Some conclusions and final thoughts

Archaeology is the study of the behaviour of humans and societies through their material culture. This material culture obviously includes the familiar pottery and metal artefacts. It also includes the effects of food resourcing and subsistence behaviours, ecofacts and cultural landscapes. Archaeology can tell us what humans did where and when, and then attempt to determine the how and why.

Geography studies the formation and change processes of the environment, the atmosphere, the biosphere and so on, and the interaction of humans with that environment. When the behaviour of humans and human societies achieves a level of impact on the environment that equals or exceeds the impact of natural forces we have an Anthropocene. Geography can determine the consequences of human behaviour.

The imperative of Neolithic farmers was survival. Low population densities meant that when new agricultural technologies impacted on their environment they could change location or revert to older technologies such as hunting and gathering (Lewis-Williams and Pearce, 2009, pp.21-2; p.95). Long-term environmental and climatological impacts were either invisible to those farmers or not linked causally in their thinking, instead they blamed the "sky gods" (Barker, 2006, pp.409-10).

Our contemporary society has become all too aware of the environmental impact of human behaviours. Overwhelming scientific evidence has started to persuade governments and individuals to try and mitigate their impact on the environment. The “western” industrialised nations are at the forefront of this debate with arguments over the need for economic growth set against environmental consequences (Everett et al., 2010).

Let us optimistically suppose that the environmental impacts of industrialisation and burning of carbon fuels can be reversed, that the consumer society can become carbon-neutral by reducing demand for consumer goods and/or by deploying green technologies. Will that stop the impact of human behaviour on the environment? The evidence presented over the previous blog-posts suggests that agriculture also has a significant role in climate change.


Always read the small print (Source)

A Google search for “agriculture and climate change” revealed as much concern about how climate change might affect agriculture as vice-versa, with some articles (e.g. this EPA article) noting some positive effects. Should we follow the industrial model and reduce demand for food while deploying green agricultural technologies? Reducing demand for food poses some difficult moral questions because, as we have seen, increase in demand for food is related to increase in population. Who has the right to demand that an individual or a community or culture reduce their birth rate?

This is why the science must be on very solid ground about the processes of anthropogenic and natural climate change, and their relative impacts and long-term consequences. Studying the Anthropocene and its origins and consequence is an essential part of establishing that solid ground.

A final thought - mitigating the consequences of industrialisation and agriculture would still leave the natural, systemic climate change processes in place, driven by geological and orbital forcing. Should humankind attempt to mitigate the effects of those forces in order to maintain a comfortable stable environment for ourselves?

Thank you for reading this far. I hope I have provided some food for thought as well as a fertile source of intellectual nourishment on the subject of the Anthropocene.



References cited not available online:
Barker, G., 2006. The agricultural revolution in prehistory: why did foragers become farmers? Oxford: Oxford University Press.
Lewis-Williams, D. and Pearce, D., 2009. Inside the Neolithic Mind. London: Thames and Hudson.

So was it the farmers or the factories?

I thought it would be useful to summarise the key points from the evidence and findings in my previous posts:

• The Earth’s climate is driven by orbital forcing, changes in the tilt and orbit of the earth around the sun, which causes predictable changes to climate over the long term because of the variation caused in the amount of sunlight falling on the planet’s surface
• These climactic variations may be detected using methane and carbon captured in polar ice as proxies
• The changes in atmospheric methane and carbon concentrations since the last Ice Age do not follow the predicted model; both would be expected to fall as temperature falls towards the end of the interglacial period but they do not
• Atmospheric carbon starts to rise about 8,000 years BP and methane starts to rise about 5,000 years BP; both gases are now at concentrations significantly above the expected levels and are continuing to rise
• The Neolithic adoption of farming led to widespread forest clearances, which can raise atmospheric carbon levels, and the domestication of animals and the introduction of irrigation, both of which can raise atmospheric methane levels
• Determining the rate at which agriculture spread is necessary as part of establishing a causative link with the anomalous atmospheric gas concentrations
• Agriculture does not only impact the atmosphere; it also changes soils, leaving a permanent geological marker the dates for which tracks its expansion
• Geological events, such as oceanic slides, are potential sources of atmospheric methane and carbon
• Agriculture causes soils and sediments to be transported downslope, creating recognisable geological markers and potentially releasing carbon to the atmosphere

The global impact of humans on the environment clearly started before industrialisation. The markers left by agriculture are widespread, geologically detectable and securely datable. The evidence pulls the start of the Anthropocene well before the inception of industrialisation and the dependence on carbon fuels.

So, to answer the question, the evidence does support the proposition that:

The Anthropocene was started by farmers



Neolithic farmers processing manure (BBC, 2013)

Whether the start of the Anthropocene can be dated to 5000 BP or earlier is not so clear. Ruddiman and other researchers are building a compelling case but there are many alternative factors which might have caused short-term changes in atmospheric methane and carbon and which might have either contributed to the anomaly or caused a tipping point to be reached leading to long-term effects.

 

It is possible that some climate-affecting geological events could be unknown or opaque. For example, the outflowing of Lake Agassiz is associated with initiating the Younger Dryas stadial, but there is disagreement as to whether this huge body of cold fresh water flowed east (Broeker et al., 1989; Hostetler et al., 2000) or west (Murton et al., 2010) so models of the long-term effects on climate have a large margin of uncertainty.

 

We have established a layered structure of processes affecting atmospheric carbon and methane:

• Orbital forcing - a relatively predictable and long term symphony of cycles that span glaciations
• Geological forcing - unpredictable events that do not recur between glaciation cycles, including earthquakes, sub-oceanic slides, bolide impacts, volcanoes, etc.
• Agricultural forcing - the anthropogenic effect that emerged and expanded during the Holocene
• Industrial forcing - the anthropogenic effect that emerged and expanded during the last two centuries

All of these forces have been shown to drive environmental change. The problem for environmental scientists is in disentangling their relative effects.

 

 

Soil erosion and atmospheric carbon

We have seen that intensive agriculture requires soils to be processed, enhanced and engineered to maximise productivity. The soils that surround the Mediterranean basin are poor; their structure is weak and there is little organic material. Clearing the land of natural flora to create fields removed the root structures which consolidated the soil. Ploughing destroyed what little soil integrity existed and intense rainfall washed the dusty soils into valley bottoms (García-Ruiz, 2010; Romano et al, 2013, pp.115-6).

The phenomenon of alluviation into Mediterranean valleys was originally observed by Vita-Finzi (1969) and expanded by Leopold and Vita-Finzi (1998) who identified two phases: the reddish  "Older Fill" dating between 30,000 and 10,000 BP and the grey-brown "Younger Fill" dating to between AD 400 and AD 1850. The very fact that a geological structure can be identified across a region and for it to be strongly linked with human activity is supportive of the argument for an Anthropocene. It must be acknowledged, however, that the evidence for a direct causal link is equivocal, for example see Ackerman et al. (2014, pp.239-40), who note that erosion may actually be caused by the abandonment of farming infrastructure, as does García-Ruiz (2010).


1. Abandoned farms, 2. Crops in hills, 3. Steep vineyards, 4. Steep olive and almond orchards, 5. Soils degraded by irrigation. (García-Ruiz, 2010, p.2)

Van Oost et al (2007) considered whether this type of soil erosion could cause organic carbon in soil to be released into the atmosphere. Having surveyed a wide range of soils samples from Europe and North America, they concluded that the eroded material is burying carbon in the places to which it is transported and that carbon is sequestered in the eroded locations. They concluded, controversially, that the effect of erosion on atmospheric carbon is neutral; agricultural erosion does not offset the fossil fuel contribution, neither does it contribute to atmospheric carbon. In response, Lal and Pimentel (2008) argued that soils exposed by erosion take up carbon slowly, that the transport of eroded soils releases carbon and that the deposition of eroded soils releases methane.

Kuhn et al. (2009) considered the relationship between soil erosion and the carbon cycle in more detail. They highlighted three issues which impact on the process:

1. Interrill erosion is the movement of soil across a surface caused by the impact of raindrops loosening the soil structure and the splash of raindrops transporting material. It affects organic material more than inorganic material and so has the effect of concentrating organic carbon in interrill sediments by up to 50%. This surface concentration has the effect of increasing the carbon exchange with the atmosphere.
2. Rill erosion is the transport of soils and sediments by the action of flowing water. This action moves material downslopes and sorts material by size (Goldberg and Macphail, 2006, pp.72-84). The sorting and transporting preferentially affects organic carbon material compared with mineral sediments, creating concentrations of organic carbon-rich soils and carbon-poor sediments at a rate not found in nature.
3. Erosion system stationarity concerns the assumptions that (i) the erosion rate is consistent and that (ii) there is a linear relationship between soil erosion and the release of organic carbon. In fact upper soil horizons are organic-rich and therefore carbon-rich. The release of carbon through erosion thus diminishes over time as the richer horizons are removed (though this ignores any effects of manuring and other agricultural soil enrichment activities).

These issues do not offer a conclusion as to whether Van Oost et al. were correct. They do, however, demonstrate that agriculture changes the dynamics of soil erosion, and that those dynamics affect the exchange of carbon between the biosphere and the atmosphere. Agriculture thus leaves more permanent markers in our environment.

This post reads more like a section from an academic essay than a blog. That is because I thought it was important to show that answering my titular question: "What Started the Anthropocene, Farming or Factories?" is not about showing that Ruddiman, or anyone else, is right or wrong. It is about understanding the range of independent and interdependent processes that are caused or impacted by human activity and quantifying their effect on all aspects of our environment.


References cited not available online:
Goldberg, P. and Macphail, R., 2006. Practical and Theoretical Geoarchaeology. Oxford. Blackwell Publishing Limited.
Vita-Finzi, C., 1969. The Mediterranean Valleys Geological Change in Historical Time. Cambridge. Cambridge University Press.