My research, in collaboration with colleagues at the University of Wisconsin, focuses on comparing the observed climate of the last 7000 years against the way it would have developed in the absence of early anthropogenic alterations caused by agriculture. Beginning 7000-5000 years ago, early farming added substantial amounts of CO2 and methane to the atmosphere. Had this not occurred, climate would have cooled substantially, particularly at high latitudes, and small ice sheets would have begun to develop at high northern latitudes. 

One part of our approach (under my responsibility) has been to incorporate the wide range of multi-disciplinary research that has recently provided ground-truth evidence of agricultural transformations of Earth's surface, with resulting emissions of greenhouse gases. Deforestation emitted significant amounts of CO2 beginning 7000 years ago, and rice-paddy agriculture and tending of livestock emitted substantial methane after 5000 years ago. Several published papers by Ruddiman have synthesized these new developments.

My Wisconsin colleagues have used this ground-truth evidence to run two simulations on the NCAR CCSM4 climate model covering Holocene millennia. One simulation covers the observed evolution of climate (including the anthropogenic overprint), and one simulates the climate that would have developed withpout anthropogenic interference. Progress on this time-intensive modeling work has recently been slowed by an unexplained crash of the NCAR model that is now being examined.  

We have also published an influential paper on marine isotopic stage 19, the closest interglacial analog to the current interglaciation. During that interglaciation, CO2 fell to lower values close to those predicted by our early anthropogenic hypothesis, and ice cover developed in several far-northern regions, also as predicted.    

Our research has attracted wide attention from many scientists, who have published several dozen papers, some favoring and some opposing our hypothesis of early anthropogenic interference in the natural operation of the climate system. The resulting debate has also been widely covered in mainstream media.  

I (WFR) have also recently voiced my criticisms of the underway attempt by the Anthropogenic Working Group of the Subcommission of Quaternary Stratigraphy of the Geological Society of London to formalize the start of the "Anthropocene" at or around 1950. My basic counter-argument is that widespread alterations of Earth’s surface began 7000-5000 years ago. For example, full deforestation (reduced to modern levels) had occurred in most regions a millennium or more ago.

Last Modified: 05/31/2019
Modified by: William F Ruddiman