Plows, Plagues, and Petroleum

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

With a bew afterword by the author William F. Ruddiman
Copyright Date: 2005
Pages: 240
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    Plows, Plagues, and Petroleum
    Book Description:

    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 Petroleumhas 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 Petroleumis 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.

    eISBN: 978-1-4008-3473-0
    Subjects: Physics, General Science, Environmental Science

Table of Contents

  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-viii)
    (pp. ix-xii)
    (pp. xiii-xiv)
  5. Part One What Has Controlled Earth’s Climate?
      (pp. 5-12)

      Most scientists accept the view that human effects on global climate began during the 1800s and have grown steadily since that time. The evidence supporting this view looks quite solid: two greenhouse gases (carbon dioxide, or CO₂, and methane, or CH₄) that are produced both in nature and by humans began unusual rises like the pattern shown in figure 1.1A. Both the rate of change and the high levels attained in the last 100 to 200 years exceed anything observed in the earlier record of changes from ancient air bubbles preserved in ice cores. Because greenhouse gases cause Earth’s climate...

  6. Part Two Nature in Control
      (pp. 17-24)

      Somewhere in East Africa, buried under a thin layer of soil for protection from curious eco-tourists, lie fossilized footprints 3.6 million years old. Soon after a long-ago volcanic eruption, two adult creatures walked across a bed of cooled and rain-moistened volcanic ash, leaving the marks of their feet. Occasionally protruding outside one of the two sets of footprints are extra toe marks, as if a large child was also part of the group, walking along and placing its feet inside the marks made by one of the adults, but occasionally missing the target by a little. Later, the ash hardened...

      (pp. 25-34)

      The realization that small changes in Earth’s orbit might have regular and predictable affects on climate originated just over a century and a half ago. It came about from a convergence of knowledge in two very different disciplines: the still-young science of geology and the somewhat older field of astronomy.

      In the middle 1800s geologists first proposed that great, mile-high ice sheets had existed in large areas of the Northern Hemisphere and had disappeared in the not-too-distant past. These great masses of ice were called “sheets” because of their dimensions: thousands of miles in length and width and a mile...

      (pp. 35-45)

      Imagine standing on a tropical island in the Pacific, one of those coral atolls that barely rises high enough above sea level to avoid being inundated by passing typhoons. Now imagine standing in that exact same spot 20,000 years ago. What would be different? The waves would still be crashing against the edges of that same island, but now some 375 feet below the place you stand. The difference would be the result of water taken from the ocean and stored in ice sheets.

      After almost 40 years’ study of past climates, nothing amazes me more than the fact that...

      (pp. 46-54)

      One of the bleakest places on Earth today is hyperarid Sudan, south of Egypt. Dry winds blow sheets and dunes of sand across the landscape, and almost nothing lives there. But satellite photos and images from heat-sensing devices show subsurface traces of streams and rivers that once flowed eastward to join the Nile River in its northward course from well-watered source areas in the highlands of East Africa. Once, this desert area was green, with broad grasslands and tree-lined waterways inhabited by crocodiles, hippopotamus, ostriches, and rhinoceros. Their bones are found in dried-up stream sediments now covered by a thin...

      (pp. 55-60)

      In almost 2.5 million years, hominids had moved only slightly beyond the most primitive level of Stone Age life, adding control of fire and gradually more sophisticated stone tools to their meager repertoire of skills (table 6.1). But once our species appeared, 150,000 to 100,000 years ago, the pace of change quickened, at least by comparison to the nearly undetectable tempo of previous times. By 50,000 years ago, we see the first real evidence of human creative potential emerging in the artistic and aesthetic expression of people who were like us both in physical respects and mental capabilities. They painted...

  7. Part Three Humans Begin to Take Control
      (pp. 65-75)

      Agriculture originated independently in several regions within the last 12,000 years. The two earliest developments, in the Fertile Crescent region of Mesopotamia at the eastern end of the Mediterranean and in the Yellow River Valley in northern China (fig. 7.1), were to have the largest impact on early civilization. Agricultural discoveries began thousands of years later in other regions, including the Central American lowlands, the high terrain around the Peruvian Andes, and the tropics of Africa and New Guinea. The evidence that agriculture developed independently in these areas rests in part on their geographic separation but mainly on the fact...

      (pp. 76-83)

      Several years ago, just as I was about to retire from the Department of Environmental Sciences at the University of Virginia, I noticed something that didn’t make sense. The methane concentration in the atmosphere during the last 5,000 years had risen, when everything I knew about the climate system told me that it should have fallen.

      My expectation that the methane concentration should have been dropping came directly from John Kutzbach’s theory of the orbital control of monsoons (chapter 5). Summertime solar radiation in the northern tropics reached the most recent of its many 22,000-year peaks nearly 11,000 years ago...

    • Chapter Nine TAKING CONTROL OF CO₂
      (pp. 84-94)

      Convinced that humans had taken control of the atmospheric methane trend by 5,000 years ago, I began to wonder if we might have had a significant effect on carbon dioxide millennia ago. Because CO₂ is a more abundant greenhouse gas than methane, and its effects on climate are generally larger, this question was potentially more important than the methane story, but for a while I resisted pursuing it. One reason for the delay was that CO₂ changes are more difficult to interpret than those of methane. While natural variations in methane are controlled mainly by growth and shrinkage of wetlands...

      (pp. 95-105)

      The evidence seemed clear: human activities linked to farming had taken control of the trends of two major greenhouse gases thousands of years ago, forcing their concentrations to rise when nature would have driven them lower. The net impact of humans through time (fig. 10.1) was a long slow rise in greenhouse-gas concentrations prior to the industrial era, and then much more rapid increases during the last 200 years of industrialization.

      Scientists use a convenient standard to evaluate the climatic impact of greenhouse gases: the amount by which Earth’s climate would warm or cool if the CO₂ concentration were either...

      (pp. 106-114)

      Most new scientific ideas follow a typical sequence. After the “thesis” (publication of the new hypothesis) comes the “antithesis” (evaluation and criticism by the scientific community), and later, for those hypotheses that survive close scrutiny, the “synthesis” (refining or reshaping of the hypothesis into a form that addresses the criticisms and satisfies a wider range of observations). At this point, usually years later, the hypothesis may come to be called a “theory.”

      In the case of my hypothesis, the thesis stage occurred the first week of December 2003, when my paper on early human impacts on climate was published in...

  8. Part Four Disease Enters the Picture
    • Chapter Twelve BUT WHAT ABOUT THOSE CO₂ “WIGGLES”?
      (pp. 119-126)

      Most of the Antarctic ice sheet is a high polar desert receiving no more than an inch or two of snowfall each year, the polar equivalent of the arid core of the Sahara. Ice cores from such locations cannot capture the detail needed to reveal the short-term variations in CO₂ and other gas and solid constituents that occur over centuries or decades. But along the lower margins of the ice sheet, snowfall is heavier, and in favorably sheltered sites it is blown into thicker piles by strong winds. In these places, more detailed records can be recovered. Two such locations...

      (pp. 127-138)

      Historians have long sensed that the last centuries of the Roman era, and those that followed, were something of a reversal in the “onward and upward” march of human progress typical of previous centuries, at least in Europe. The Romans had for a while achieved a level of engineering technology and general prosperity that would not be repeated again in most of the West for over a millennium. Aqueducts brought to their cities fresh water of a quality not equaled until less than 200 years ago in London or Paris. The aqueducts, as well as baths and public structures not...

    • Chapter Fourteen PANDEMICS, CO₂, AND CLIMATE
      (pp. 139-146)

      The correlation between pandemics and drops in atmospheric CO₂ concentrations was suggestive, but what was the connection? How could plague and other diseases cause the drops in CO₂? Part of the answer to these questions comes from historical records summarized in chapter 13. These records document abandonment of farms and farm villages on a massive scale during and after all three major pandemics. In the wake of the European plagues, abandoned farms are described as having gone to waste or ruin. Those words bring to mind doors flapping in the breeze, roofs sagging and collapsing in upon houses and barns,...

  9. Part Five Humans in Control
      (pp. 151-158)

      Readers with a sharp eye may have been puzzled by a part of chapter 10 that seemed contradictory. Figure 10.1 showed that the relatively modest rise of greenhouse gases estimated to have been caused by humans before the Industrial Revolution (40 parts per million for CO₂ and 250 parts per billion for methane) led to a relatively large rise in global temperature (0.8°C), while the larger industrial-era rise in gases (now almost 100 parts per million for CO₂ and 1,000 parts per billion for methane) seem to have resulted in a global temperature increase of only 0.6°C. Although the relative...

      (pp. 159-168)

      The size of the future greenhouse warming hinges mainly on two issues: (1) How high will the concentrations of CO₂ and equivalent greenhouse gases rise because of human activities? (2) How sensitive is the climate system to those increases? The answers to both of these questions have significant uncertainties attached.

      It took millions of years for natural processes to store three carbon-based energy sources in Earth’s sedimentary rocks. The carbon stored in coal originated in vegetation that rotted in oxygen-deficient swamp waters on low-lying continental areas. The carbon stored in oil and natural gas came from the organic remains of...

      (pp. 169-174)

      The role of humans in Earth’s climatic history falls into four phases (fig. 17.1).

      Until 8,000 years ago, nature was in control. Even though our remote prehuman precursors had been present on Earth for several million years, nature alone drove climate change. Even when our fully human ancestors appeared sometime after 150,000 years ago, our impact on the global landscape was still trivial. People used “firesticks” to burn grasslands or forested areas in order to drive game or provide open areas to attract game and permit the growth of berries and other natural sources of food. Some of these early...

  10. Epilogue
      (pp. 179-189)

      The future global warming will be large, but will it be bad or good? In terms of its effects on people, it depends. It depends on such things as who you are, where you live, what you do for a living, your ethical and aesthetic values, and your financial and economic status. Because these considerations lead to different value judgments, this question has no single answer.

      Most climate scientists, aware of the limits of scientific knowledge and wary of complex value judgments, attempt to balance the facts and form their own conclusions. But these scientists are not the people the...

    • Chapter Nineteen CONSUMING EARTH’S GIFTS
      (pp. 190-194)

      Even though I have made the case that future climate change is likely to be large (chapter 16), I do not rank the oncoming global warming as the greatest environmental problem of our time. Other environmental issues seem to me far more immediate and pressing, and in the future I suspect our concerns will focus heavily on the eventual depletion of key resources.

      One theme of this book is that humankind has been steadily transforming Earth’s surface for some 8,000 years, initially in Eurasia and later on all continents. Initially, we caused these transformations by clearing land for farming; later,...

    (pp. 195-214)

    Five years have passed since I wrotePlows, Plagues, and Petroleum(first published in 2005), and this new Princeton Science Library edition gives me an opportunity to look back on the way the science covered in the book has evolved. Because parts 1 and 2 provided fundamental background information, little has changed regarding the issues they discussed. Part 5 largely dealt with modern and future climate, and the most noteworthy shift in the last five years has been the development of an even stronger consensus that humans are the primary explanation for the approximately 0.7˚C global warming during the last...

    (pp. 215-218)
    (pp. 219-222)
  14. INDEX
    (pp. 223-226)