Plows, Plagues, and Petroleum: How Humans Took Control of Climate

Plows, Plagues, and Petroleum: How Humans Took Control of Climate

Plows, Plagues, and Petroleum: How Humans Took Control of Climate

Plows, Plagues, and Petroleum: How Humans Took Control of Climate


The impact on climate from 200 years of industrial development is an everyday fact of life, but did humankind's active involvement in climate change really begin with the industrial revolution, as commonly believed? Plows, Plagues, and Petroleum has sparked lively scientific debate since it was first published--arguing that humans have actually been changing the climate for some 8,000 years--as a result of the earlier discovery of agriculture.

The "Ruddiman Hypothesis" will spark intense debate. We learn that the impact of farming on greenhouse-gas levels, thousands of years before the industrial revolution, kept our planet notably warmer than if natural climate cycles had prevailed--quite possibly forestalling a new ice age.

Plows, Plagues, and Petroleum is the first book to trace the full historical sweep of human interaction with Earth's climate. Ruddiman takes us through three broad stages of human history: when nature was in control; when humans began to take control, discovering agriculture and affecting climate through carbon dioxide and methane emissions; and, finally, the more recent human impact on climate change. Along the way he raises the fascinating possibility that plagues, by depleting human populations, also affected reforestation and thus climate--as suggested by dips in greenhouse gases when major pandemics have occurred. While our massive usage of fossil fuels has certainly contributed to modern climate change, Ruddiman shows that industrial growth is only part of the picture. The book concludes by looking to the future and critiquing the impact of special interest money on the global warming debate.

In a new afterword, Ruddiman explores the main challenges posed to his hypothesis, and shows how recent investigations and findings ultimately strengthen the book's original claims.


The research that led to this book began when I was a professor in the Department of Environmental Sciences at the University of Virginia, following my earlier career at Lamont-Doherty Observatory of Columbia University. I was able to interest undergraduate student Jonathan Thomson in a term-length research project that explored a mystery that had puzzled me earlier: the fact that methane concentrations in the atmosphere have risen for the last 5,000 years when everything I knew about the natural controls of methane predicted that a drop should have occurred instead. In 2001 we published a joint paper in the peer-reviewed literature attributing the anomalous methane trend to human activities.

After retiring early in 2001, I began working at home on a similar mystery—a rise in carbon dioxide concentrations that occurred during the last 8,000 years even though natural factors (as I understood them) again predicted a drop. The 2003 publication of a paper summarizing my new hypothesis of early human effects on climate coincided with a lecture at the annual American Geophysical Union meeting in San Francisco. More recently I have talked to university audiences far larger than earlier in my career. People are interested in and stimulated by this hypothesis, but acceptance of radically new ideas does not come quickly in science; the community is still sorting out their reactions, and the ultimate judgment concerning this hypothesis lies in the future.

Because the detective work that forms the central theme of this book draws on my four-decade experience in climate science, thanking everyone involved in this hypothesis (and thus this book) would be an endless task. Still, some thanks stand out from the rest. My background in understanding the impact of orbital variations on Earth's climate came from working with the CLIMAP group, among which John Imbrie was the guiding light and Nick Shackleton and Jim Hays were key members. My understanding of the effects of ice sheets and tropical monsoons on climate came from working with the COHMAP group, with John Kutzbach as primary “teacher” and Tom Webb, Herb Wright, and Alayne Street as important members. Work with John Kutzbach on the climatic effects of uplift of the Tibetan Plateau taught me about the uses and limitations of climate models. Collaborations with colleague Andy McIntyre and with my former graduate students Alan Mix, Ned Pokras, Glenn Jones, Maureen Raymo, and Peter deMenocal also expanded my horizons. In recent years, discussions with and/or publications by many others broadened my understanding of several aspects of climate and human . . .

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