Anthropocene

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The term Anthropocene is used by some scientists to describe the most recent period in the Earth's history, starting in the 18th century when the activities of the human race first began to have a significant global impact on the Earth's climate and ecosystems. The term was coined in 2000 by the Nobel Prize winning scientist Paul Crutzen, who regards the influence of mankind on the Earth in recent centuries as so significant as to constitute a new geological era.

While much of the environmental change presently occurring on Earth is a direct consequence of the industrial revolution, it can be argued that the Anthropocene actually began approximately 10,000 years ago with the termination of the last ice age. At this point, humans were dispersed across all of the continents (bar Antarctica), and the neolithic revolution was ongoing. This introduced agriculture and animal husbandry to supplement or replace hunter-gatherer subsistence, and was followed by a wave of extinctions, beginning with large mammals, and land birds. This wave was driven by both the direct activity of humans (e.g. hunting) and the indirect consequences of land-use change for agriculture. This period (10,000 years to present) is usually referred to as the Holocene by geologists, and for the majority of it human populations were relatively low and their activities considerably muted relative to that of the last few centuries. Nonetheless, many of the processes currently altering the Earth's environment were still taking place during this period.

One obvious geological signal of human activity is increasing atmospheric carbon dioxide (CO₂) content. During the glacial-interglacial cycles of the past million years, natural processes have varied CO₂ by approximately 100 ppm (from 180 ppm to 280 ppm). As of 2005, anthropogenic net emissions of CO₂ have increased its atmospheric concentration by a comparable amount from 280 ppm (Holocene or pre-industrial "equilibrium") to more than 380 ppm. This signal in the Earth's climate system is especially significant because it is occurring much faster than previous, similar changes. Most of this increase is due to the combustion of fossil fuels such as coal, oil and gas, although smaller fractions are the result of cement production and land-use changes (e.g. deforestation).

William Ruddiman [1] [2] [3] claims that ancient forest clearance and rice paddies increased CO₂ and methane levels starting 8000 years ago; Ruddiman's work has in turn been challenged by Schmidt et al., who say that there is no need for a significant anthropogenic influence on the methane record.

[edit] References

Crutzen, P. J., and E. F. Stoermer. 2000. The "Anthropocene". Global Change Newsletter. 41: 12-13.
A note on the relationship between ice core methane concentrations and insolation, Schmidt, GA, Shindel, DT and Harder, S; GRL v31 L23206, 16 December 2004.
The anthropogenic greenhouse era began thousands of years ago, Ruddiman WF; Climatic Change, 61 (3): 261-293 Dec 2003
A test of the overdue-glaciation hypothesis, William F. Ruddiman, Stephen J. Vavrus, John E. Kutzbach, Quaternary Science Reviews 24 (2005) 11
William F. Ruddiman (2005), Plows, Plagues, and Petroleum:How Humans Took Control of Climate, Princeton University Press