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The
Anthropocene
In geological terms time is divided into Eras which
are divided into Periods. The periods
are divided into Epochs.
Currently we are in the Cainozoic Era. This started when the dinosaurs died
out. We are in the Quaternary
Period. This is the period of the Ice Ages. Our current Epoch is the Holocene. This is a warm Epoch in the Ice Age
period. The Holocene started about 8000
years ago.
Holocene means recent whole.
Anthropocene
In 2000, Professor Paul Crutzen (The 1995 Nobel Prize
Winner for Chemistry) proposed that we are now in a new geological Epoch. That is that the effects of Human actions on
the world are so pervasive that we have changed things so much that the present
Epoch should be called the Anthropocene.
Past Eras, Epochs and Ages are defined by the
geological record. There is no doubt
that there are several things that will define our present Epoch in the
geological record of the future.
Start of the
Anthropocene
Professor Crutzen proposed that the Anthropocene start
date should be in the late 18th century. However, he acknowledged that some people
would want to set it much earlier.
Bill
Ruddiman
Professor William F Ruddiman PhD is Professor Emeritus
of Environmental Sciences at the University
of Virginia. He has suggested that the Anthropocene Epoch
actually began approximately 8000 years ago.
This was when agriculture began in many places of the world. The population of the world was only about
5,000,000 people. Not all of these were
farmers, but the hunters and gatherers were also using fire both for hunting
and for clearing land to allow green grass to grow and attract animals.
Agricultural practices lead to the release of
considerable amounts of carbon dioxide. These practices included burning the existing
vegetation before planting crops. Sometimes the vegetation burned was
forest. The geological record starts to
show anomalously high carbon dioxide levels from 8000 years ago.
Some practices such as wet agriculture; growing crops
like Rice and Taro release large amounts of Methane. The geological record starts to show higher
than expected methane levels from 5000 years ago. By this time the population of the world had
grown to about 14,000,000 people.
Although I am not aware that professor Ruddiman took them
into account, we can add the contribution of non agricultural peoples who used
fire for hunting, and also the weirs constructed by the Australian Aboriginal
people to make seasonal swamps to grow eels in.
Little Ice
Age
This is a period in history very roughly from the 16th
to the 19th centuries. Professor
Ruddiman has correlated the dips in global temperature with dips in carbon
dioxide concentration. These in turn
appear to be correlated with the drops in world population caused by the Black
Death. When a lot of people died,
agricultural land was abandoned and forests grew back, removing carbon dioxide
from the atmosphere.
Ice Age
Professor Ruddiman’s calculations suggest that without
this Anthropomorphic Global Warming we would already be in an ice age. The release of greenhouse gasses by Humans
has been just enough to stave off the start of an ice age.
Sun Spots
When the Sun has more Sun Spots the Earth seems to
warm up. This seems backwards, but the
correlation has been found. Recently we
have been going through an unusually quiet time for Sun Spots.
The ten years from 2000 to 2009 was the hottest decade
ever recorded, but it was not as hot as was predicted. It seems likely that the lack of Sun Spots
was responsible for this apparent slowing of the rate of Global Warming. During that decade, the level of carbon
dioxide continued to climb. This means
that when more vigorous Sun Spot activity is resumed the Earth’s temperature
could go up rapidly.
Out of Control
In the early parts of the Anthropocene our green house
emissions helped keep the Earth’s temperature fairly constant.
Now with the world population up to nearly
7,000,000,000, and "population growth" still high, as well as an average increase
in per capita green house gas emission, the Earth’s temperature could become
much higher than is good for us, or for the currently existing animals and
plants.
Sources
Paul Josef Crutzen’s original paper.
http://geology.about.com/gi/o.htm?zi=1/XJ&zTi=1&sdn=geology&cdn=education&tm=948&f=10&su=p897.9.336.ip_&tt=2&bt=1&bts=1&zu=http%3A//www.mpch-mainz.mpg.de/~air/anthropocene/Text.html
Professor
Crutzen’s home page:
http://www.mpch-mainz.mpg.de/~air/crutzen/
Bill Ruddiman:
http://www.evsc.virginia.edu/faculty/ruddiman-william-f/
The
Anthropogenic Greenhouse Era Began Thousands of Years Ago:
The
Weather Makers by Tim Flannery
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