Anthropocene

New geological ages are characterized by changes in global environmental conditions and large scale shifts in types of species. Recently Earth has entered into a new geological age: The Anthropocene, from anthropo = man and cene = new [geological age]. Humans are now changing the world on a global scale and ushering in the new era in geologic time. (reference)

The term was coined in 2000by the Nobel Prize winning Dutch atmospheric scientist Paul Crutzen to describe the past two centuries of our planet's evolution. "I was at a conference where someone said something about the Holocene, the long period of relatively stable climate since the end of the last ice age. I suddenly thought that 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." Fred Pearce in With Speed and Violence.

To assign a more specific date to the onset of the Anthropocene seems somewhat arbitrary, but the latter part of the 18th century seems to be appropriate since this is when the global effects of human activities have become clearly noticeable. This is the period when data retrieved from glacial ice cores show the beginning of a growth in the atmospheric concentrations of several greenhouse gases, in particular carbon dioxide and methane. Such a starting date also coincides with James Watt'sinvention of the steam engine in 1784. About at that time, biotic assemblages in most lakes began to show large changes. The expansion of mankind, both in numbers and per capita exploitation of Earth's resources has been astounding. To give a few examples: (reference)

• During the past 3 centuries human population increased tenfold to 6000 million, accompanied e.g. by a growth in cattle population to 1400 million or about one cow per average size family.
• Urbanisation has even increased tenfold in the past century. In a few generations mankind is exhausting the fossil fuels that were generated over several hundred million years.
• The release of sulfur dioxide, globally about 160 gigatons/year to the atmosphere by coal and oil burning, is at least two times larger than the sum of all natural emissions, occurring mainly as marine dimethyl-sulfide from the oceans.
• 30-50% of the land surface has been transformed by human action; more nitrogen is now fixed synthetically and applied as fertilizers in agriculture than fixed naturally in all terrestrial ecosystems.
• The escape into the atmosphere of nitrous oxide (NO) from fossil fuel and biomass combustion likewise is larger than the natural inputs, giving rise to photochemical ozone ('smog') formation in extensive regions of the world.
• More than half of all accessible fresh water is used by mankind; human activity has increased the species extinction rate by thousand to ten thousand fold in the tropical rain forests.
• Several climatically important greenhouse gases have substantially increased in the atmosphere: carbon dioxide by more than 30% and methane by even more than 100%.

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