The Early Anthropocene Hypothesis

The Early Anthropogenic Hypothesis

William Ruddiman argues that preindustrial agriculture dramatically altered the course of the Holocene, starting 8,000 years ago. The invention of rice agriculture in China, as well as the deforestation associated with it, increased levels of methane and carbon dioxide. This made the Holocene warmer and more stable than it otherwise would have been. These elevated greenhouse gases also contribute signficantly to modern global climate change.

The Holocene Anomaly

Ruddiman bases his claim on the observation that the Holocene is an anomaly when compared to earlier interglacial periods. Below is a graph of insolation trends for the current interglacial, as well as the previous four. The current interglacial is marked in red:

Insolation Trends

This correlates with:

Methane and Carbon Dioxide levels

(An explanation of stages can be found under Terms.)

The pattern of the Holocene is clearly different from that of the previous stages.

Gradient

This anomaly could be attributed to any number of things. One way to narrow down the possible sources is by determing where the increased greenhouse gases came from. Based on ice samples from Antarctica and Greenland, scientists have determined that the source must be tropical.

Natural Wetlands

Rice

Wetlands are a major source of methane. But the Holocene was getting drier when the methane increases, not wetter, making increased natural wetlands unlikely.

Rice Agriculture in China

One possible source is increased rice agriculture in China. Archaeological evidence supports this, since increased greenhouse gases correlate with increased population and evidence of agriculture throughout China.

Simulation study

A simulation study conducted by Vavrus, Ruddiman, and Kutzbach found that it was likely that pre-historic human activity prevented the onset of a new glacial period.

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