Blake Earle
“How Did Humans First Alter
Climate?” from Scientific American, March 2005
Plows, Plagues, and Petroleum:
How Humans Took Control of
Climate
Ruddiman, 2001
Ruddiman, 2007
Ruddiman, 2007
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Over the past 400,000 years the Milankovitch
Cycles have controlled CO2 and methane
concentrations.
Methane fluctuates at the 22,000 year tempo
(precession) as the Northern Hemisphere
swings closer towards the sun and receives a
boost in radiation, leading to greater
decomposition of plant matter in wetlands.
Ruddiman, 2005
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In southern Asia increased solar radiation
strengthens monsoon cycles that flood areas
that would otherwise remain dry.
In far northern Asia and Europe warmer
summers thaw boreal wetlands for longer
periods.
In both areas this process allows more
vegetation to grow, decompose, and emit
methane at a predictable 22,000 year tempo.
Ruddiman, 2005
Ruddiman, 2007
Ruddiman, 2007
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Other investigators have suggested the
following to explain these oddities:
 Expansion of wetlands in Arctic regions
 CO2 rise has been attributed to natural losses of
vegetation rich in carbon
 Changes in ocean chemistry
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However, Dr. Ruddiman was not content with
these explanations, citing the fact that the
parameters for climate change have been the
same in all other inter-glacial periods.
Ruddiman, 2005
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Agriculture originated approximately 11,000
years ago in the Fertile Crescent, shortly after
in China and several thousand years later in
the Americas.
By 2,000 years ago every food crop eaten
today was being grown some where in the
world.
Various agricultural activity produce both CH4
and CO2
Ruddiman, 2005
Ruddiman, 2007
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One common practice tied to farming was
deforestation which became popular in China
and Europe approximately 8,000 years ago.
Fallen trees were either burned or left to rot,
both processes emit CO2 to the atmosphere.
Ruddiman, 2005
Ruddiman, 2007
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Around 5,000 years ago farmer in southern
China began to flood lowland areas near
rivers in order to propagate wet-adapted
strains of rice.
By 3,000 years ago this procedure spread
south into Indochina and west towards the
Ganges River Valley.
This process is a major produce of methane.
Ruddiman, 2005
Ruddiman, 2007
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Stephen J. Vavrus and John E. Kutzbach along
with Dr. Ruddiman used a climate model to
predict modern-day temperature in the absence
of these agriculture related greenhouse gas
emissions.
The result showed a difference of two degrees
Celsius.
Other researchers have previously shown that
parts of northeastern Canada might be covered
with ice if world temperature was a mere 1.5
degrees Celsius cooler.
Ruddiman, 2005
Ruddiman, 2007
Ruddiman, 2007
“My findings add a new wrinkle to each
scenario. If anything, such forecasts of an
“impending” ice age were actually
understated: new ice sheets should have
begun to grow several millennia ago. The ice
failed to grow because human-induced global
warming actually began far earlier than
previously through—well before the industrial
era.” ~William F. Ruddiman
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Some have suggested that the anomaly Ruddiman
observed is unfounded because he did not
investigated an interglacial 400,000 years ago in
which solar radiation trends were more like those of
today.
Other doubt Ruddiman’s suggestion that the 40-ppm
CO2 anomaly was caused by 200 billion tons of
carbon produced by human activity. They have
suggested that between 550-700 billion tons of carbon
would have been needed, and since humans could not
have produced this much carbon in the past few
thousand years, humans are not the cause of the
anomaly in carbon.
Ruddiman, 2007
Ruddiman, William F. Earth’s Climate. New York: W.H. Freeman, 2001.
Ruddiman, William F. “How Did Humans First Alter Global Climate?” Scientific American March
2005.
Ruddiman, William F. Plows, Plagues, and Petroleum: How Humans Took Control of Climate.
Princeton: Princeton UP, 2007.
Ruddiman, William F. Orbital insolation, ice volume, and greenhouse gases.
http://cfa-www.harvard.edu/~wsoon/Liu03-d/ODP1012-d/Ruddiman03.pdf
Ruddiman, William F. Environmental Sciences Department.
http://www.evsc.virginia.edu/faculty/people/ruddiman.shtml
I couldn’t
Earth Observatory Library Milutin Milankovitch.
have
http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/
done it
better
myself.