the Cariaco Basin. It is about a kilometre deep and acts a sediment trap, by preventing its waters mixing with the ocean to the North; as a result there is no dissolved oxygen to sustain life. The absence of burrowing organisms means the sediment floor remains intact. This enables scientists to analyse pristine levels of strata. There are light and dark layers, the light layers indicate little to no rain; this is due to when the plankton dies their remains create the layer for that season, and in the rainy season sediment falls into the water creating a dark layer. Even though Venezuela was not inhabited by Mayans, both regions sit under the same area of the intertropical convergence zone, so it would be accurate to say that they would experience parallel weather patterns.
Further experiments were executed on the sediment cores. These included measurements of titanium and iron, which would appear in the remains of plankton. High levels would suggest rain, and low levels would suggest drought. They also used x-ray fluorescence, which uses x-rays to illuminate a sample and measure the amount of light given off. This reveals the concentration of various elements in the sample.
Another technique utilized is called “micro” x-ray fluorescence, designed for small samples and can measure the layers at two months at a time. Peterson and Haug measured two slabs at an interval of about 200 to 1000 A.D. and revealed four distinct layers of titanium minima which are considered to be multi-year droughts. The radiocarbon measurements of these samples indicate they occurred in A.D. 710,810, 860 and 910, give or take 30 years from the slight unreliability of the radiocarbon dating technique. However, anthropologist Arthur Demarest thinks, “that a drought had little to do with it,” since the region is a seasonal desert and as research above shows they experiencing drought before.