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.

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