Early anthropocene

The early anthropocene hypothesis (sometimes called Early Anthropogenic) is a theory proposed by William Ruddiman. It posits that the Anthropocene era, as some scientists call the most recent period in the Earth's history when the activities of the human race first began to have a significant global impact on the Earth's climate and ecosystems, did not begin in the eighteenth century with advent of coal-burning factories and power plants of the industrial era, as was commonly assumed, but dates back to 8,000 years ago, triggered by intense farming activities of our early agrarian ancestors. It was at that time that atmospheric greenhouse gas concentrations stopped following the periodic pattern of rises and falls that had accurately characterized their past long-term behavior, a pattern which is explained by natural variations in the Earth's orbit known as Milankovitch cycles. In his overdue-glaciation hypothesis Ruddiman claims that an incipient ice age would probably have begun several thousand years ago, but the arrival of that scheduled ice age was forestalled by intense farming and deforestation by early farmers that began raising the level of greenhouse gases eight thousand years ago.

The overdue-glaciation hypothesis has been challenged on the grounds that comparison with an earlier interglaciation (MIS 11, 400,000 years ago) suggest that 16,000 more years must elapse before the current Holocene interglaciation comes to an end. Data from even earlier ice-cores going as far back as 800,000 years ago suggest probable "cyclicity" of interglacial length and an inverse correlation with the maximum temperature of each interglacial. But Ruddiman argues that this results from a false alignment of recent insolation maxima with insolation minima from the past, among other irregularities which invalidate the criticism.

References

* [http://www.evsc.virginia.edu/faculty/people/ruddiman.shtml William Ruddiman's home page]
* [http://www.sciam.com/article.cfm?articleID=000ED75C-D366-1212-8F3983414B7F0000 How Did Humans First Alter Global Climate?]
* [http://courses.eas.ualberta.ca/eas457/Ruddiman2003.pdf The anthropocenic greenhouse era began thousands of years ago; Climatic Change 61: 261–293, 2003]
* [http://www.realclimate.org/index.php/archives/2005/12/early-anthropocene-hyppothesis/ Debate over the Early Anthropocenic Hypothesis]
* [http://www.pages-igbp.org/products/posters/EPICA1final.pdf The EPICA Challenge: Predicting CO₂ Over 800,000 years]