Mounting evidence suggests early agriculture staved off global cooling

January 18, 2016 by Fariss Samarrai
Ancient agriculture, including early rice farming, may have played a role in delaying the next ice age, according to new research.

A new analysis of ice-core climate data, archeological evidence and ancient pollen samples strongly suggests that agriculture by humans 7,000 years ago likely slowed a natural cooling process of the global climate, playing a role in the relatively warmer climate we experience today.

A study detailing the findings is published online in a recent edition of the journal Reviews of Geophysics, published by the American Geophysical Union.

"Early farming helped keep the planet warm," said William Ruddiman, a University of Virginia scientist and lead author of the study, who specializes in investigating ocean sediment and ice-core records for evidence of climate fluctuations.

A dozen years ago, Ruddiman hypothesized that early humans altered the climate by burning massive areas of forests to clear the way for crops and livestock grazing. The resulting and methane released into the atmosphere had a warming effect that "cancelled most or all of a natural cooling that should have occurred," he said.

That idea, which came to be known as the "early anthropogenic hypothesis" was hotly debated for years by climate scientists, and is still considered debatable by some of these scientists. But in the new paper, Ruddiman and his 11 co-authors from institutions in the United States and Europe say that accumulating evidence in the past few years, particularly from ice-core records dating back to 800,000 years ago, show that an expected cooling period was halted after the advent of large-scale agriculture. Otherwise, they say, the Earth would have entered the early stages of a natural ice age, or glaciation period.

The Earth naturally cycles between cool glacial periods and warmer interglacial periods because of variations in its orbit around the sun. We currently are in an interglacial period, called the Holocene epoch, which began nearly 12,000 years ago.

In 2003, Ruddiman developed his early anthropogenic hypothesis after examining 350,000 years of climate data from ice cores and other sources. He found that during interglacial periods, carbon dioxide and methane levels decreased, cooling the climate and making way for a succeeding glacial period. But, only during the Holocene era, these gas levels rose, coinciding, he said, with the beginning of large-scale agriculture. He attributed the rise to this human activity, which began occurring millennia before the industrial era.

He attributed the rise in to the slash and burn techniques widely used by early farmers to make available large areas of land for crops. Ruddiman found that carbon dioxide levels rose beginning 7,000 years ago, and that methane began rising 5,000 years ago. He said this explains why a cooling trend didn't happen that likely otherwise would have led to a new glacial period.

In the new study, Ruddiman and his colleagues have delved more deeply into the climate record using Antarctic ice-core data, dating back to 800,000 years ago. This use of a deeper historical data set clearly shows, they say, that the Holocene is unlike other in its abundance of carbon dioxide and methane, further implicating the impact of humans.

In the development of his hypothesis, Ruddiman and colleagues have drawn from numerous studies across scientific disciplines: climatology, anthropology, archaeology, paleoecology, and population dynamics, all to better understand how humans may have affected climate beyond the relatively recent industrial revolution and the widespread burning of fossil fuels.

They cite a recent study that also summarized archaeological studies and found that early rice irrigation, which releases methane gas to the atmosphere, explains most of the anomalously high rise in atmospheric methane beginning about 5,000 years ago. A proliferation of livestock farming during that time period also may explain part of the methane increase.

"After 12 years of debate about whether the climate of the last several thousand years has been entirely natural or in considerable part the result of early agriculture, converging evidence from several scientific disciplines points to a major anthropogenic influence," Ruddiman said.

Explore further: Human-made climate change may be suppressing the next ice age (Update)

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Anonym
2.3 / 5 (16) Jan 18, 2016
What was the global human population 7,000 years ago? How did they burn "massive areas" of forest, and how do we know it was humans and not climate change that was the cause of the fires? Seriously, does anyone actually believe this stuff is real?
BartV
2.3 / 5 (19) Jan 18, 2016
Anonym, it is all part of the worldwide "global-warming" movement, made up of people who like to claim that man can indeed have the power change long-term weather, so that they can slap arbitrary restrictions and regulations in controlling the masses in all areas of life.

Of course it is silly, and many serious people don't believe this stuff is real.
Mike_Massen
2.9 / 5 (17) Jan 18, 2016
BartV the uneducated waste of time claims
Anonym, it is all part of the worldwide "global-warming" movement, made up of people who like to claim that man can indeed have the power change long-term weather, so that they can slap arbitrary restrictions and regulations in controlling the masses in all areas of life.
Of course it is silly, and many serious people don't believe this stuff is real
Ignoramus !

You ignore, at the world's peril key Scientific advances:-

https://en.wikipe...transfer
https://en.wikipe..._forcing
http://cbc.arizon.../sim/gh/

Heard of Physics re heat - heard of maths BartV, why are you so inanely ignorant of Science ?
https://en.wikipe...echanics
https://en.wikipe...capacity

Education beyond you ?

Tell us how your god, any and all gods, communicate, anything like lazy power hungry humans who merely make claim to aggrandize ?
NiteSkyGerl
3.2 / 5 (13) Jan 18, 2016
You can't find anything pristine anywhere that humans haven't altered. I guess if you can believe the Sky Daddy mythos you can swallow anything, like some stupid arbitrary religion generated excuse that we're so small and God is so great...

What's small is their intellect and what's great is the challenge. A major population correction wouldn't be bad as the tin foil jobs usually manage to shoot themselves in the foot. Just ask Steve Jobs how dead pseudoscience can kill you.
cgsperling
2.7 / 5 (7) Jan 18, 2016
It seems like +-7000 years would just be noise in the definition of an epoch. Let's peg it at Darwin's birthday, and call it a day.
Torbjorn_Larsson_OM
5 / 5 (5) Jan 19, 2016
The Reviews of Geophysics paper ties in with a recent Nature paper on how pre-industrial carbon levels, an extra 40 ppm compared to earlier ice age with the solar influx, delays the next ice ige. The 40 ppm is exactly the CO2 change that Ruddiman found 2003. [ http://arstechnic...ng-time/ ; http://www.realcl...othesis/ ]
Torbjorn_Larsson_OM
4.3 / 5 (6) Jan 19, 2016
@Anonym: Many estimates gets ~ 5 million humans @ 10 kyrs ago. [ https://en.wikipe...stimates ]

It is argued why agrarian practices increased and all the global forests (except Amazon) were burned independently from 6-7 centra, but it is believed a shared tool set and the population density combined with migration set that off. The same thing happened when there was a global (except uninhabited Americas) stone tool culture change ~65 kyrs ago.

Yes, scientists from climate science to archaeology and geosciences can't reject this, because although there are remaining open points (re how much forest was cut down) the evidence is there and it is correlated. Mind, scientists don't 'believe', they either know or don't know. Opinion (belief, uninformed guess) vs facts (know, informed observation).

@Bart: What non-experts thinks is irrelevant, the real debate was over decades ago. You can reject facts, but that is irrational.
my2cts
3.7 / 5 (6) Jan 19, 2016
Anonym, it is all part of the worldwide "global-warming" movement, made up of people who like to claim that man can indeed have the power change long-term weather, so that they can slap arbitrary restrictions and regulations in controlling the masses in all areas of life.

Of course it is silly, and many serious people don't believe this stuff is real.

Not as silly as the stuff you are usually pushing here.
Tell us how Life and Truth are The Most Important in Life and Truth !
And how we are all murderers, that is your usual narrative.

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