From Wikipedia, the free encyclopedia

Jump to: navigation, search
Holocene epoch
Preboreal (10 ka – 9 ka),
Boreal (9 ka – 8 ka),
Atlantic (8 ka5 ka),
Subboreal (5 ka2.5 ka)
Subatlantic (2.5 ka – present)

The term Anthropocene is used by some scientists to describe the most recent period in the Earth's history. It has no precise start date, but may be considered to start in the late 18th century when the activities of humans first began to have a significant global impact on the Earth's climate and ecosystems. This date coincides with James Watt's invention of the steam engine in 1784.[1] The term was coined in 2000 by the Nobel Prize winning atmospheric chemist Paul Crutzen, who regards the influence of human behavior on the Earth in recent centuries as so significant as to constitute a new geological era.

Use of this concept as an official geological concept gained new support in early 2008, with publication of two new papers supporting this idea.[2]

[edit] Definition of era

While much of the environmental change presently occurring on Earth is a direct consequence of the industrial revolution, William Ruddiman has argued that the Anthropocene actually began approximately 8,000 years ago with the growth of farming. 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 already taking place during this period.

[edit] Nature of human effects

The Earth at night, a simulated night-time image of the world during the anthropocene.

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 2006, 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 383 ppm. This signal in the Earth's climate system is especially significant because it is occurring much faster, and to an enormously greater extent, 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 claims that the anthropocene as defined by significant human impact on greenhouse gas emissions began not in the industrial era, but 8,000 years ago, as ancient farmers cleared forests to grow crops, the early anthropocene hypothesis.[3][4][5] Ruddiman's work has in turn been challenged on the grounds that comparison with an earlier interglaciation ("Stage 11", around 400,000 years ago) suggest that 16,000 more years must elapse before the current Holocene interglaciation comes to an end, and that thus the early anthropogenic hypothesis is invalid. But Ruddiman argues that this results from an invalid alignment of recent insolation maxima with insolation minima from the past, among other irregularities which invalidate the criticism.

[edit] Etymology

Anthropocene is a neologism coined in 2000 by the Nobel Prize winning scientist Paul Crutzen by analogy with the word "Holocene." The Greek roots are "anthropo-" meaning "human" and "-cene" meaning "new." Crutzen has explained, "I was at a conference where someone said something about the Holocene. I suddenly thought this was wrong. The world has changed too much. So I said: 'No, we are in the Anthropocene.' I just made up the word on the spur of the moment. Everyone was shocked. But it seems to have stuck."[6] Crutzen first used it in print in a 2000 newsletter of the International Geosphere-Biosphere Programme (IGBP), No.41. In 2008, Zalasiewicz suggested in GSA Today that an anthropocene epoch is now appropriate.[2]

A similar term was apparently coined by Andrew Revkin in his 1992 book Global Warming: Understanding the Forecast, in which he wrote that "we are entering an age that might someday be referred to as, say, the Anthrocene. After all, it is a geological age of our own making." The word Anthropocene is generally regarded as being a more suitable technical term.[7]

[edit] References Cited

  1. ^ Crutzen, P. J., and E. F. Stoermer, "The 'Anthropocene'". Global Change Newsletter 41, pp. 17-18, 2000.
  2. ^ a b Zalasiewicz, Jan; et al (February 2008). "Are we now living in the Anthropocene?". GSA Today (Geological Society of America) 18 (2): 4–8. doi:10.1130/GSAT01802A.1. 
  3. ^ Mason, Betsy (2003). "Man has been changing climate for 8,000 years". Nature. doi:10.1038/news031208-7. 
  4. ^ Adler, Robert (2003-12-11). "Early farmers warmed Earth's climate". New Scientist. Retrieved on 2008-02-04. 
  5. ^ Ruddiman, William F. (2003). "The Anthropogenic Greenhouse Era Began Thousands of Years Ago". Climatic Change 61 (3): 261-293. doi:10.1023/B:CLIM.0000004577.17928.fa. 
  6. ^ Pearce, Fred, With Speed and Violence, p. 21, 2007. ISBN 978-0-8070-8576-9
  7. ^ Revkin, Andrew, The "Anthrocene" era — of a human-shaped Earth, 2007.

[edit] Other References

  • Schmidt, G. A., D. T. Shindel and S. Harder, "A note on the relationship between ice core methane concentrations and insolation", Geophysical Research Letters, Vol. 31, Issue 23, CiteID L23206, 16 December 2004.
  • Ruddiman, William F., "The anthropogenic greenhouse era began thousands of years ago", Climatic Change, No. 61 (3). pp. 261-293, Dec 2003.
  • Ruddiman, William F., Stephen J. Vavrus and John E. Kutzbach, "A test of the overdue-glaciation hypothesis", Quaternary Science Reviews 24, p. 11, 2005.
  • Ruddiman, William F., Plows, Plagues, and Petroleum: How Humans Took Control of Climate, Princeton University Press, 2005.

[edit] See also

[edit] External links

Personal tools