Plows, Plagues, and Petroleum: William

Plows, Plagues, and Petroleum: William F. Ruddiman's Evidence for Long-Term Anthropogenic Climate Change

A family huddles together for warmth in a the center of an especially thin-walled thatch hut, the sputtering fire little warmth to combat the wind that finds its cold and hungry way into every possible corner of the one-roomed home. Wrapped in a blanket that is woven of coarse, thick wool if they were lucky, or of a thinner and more permeable fabric if times were harder, these human creatures are forced to wait out the cold winter with little else, hoping that what food they had would be enough to last because more would not be easily forthcoming in the harsh landscape outside. There were neighbors of course, and a lord that ostensibly offered cared for his vassals, but these offered no certain protection against the vagaries of the environment and the potential for destruction that it carried with it at the turn of every season, and especially as the days shortened.

Such scenes were common in the Middle Ages, and it is difficult to imagine that the people of Europe -- the majority of whom lived in huts similar to those described rather than large cities or stone castles as is popularly imagined -- were actually having a significant impact on the global environment when it was so obviously and so extensively having an effect on them. Yet according to the claims and considerable evidence presented by William F. Ruddiman in his book, Plows, Plagues, and Petroleum, this is precisely what was occurring at key times throughout human history, and particularly the development of Western civilization.

Ruddiman makes an excellent case for his assertions, citing an abundance of contemporary scientific and historical evidence in a way that presents a unified and comprehensive view of both the human and the global trajectories over the many millennia of their coexistence. His objectivity despite his obvious convictions is also remarkable, and highly compelling -- Ruddiman is careful to maintain that there is no proven link between his assertion, but that the number of mounting coincidences seems to add up in favor of his ultimate conclusions. Presented in such a manner, it is difficult to disagree with Ruddiman, yet doubt does creep in when some of the scientific objections to his arguments and conclusions are raised by other researchers in the field. This paper will examine Ruddiman's arguments in the context of his status and the opposing views that counter certain specific conclusions Ruddiman draws and his conclusions generally, in an effort to build a more comprehensive and a more compelling understanding of these arguments and their merits.

William F. Ruddiman

Though William F. Ruddiman was quickly drawn to a study of the environment, his initial education did not take place in either atmospheric or environmental sciences. Ruddiman was actually trained as marine geologist. His first major research project, however, involved a study of the migration patterns of sea sediments and their relationship to sea surface temperatures. These in turn have, of course, an effect on -- and are influenced by -- global temperature and climate changes, now a long-standing interest of the author (Ruddiman 2010).

Ruddiman has long been an innovator in the study of global warming, approaching the topic from a multitude of scientific angles and disciplines and always receiving consistent praise for his careful consideration and presentation of evidence, even -- and perhaps especially -- when presented in laymen's terms, as in Plows, Plagues, and Petroleum (Bert 2003). His long-standing respect in the scientific research community is marked both by his current position as a semi-retired professor emeritus at the University of Virginia, and by the prestige of his alma mater, Columbia University (Ruddiman 2010). Ruddiman also has several other published books and numerous articles, and has collaborated with many other researchers in varying fields to develop cutting-edge and comprehensive concepts of what is driving global climate change, and what role human beings might be playing -- and possibly should be playing -- in the global environment (Ruddiman 2010).

Plows, Plagues, and Petroleum

The argument that Ruddiman puts forward in his book is relatively simple and straightforward, even if the evidence behind this argument and the research used to obtain that evidence are not. Essentially, Ruddiman maintains that large changes in the human population and in the degrees and extent of human agriculture, as well as other large-scale human activities as civilization "progressed," have led to periods of global warming and cooling in the past (Ruddiman 2005). Greenhouse gases, though newly a household term, are not new byproducts of human activity, and they were having an effect -- according to Ruddiman -- since civilization began.

Ruddiman begins his argument with the development of agriculture approximately eight thousand years ago, during a time when carbon dioxide and methane in the atmosphere should have been decreasing according to the Earth's natural cycles. Instead, Ruddiman observed an increase of these gases as preserved in ice core samples, and he attributes this to the expansion of human society after the development of agriculture (Ruddiman 2005). Any imaginable combustible fuel, from standard gasoline to cow chips and wood, releases carbon and other greenhouse gases into the air, and the expansion of human populations and the establishment of cities, in Ruddiman's view, necessarily led to greater fuel consumptions and greenhouse gas releases from other human activities (Ruddiman 2005). This is the source of the gas increase observed in the ice core, according to Ruddiman, and evidence of humanity's long-term influence on the environment.

Ruddiman does not leave off here, but travels to the Middle Ages and other periods in the development of human history when less savory things than the agricultural revolution occurred. The bubonic plague, for instance, which wiped out possibly as much as two thirds of Europe's population during the 1300s, coincides with a brief downward "wiggle" in the level of greenhouse gases found in the geological records, a fact which Ruddiman denies is coincidental at all. Instead, according to him, hugely suggests that the massive reduction in human population is tied to the reduction in greenhouse gases present in the atmosphere, for the same reasons that population growth caused an increase (Ruddiman 2005).

Ruddiman concludes his text by examining our current and potentially future state, particularly with our use of petroleum and other fossil fuels. Though many of these actually burn far cleaner than older fuels used in the times Ruddiman discusses, the human population is exponentially larger than it was in the Middle Ages and is still growing, and greenhouse gas emissions are significantly higher now than at any other time in human history. Ruddiman insists that this will lead to a warming trend, and doubts that sufficient technological steps will be taken in the near enough future and on a massive enough scale -- if such a thing were even physically possible -- to alter the situation, especially given the continued use of such fuels (Ruddiman 2005). After making such a compelling argument about long-past events and effects of humanity, Ruddiman's warning strikes especially prepared and well-attuned -- and well-informed -- ears.

Opposing Views

Other well-informed ears find something amiss in Ruddiman's arguments, however, and these opposing views are not without their merits. Though the evidence for Ruddiman's arguments is compelling, it is not certain, and is in fact far from what would be considered even scientifically certain. Ruddiman points out what appears to be a strong correlation between human population increases and depletions and levels of greenhouse gases. This does not show a causal effect, nor does it establish a scientific link between the greenhouse gas levels observed and warming trends -- this too is simply another observation of correlation.

There are several other points of contention that other researchers have found with Ruddiman's work. Even those who agree with most of Ruddiman's science disagree with his ultimate conclusions. Gary Shaffer's (2008) relatively recent article in Geophysical Research Letters recommends the controlled use of fossil fuels in order to forestall another glacial period, thus making practical use of the heretofore accidental cause-and-effect relationship Ruddiman posits. Other researchers take direct issue with the science that Ruddiman relies on, rather than the direction towards which he points it. Claussen et al. (2005) researched climate change and atmospheric gas cycles around the same medieval period that Ruddiman uses as one of his examples, and claim that glaciation would have been averted regardless of human population changes due to the Earth's natural cycles.

William Broecker is even more direct in his refutation of many of Ruddiman's conclusions, citing the author of Plows, Plagues, and Petroleum directly in his claim that it is in the orbital eccentricities and patterns of the Earth as it travels around the Sun, as well as patterns in the Sun's own internal cycles, that are responsible for the warming and cooling patterns observed on Earth, rather than the changes in greenhouse gas emissions whether anthropogenic or natural in origin. Many social commentators and scientists still question the very existence of global warming, especially in the face of largely anecdotal and non-scientific evidence such as harsh snow-storms and record low temperatures (McKee 2009). The more political arguments against Ruddiman are more easily dismissed, however.