Deforestation from Classical Period (~1000BCE and on) mettallurgy in the Holy Land dramatically amplified the effects of an otherwise small regional trend towards a warmer and drier climate. Before 10,000 years ago, we were in a different geological and human era and you can’t say too much about civilization. But starting at 10,000 until 2,000 years ago that part of the fertile crescent is known to have been fertile. And from 2,000 years to the present, it has been a desert. On learning about metal, locals supported their furnaces by making the region one that is no longer covered in forests. The authors of the paper below showed that semi-arid climates are particularly vulnerable to the kinds of changes caused by humans. “Water availability” is the important variable for life on the ground. In semi-arid climates, a large change in rainfall actually has little effect on water availability. However, a large change in ground cover (trees) has a huge effect. Trees hold water, in and on themselves, but their biggest role is keeping soil in place. A tablespoon of healthy soil has the surface area of a football field, making soil one of the best ways to keep water in an ecosystem.
This is all from a very academic, but really fascinating interdisciplinary book “Water, Life, and Civilisation.” A bunch of people out of U. of Reading in the UK had a multi-year project to reconstruct ancient climate and habits. They went across disciplines (meteorology, geology, archaeology, paleontology, biology, sociology, geography) and therefore methods (lit reviews and metaanalyses, digging (taking biological samples, cultural samples, building samples, rock samples, water samples, cave samples, and other fieldwork), qualitative fieldwork, policy analysis, computer simulation, model fitting, GIS, carbon dating, isotope dating, and agricultural experiments. They even invented some new methods under the heading of archaeobotany). With these methods you gain amazing insight into the past. The authors can show how bad floods got, that wells dried up, that agriculture was adapted for dry vs. wet climates, and that populations swelled or dwindled.
Focusing on one site, Wadi Faynan in southern Jordan, they show high absorption of water by soil (“infiltration”), less runoff, and less evidence of floods during the early and middle Holocene (12—5 thousand years before present). “This hydrological regime would have provided an ideal niche for the development of early agriculture, providing a predictable, reliable, and perennial groundwater supply, augmented by gentle winter overbank flooding.” By contrast, “During the late Holocene (4, 2 ka BP), the hydrology of the Wadi Faynan was similar to that of today, a consequence of reduced infiltration caused by industrial-scale deforestation to support metallurgical activity.”
A review of regional and local vegetation histories suggests that major landscape changes have occurred during the Holocene. There appears to be consensus that the early Holocene in the Levant was far more wooded than the present day (Rossignol-Strick, 1999; Roberts, 2002; Hunt et al., 2007), as a consequence of small human populations and prevailing warm, wet climates. Since mid-Holocene times, the combined trends of increasing aridity and human impact upon the landscape have combined to cause deforestation and erosion of soils. In Wadi Faynen, there is clear evidence that Classical period industrial activity would have played a significant role in this process. We propose that these changes would have greatly reduced infiltration rates in Wadi Faynan since the middle Holocene.
This chapter stood out for looking at how humans influenced climate, where all of the others focused on the equally important subject of how climate affected humans. But this was just one fascinating chapter of a fascinating book. A lot of the meteorology and geology was over my head, but using computer simulations calibrated on today and other knowns, and managing their unknowns cleverly, they got a computer model of ancient climate at the regional scale. Using that they got various local models of ancient precipitation. They complimented that guesswork with fieldwork in which they used the sizes of surviving cisterns, dams, gutters, roofs, and other ancient evidence of water management to estimate the amount of rainfall, the extent of floods, the existence of this or that type of sophisticated irrigation, and other details at the intersection of hydrology, archaeology, and technology. They learned about how resource limits constrained human settlements by examining regional patterns in their placement: early and high settlements tended to be near springs while later on they tend to be on the roads to larger cities. They used extra clever carbon and nitrogen dating to learn what the livestock were fed, what the humans were eating, and if a given area had mostly desert or lush plants. They can prove using differences in the bone composition of pigs and goats from the same period that they were raised on different diets. And with almost no evidence from surviving plants or surviving fields they were still able to infer what plants were being cultivated, and by what kind of sophisticated agriculture. Every plant makes microscopic sand crystals and in arid environments, these crystals are the same for plants grown yesterday and plants grown thousands of years ago. Because different plants grow crystals of different shapes, they were able to identify date palms at 1000 years before date palms were thought to have been domesticated. The crystals also shed light on ancient irrigation technology. By growing some grain crops with different kinds of technology and examining the resulting crystals, they showed that the clumpy crystals they were finding in ancient sites could only have come from grain fields with sophisticated irrigation systems.
Altogether, I’m impressed by how much we can know about ancient life and climate when we combine the strengths of different disciplines. I’m also afraid. For me, the natural place to go from here is to Jared Diamond’s Collapse for more examples of how civilisations have followed the resources around the world and then burned them down, and for what we might be able to do about it.
The book was Water, Life, and Civilisation; Climate, Environment, and Society in the Jordan Valley (Steven Mithen and Emily Black Eds.) Cambridge Universiity Press International Hydrology Series. The chapter I focused on was number fifteen:
Sean Smith, Andrew Wade, Emily Black, David Brayshaw, Claire Rambeau, and Steven Mithen (2011) “From global climate change to local impact in Wadi Faynan, southern Jordan: ten millenia or human settlement in its hydrological context.”