Research Question And Approach Article Review Example

Ruddiman’s article “The Anthropogenic Greenhouse Era Began Thousands of Years Ago” is an intriguing take on the global climatic impact that humanity is believed to be capable of producing. The article begins by acknowledging that generally the Anthropocene is not considered to have started until 1800 AD at the beginning of the industrial age. However, Ruddiman asks the question, “Did human created emissions of methane and carbon dioxide result in an earlier start to the anthropogenic era and overall climate warming than current estimates dictate?”’ He approaches the solution through a detailed examination of scholarly articles and data from geologic, climatic, and anthropological sources. Through his research, Ruddiman posits a hypothesis that in fact human impact on the climate can be traced back 8,000 years BP and is the main factor in a warming climate that contradicts modeling which predicted a cooler climate over this same time period.

Main Results

Ruddiman discusses in detail the measurements of methane (CH4) and carbon dioxide (CO2) that have been recorded in the scientific literature and which reflect the trends in these greenhouse gas levels in the atmosphere over the past millennia. He makes a compelling case based on the anticipated levels of these gases that would be expected due to changes in Earth’s orbit on its axis and the resulting decrease in summer insolation. Because the Earth wavers on its axis, the amount of seasonal sunlight and corresponding radiation each hemisphere receives actually differs over time. These orbital and insolation changes should have resulted in a cooler climate and advancing glaciation several thousand years ago. However, not only did this not occur, but global temperatures actually increased over the same time period. Figures 1b and 9 are particularly illustrative of this point. They demonstrate that while the summer insolation decreased, methane levels increased over the same time period and not only did glaciation not occur, but the temperatures were significantly higher than the “Glaciation threshold”. This suggests that not only did the Holocene insolation not result in glaciation, but human greenhouse gases caused a warming that more than compensated for the cooling insolation effect.
Ruddiman acknowledges arguments for other non-human causes for the increase in global concentrations of these gases. It has been argued that the rise in methane and carbon dioxide levels during this time period could be due to other factors such as orbital-scale forcing from naturally occurring biomass losses or ocean acidification. Ruddiman argues against both cases citing the fact that for these hypothesis to hold true, they would have to be reflected in previous periods of interglaciations. However, the data does not support this and sets the Holocene apart as an anomaly. He states, “neither of the two published explanations of the late-Holocene CO2 increase is tenable. Both face a problem common to any explanation based on natural processes: the lack of substantial differences in orbital-scale forcing during the Holocene compared to the three previous interglaciations” (Ruddiman 271). For Ruddiman, the explanation for this anomaly is increased human activity beginning in 8,000 BP.

Conclusion

Based upon the results of his research, Ruddiman concludes that the increased temperatures over the last 8,000 years is in fact resulting from the increased methane and carbon dioxide gases recorded in the atmosphere during this time period. He therefore concludes, that these increased greenhouse gas emissions are an anomaly from the three previous periods of interglaciation and that the only explanation that matches the data accurately is that these emissions are the result of increased human activity in the form of expanding agriculture and deforestation. Further evidence in support of his hypothesis comes from what one would expect would be evidence to the contrary. The Little Ice Age, occurring between 1300 and 1900 AD during which global temperatures and levels of methane and carbon dioxide decreased, would seem to suggest that humans were not having a significant impact on the climate. However, Ruddiman points to the occurrence of the bubonic plague corresponding with the beginning of the fourteenth century. He concludes that the decimation of that plague, which estimates state killed one fourth to one third of the entire European population, resulted in a temporary lull in human activity and even the sequestration of carbon as farms were re-absorbed by forests. He states, “if the CO2 records from Taylor and Law Domes are a more accurate measure of past CO2 changes than other ice-core record from Antarctica, then plague-induced reforestation events are strongly implicated in the amplitude and timing of the 10-ppm drops in CO2” (290). This temporary reduction in human population and therefore activity is responsible for the decline in emissions that followed and the corresponding cooling of the climate.

Opinion

Ruddiman makes a strong argument for his hypothesis. His data analysis appears solid and his points are well reasoned. I am apt to agree with him on most of his conclusions. In particular, it does not seem far-fetched to assume the potential for global impact by human populations even as far back as 8,000 years ago. Comparable research of Paleolithic humans suggests that they had significant impact on other aspects of the global environment including the probable extinction of the mammoth due to over hunting as well as other species. Most compelling were Ruddiman’s comparisons of the Holocene data to previous periods of interglaciations. The cyclical nature of these previous interglacial periods and how the Holocene differs significantly stressed the anomaly factor for me and definitely suggests that something different occurred between 8,000 and 6,000 years ago that led to higher greenhouse gas levels and temperatures. My one criticism of Ruddiman, however, is in the exploration of other potential explanations for the anomaly. While he does explore two alternative hypothesis that he then soundly rejects, it seems that for a topic of this breadth the number of alternative explanations would be much more expansive. For example, I’ve read about the impact of Earth’s elliptical orbit on historical climate change and how that has been posited as a potential reason for the Little Ice Age because the Earth was farther away from the sun in its orbit for extended periods. Other than this one criticism, I found the article to be a fascinating exploration of our human ancestors’ potential to impact the environment at a global scale.

Work Cited

Ruddiman, William F. “The Anthropogenic Greenhouse Era Began Thousands of Years Ago.” Climate Change 61 (2003):261-293