Early Agriculture & Anthropogenic Climate

A quick note on the publication of the updated rice archaeology database and a model effort based on it examining the spread of rice with an attempt to test its hypothesized contribution to rising global methane levels between 3000 BC and 1000 AD. This was a team effort involving students and post-docs with Early Rice Project (Kingwell-Banham; Castillo; Weisskop; Qin Ling) collaborators from abroad (Sato (Kyoto); Hijmans (David)) and some nice GIS modelling work by Jacob van Etten (Madrid). Some maps wet rice distirbution in selected  time-slices are shown left; but for more details read the paper.  This article "The contribution of rice agriculture and livestock pastoralism to prehistoric methane levels" is available ahead-of-print on-line from The Holocene.  Our key conclusion is that by 1000 AD perhaps 80% of 'anomalous' methane could be attributed to rice cultivation but also at 2000 BC rice is still not that significant and other sources should be sought such as the rapid spread of pastoralism around this period especially through the savannas of Africa and South Asia.

I have previously blogged the rice-part of the Ruddiman (Early Anthropogenic) hypothesis i.e. that early rice framing (and its spread) contributed enough extra methane to the atmosphere to make a global impact from sometime just after 3000 BC. I did raise some questions about the quality of the data: how many early rice finds actually represent cultivated rice (not wild) and how many represent flooded or paddyfield rice rather than upland rainfed rice? Also what role did the spread of cattle pastoralism over the Old World play in contributing to Mid-Holocene methane levels? So this new paper is an attempt to address some of these questions. We make a first stab at mapping the areas over which pastoralism spread in addition to modelling the spread of rice and the land area under wet rice cultivation. For rice at least we are able to estimate methane output but further work is needed for an equivalent calculation from cattle. I think we also would all admit that our estimate from rice remains imperfect and there is a lot of additional work to do! Collecting better quality archaeobotany (and more of); more zooarchaeology; and more sophisticated modelling...

A recent summary of the Early Anthropogenic Greenhouse Gas hypothesis has been published on-line by Bill Ruddiman at realclimate.org. It has attracted a lot of discussion. Essentially this provides a preview to some of the results due out in the August issue of the journal The Holocene (although many of the paper are already available on-line). This issue has also received attention in Nature in their News section (in March) and was one of the issue debated at the AGU Chapman conference in Santa Fe in March.

Global Human Ecology: Anthromes from Biomes

A very interesting and important approach to mapping global vegetation but including the human activities has just come to my attention. It is the work of "Anthromes Project" of the Landscape Ecology laboratory at University of Maryand Geography Department, lead by Dr. Erle Ellis. Essential they are mapping landuse and vegetation together. Rather than traditional biome and vegetation mapping, which attempts to infer "potential vegetation" on the assumption that such maps represent the world as it would be if there were no humans present, they are explicitly mapping human environments, villages, rice fields, pastoral rangelands, as well as woodlands and 'wild' vegetation. Their results can be found on their website, and are discussed in a fascinating, if somewhat frightening, new paper "Anthropogenic transformation of biomes 1700 to 2000 [AD]" in Global Ecology and Biogeography. Essentially they demonstrate that the proportion of the earth's habitable surface (i.e. not under ice or ocean) has shifted from a majority wild to the majority human-managed and modified in the past 300 years. While we think of the world becoming increasingly urban, certainly true, it is the the expansion of inhabited villages that really stands out-- although as someone who has traveled across much of India and China, this is totally understandable, there is a vast number of sprawling small communities (often with populations in the many thousands) scattered across the landscape, and these are of course surrounded by crops (dry or irrigated), rice fields, and scrub vegetation used for grazing where "potential forests" ought to be. If the Neolithic is about the domestication of a few plants and animals, the plastic-age is about the domestication of the planet Earth.

As an archaeologist interested in past land use and vegetation, one is well aware of the need to factor in human activities in local environments (a point we tried to make in a little book on South Indian woodlands), and to keep in mind that people of have been playing with fire (literally) and modifying vegetation for a long time (at least 50,000 years in Southeast Asia and Australia, to judge by microcharcoal records of biomass burning). Agriculture, of course, represents a major transition in terms of intensifying modification and management of environments, but essentially much of that was still localized in a wider less modified background. The anthromes maps show clearly how precipitously the shift has occurred to a majority managed, modified and inhabited. As they conclude, it is clear that environmental research must focus on better modelling, predicting and managing human-centered ecologies, or as is noted in their blog the "war with nature" has already been won (for better or for worse) by culture, and we better deal with aftermath.

There is a conceptual parallel here with domestication. As seems increasingly clear to me, a key threshold is crossed when domesticated/human dependent crops (such as non-shattering rice) come to dominate the population, and the economy shifts to modifying the landscape and depending on domesticates. This is when agriculture emerges from early pre-domestication cultivation or small scale food production, and in many regional histories there is no going back to hunting-and-gathering after this. For better or worse people become 'trapped' and entangled in agriculture (see one recent exploration of this entanglement in World Archaeology) 

Returning to the anthropogenic biosphere, archaeobotany has a role to play in putting an even longer term perspective on these changes in biomes/anthromes. By accessing evidence for earlier periods of human use and modification of landscapes and the construction of agricultural landscapes and economies, we see how current and recent trends compare with and are informed by a longer perspective.