Plows, Plagues and Petroleum

plows plagues and petroleum

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

By W F Ruddiman

Princeton University Press (2010)

Book Review

In Plows, Plagues and Petroleum, paleoclimatologist W F Ruddiman makes the argument that the human species began interfering with climate – by increasing CO2 emissions – long before they began burning fossil fuels during the industrial revolution. After studying millions of years of ice core records, Ruddiman concludes that agricultural activities that began roughly 10,000 years ago increased atmospheric CO2 sufficiently to reduce planetary cooling and reduce a long overdue ice age.

Ruddiman’s book carefully traces the domestication of local plants and animals that occurred simultaneously in Mesopotamia, China, Africa and the Americas between 8,500 and 4,000 BC. Plant and animal domestication was accompanied by large scale clearing of forest land for fields and pasture. This massive loss of trees was accompanied by a big increase in atmospheric CO2.

Ruddiman has always been curious about periodic drops in CO2 concentrations that began around 540 AD. Theorizing that these dips correlated with temporary declines in global population, he examined historical records for evidence of wars, famines and pandemics that might have wiped out large numbers of people. What he discovered was a close link between infectious epidemics and declines in CO2 concentrations, as forests reclaimed large swaths of agricultural land.

The first epidemic in the recorded history was an outbreak of bubonic plague in the Roman Empire in 540 AD. By 590 AD, it had wiped out 40% of Mediterranean Europe. European plague outbreaks continued to occur every ten to fifteen years until 749, when a long plague-free period was accompanied by a rebound in population growth, deforestation and atmospheric CO2. By 1089, virtually all of Europe was deforested.

An even more severe plague pandemic occurred in the mid-1300s, wiping out a third of Europe (25 million people). In some cities, mortality rates were as high as 70%. The resulting labor shortage gave serfs who survived immense bargaining power. As they moved from estate to estate seeking good working conditions, they began to be treated as tenant farmers rather than slaves.

There were new plague outbreaks, accompanied by reduced atmospheric CO2, in the mid-1500s and mid-1600s.

The large pre-industrial drop in CO2 emissions occurred with what Ruddiman refers to as the North American pandemic (1500-1750. This was caused by the arrival of Europeans – who Ruddiman describes as flea infested, lice ridden peoples who shunned bathing – with a host of illnesses (smallpox, influenza, hepatitis, diphtheria, measles, mumps, whopping cough, scarlet fever, cholera and plague) to which native populations had no immunity. This was in addition to untold numbers of natives slaughtered by Europeans.

Prior to the arrival of Europeans, the population of North America was estimated between 50-60 million. Ninety percent (50 million) would die over the next 250 years. This amounted to 10% of the global population. Nearly all their agricultural settlements were reclaimed by forest, resulting in the third and largest pre-industrial drop in atmospheric CO2.

Download a free PDF of this book at Plows, Plagues and Petroleum

10 thoughts on “Plows, Plagues and Petroleum

  1. Wonder if the world grew the hell out of industrial hemp it’d put a dent in CO2 levels. Some reports on hemp make the claim. And who’s leading the charge on reforestation while all the noise blares about climate change. Like dad used to say “they know what to do, they just won’t do it.”


    • I’m really impressed by some of the reforestation happening in Africa. Especially the work of the late Nobel Peace Prize winner Wangari Maathai. As it happens, I’m part owner of a hemp farm here in Taranaki. In New Zealand, it’s legal to grow hemp with a license. We have a local builder specialized in building hemp house, who also manufacturers hemp oil out of our product. It turns out that hemp oil is more effective in treating cancer because it has higher concentrations of cannabidiol (at least ours is).


  2. On the issue of global warming, I’m not entirely certain that the ‘science,’ — leaving aside for the moment what very much appears to be a politically concocted ‘scientific consensus –‘ has ‘proven’ anything conclusive about the role that CO2 plays in the overall warming and cooling trends of the planet.

    Certainly, I do not doubt the correlation between increased human activity and increases in CO2 concentrations in the atmosphere, or that humans today are primarily responsible for the destruction of the environment on a global scale.

    But is it, for example, an increasing human population (and an increased concomitant mass agricultural activity) that drives climate change? Might it not be the opposite, with the one possibly feeding back into the other — or not? Environments become more accessible and habitable to greater numbers of people to the degree that their climates trend toward the warm end of the hospitable temperature spectrum, and as the number of inhabitants increase, so do the CO2 emissions. What I’m suggesting is that although climate change may be happening, though the planet may be warming, though clearly large scale human activities are in fact having a most deleterious impact on the environment, it may just be that ‘climate science’ is as yet too immature in its development to be able to assert anything with confidence as to the degree of influence human activity, in its CO2 emissions, is having on global mean temperatures.

    As an example that the science may yet have some ways to go, and for those of you who might not have heard of Henrik Svesnmark, a link for you:

    A couple of video introductions to a research project headed by Dr. Jasper Kirkby and that follow up on Svesnmark’s hypothesis can be found here:


    The nub of the Svesnmark and Kirkby investigations is roughly as follows: there is a well established and undeniable correlation between solar magnetic cycles and cycles of global warming and cooling. Svensmark has established that when the solar magnetic field peaks in strength, the surface temperatures of our planet tend to be markedly warmer; and when the solar magnetic field ebbs to its weakest, the surface temperatures of our planet tend to be markedly cooler.

    Svensmark’s hypothesis for explaining these (paleoclimate) correlations is that cosmic rays raining down on our planet from disparate parts of the sky play a crucial role in building up the particulate aerosols necessary to the genesis of clouds. The denser the flux of cosmic rays raining down on us, the denser become the cloud forming aerosols in our atmosphere, and the more clouds we have overhead to counter our sun’s radiative heat emissions. The density of the incoming cosmic flux, given its ionized and therefore electrically charged state, varies according to the intensity of the sun’s fluctuating magnetic field: the more intense the solar magnetic field, the more attenuated, because deflected, the cosmic flux will be, and conversely.

    It remains for the Svensmark’s hypothesis pertaining to the influence of cosmic rays on aerosol formation to be confirmed or disproved. ‘The Cloud Experiment’ at CERN being conducted under the supervision of Jasper Kirkby intends to do just that.

    Now consider that if Svensmark’s speculations find corroborative support from Kirkby’s experiments, climate and weather events on earth will be shown to be influenced by, amongst other things, distant cosmic events. Such events lie beyond the scope of any reliable weather or climate forecasting methods we currently possess. If it is demonstrated that distant cosmological events are themselves a source of significant climactic ‘forcing,’ climate forecasting becomes at least in part dependent on being able to forecast astronomical events such as, for example, super novae, but not only that, but also on being able to predict or map the probable paths of interferences of the cosmic rays generated by those events. Suddenly, if Svensmark turns out to be right, a whole other layer of confounding complexities superimposes itself on an already incredibly complex system of energy redistributions. At this point, though we actually would have arrived at a better understanding of the what and how of weather and climate, forecasting climate on a scale measured in years would become what perhaps it currently is and will forever remain, little more than the occult reading of signs and auguries.

    If experiments are being conducted to better determine the role of cosmic rays in cloud formation, it is clear that ‘climate science’ is not at an end or complete, and it cannot possibly be stated with any high degree of confidence as yet that, in the absence of anthropogenic CO2, the mean global temperature of our planet would not have increased by 0.85ºC over the last few hundred years.

    On the issue of CO2, the science, it seems to me, is not yet as ‘conclusive’ as many of us currently believe.


  3. Lots of food for thought here. The belief that burning massive amounts of fossil fuels produces increased CO2 concentrations is just a hypothesis, as you point out. So is the theory of evolution. At this point, it’s virtually impossible to prove either of them.

    At the same time it makes intuitive sense that massively disrupting the carbon cycle by burning off tons of fossil fuels is a likely cause of rapidly increasing CO2 concentrations. So perhaps we would be more accurate to call it “common sense,” rather than science. In my mind, the consequences of continuing to increase CO2 concentrations are so dire (we’re really under most immediate threat from ocean acidification and the total depletion of global fish stocks – resulting in slow starvation of billions of people who rely on seafood as their major source of protein) that it would seem prudent to reduce our reliance on fossil fuels.

    It’s also a social justice issue. With growing fossil fuel scarcity, we are rapidly reaching a point where only rich people living in rich countries will be able to afford fossil-fuel based energy. If we can persuade governments to subsidize renewable energy and energy efficiency measures, rather than big coal and big oil, we can increase the availability of cheap energy to the poor.

    I’m reading more an more stories of elderly people who can no longer afford to heat their homes in the winter and who are dying of exposure. I find this extremely concerning.


    • Yes, I completely agree: climate and environmental disruptions are first and foremost social justice issues, and that’s where the focus of the discussion and action should be. Renewable sources of energy over both fossil and nuclear options — by all means.

      The waste of cheap and portable non-renewable energy in the so called developed nations is simply mind boggling: hundreds of millions of vehicles idling away in needless traffic congestion, year in and year out, but for a lack of decent public transit, all in the name of personal convenience; all that motive energy being utterly wasted when instead it might have been put to real use creating systems of efficient production and distribution for millions around the globe who yet lack these and consequently continue to lead difficult lives of bare subsistence; all the energy being wasted in the production of useless, superfluous junk that we call consumer goods and that in their production and consumption as disposables degrade our world, junk that serve the joy of no one, really, since people are either too busy trying to make ends meet, sitting in traffic, or unemployed and simply unable to afford them. The disparity is simply insane, when you mentally juxtapose all of the crying need in the world to the extravagant dissipations of the consumer culture of the developed nations. And then what of the resources wasted in making war merely to keep the party going?

      So I’m inclined to regard the CO2 issue as a kind of distraction, given that it actually appears that we do not know what disasters, if any, it actually portends. Rather, I would insist on the lack of an intelligent, rational and just apportioning of resources, both intellectual and material, as the real crisis of our times, real in the sense that this is something about which we really could do something about and that would yield predictable and tangible improvements in the lives of the many.


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