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View Full Version : Global Warming? Blame cavemen.


Potemkin
08-17-2009, 08:29 PM
http://www.sciencedaily.com/releases/2009/08/090817073502.htm

Agricultural Methods Of Early Civilizations May Have Altered Global Climate

ScienceDaily (Aug. 17, 2009) Massive burning of forests for agriculture thousands of years ago may have increased atmospheric carbon dioxide enough to alter global climate and usher in a warming trend that continues today, according to a new study that appears online Aug. 17 in the journal Quaternary Science Reviews.

Researchers at the University of Virginia and the University of Maryland-Baltimore County say that today's 6 billion people use about 90 percent less land per person for growing food than was used by far smaller populations early in the development of civilization. Those early societies likely relied on slash-and-burn techniques to clear large tracts of land for relatively small levels of food production.

"They used more land for farming because they had little incentive to maximize yield from less land, and because there was plenty of forest to burn," said William Ruddiman, the lead author and a professor emeritus of environmental sciences at the University of Virginia. "They may have inadvertently altered the climate."

Ruddiman is a climate scientist who specializes in investigating ocean-sediment and ice-core records. In recent years he has searched across scientific disciplines anthropology, archaeology, population dynamics, climatology to gain insight into how humans may have affected climate over the millennia.

He said that early populations likely used a land-clearing method that involved burning forests, then planting crop seed among the dead stumps in the enriched soil. They would use a large plot until the yield began to decline, and then would burn off another area of forest for planting.

They would continue this form of rotation farming, ever expanding the cleared areas as their populations grew. They possibly cleared five or more times more land than they actually farmed at any given time. It was only as populations grew much larger, and less land was available for farming or for laying fallow, that societies adopted more intensive farming techniques and slowly gained more food yield from less land.

Ruddiman notes that with the highly efficient and intensive farming of today, growing populations are using less land per capita for agriculture. Forests are returning in many parts of the world, including the northeastern United States, Europe, Canada, Russia and even parts of China.

The positive environmental effects of this reforestation, however, are being canceled out by the large-scale burning of fossil fuels since the advent of the Industrial Revolution, which began about 150 years ago. Humans continue to add excessive levels of carbon dioxide to the atmosphere, contributing to a global warming trend, Ruddiman said.

Five years ago, Ruddiman made headlines with a hypothesis that humans began altering global climate thousands of years ago, not just since the Industrial Revolution. That theory has since been criticized by some climate scientists who believe that early populations were too small to create enough carbon dioxide to alter climate.

According to projections from some models of past land use, large-scale land clearing and resulting carbon emissions have only occurred during the industrial era, as a result of huge increases in population.

But Ruddiman, and his co-author Erle Ellis, an ecologist at UMBC who specializes in land-use change, say these models are not accounting for the possibly large effects on climate likely caused by early farming methods.

"Many climate models assume that land use in the past was similar to land use today; and that the great population explosion of the past 150 years has increased land use proportionally," Ellis said. "We are proposing that much smaller earlier populations used much more land per person, and may have more greatly affected climate than current models reflect."

Ruddiman and Ellis based their finding on several studies by anthropologists, archaeologists and paleoecologists indicating that early civilizations used a great amount of land to grow relatively small amounts of food. The researchers compared what they found with the way most land-use models are designed, and found a disconnect between modeling and field-based studies.

"It was only as our populations grew larger over thousands of years, and needed more food, that we improved farming technologies enough to begin using less land for more yield," Ruddiman said. "We suggest in this paper that climate modelers might consider how land use has changed over time, and how this may have affected the climate."

Kassy
08-19-2009, 05:50 AM
ScienceDaily (Aug. 17, 2009) — Massive burning of forests for agriculture thousands of years ago may have increased atmospheric carbon dioxide enough to alter global climate and usher in a warming trend that continues today, according to a new study that appears online Aug. 17 in the journal Quaternary Science Reviews.

Cavemen were mostly hunters and gatherers.


The last glacial period was the most recent glacial period within the current ice age, occurring in the Pleistocene epoch. It began about 110,000 years ago and ended about 9,600 - 9,700 BC. During this period there were several changes between glacier advance and retreat. The maximum extent of glaciation was approximately 18,000 years ago.

http://en.wikipedia.org/wiki/Last_glacial_period

Total world population was somewhere between 5 and 10 million at the time people started farming (around 7000 BCE) which was only after the last ice age.

Probably they didn't have to use too much slash in burn in the agricultural centers of those days (think the Nile, Yangtze & Fertile Crescent).

They might have used a lot more land per person in some areas but i don't think they kept the parts they didn't use free of trees & shrubs. Whatever grows on that land immediately takes up carbon too so it only accelerates the Carbon cycle.

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Much later in history you possibly can see a link between the Black Death, change in landuse (dead people don't need food or firewood) and temperature.

The Black Death is estimated to have killed 30% to 60% of Europe's population, reducing the world's population from an estimated 450 million to between 350 and 375 million in 1400.

Note that is a change of -75 to -100 million , a number more then 10 times bigger then those first farmers.

*

So the numbers don't add up (not enough people, not enough change in land use).

Potemkin
08-19-2009, 09:01 AM
Cavemen were mostly hunters and gatherers.


Don't be so stiff. I was taking literary license with the title.

There is an ad campaign running in the US.

"So easy a caveman can do it."


So the numbers don't add up (not enough people, not enough change in land use).

I am sure the scientist researchers at the two Universities would be glad to see the results of the studies you have performed on this topic.

Oric
08-19-2009, 10:09 AM
Not the cavemen but a famous Turkish historian "Evliya Celebi" states in the 15th century that the Anatolian peninsula (Asian part of modern Turkey) is covered thich with forests so that a squirrel may never come down from a tree travelling from east end to the Aegean Sea. Today the forests only make up 14% of the land. What has been described in the article happened in less than 500 years ..

Sarrah
08-19-2009, 01:16 PM
Here, there are many many fires started each year by lightening. We actually have a lightening season sort of. We have lightening then next day we get a report on how many fires started. So in a season say 500 lightening fires start. That is just this area. We gave the world to have fires start this way.
Ye Olde caveman types couldn't phone the forest service to report a fire. They weren't too up to fire fighting I just betcha.
Also, it is recorded somewhere. Ummm Spanish explorers? British? I read it somewhere a long time ago. Whoever, would cruise along a coast and not being able to see the lay of the land for the forests that grew down to the water. They would set fires to burn it clear so they could get a look.
There have been people and nature setting fires since the earth was created. At least that is the way it seems to me.

Sysiphus
08-19-2009, 01:24 PM
This is a silly theory. The population density and overall population were not anywhere near the level necessary to have any impact on climate at that point. Also, many of the agricultural methods used, such as terra preta, would have sequestered carbon.

Kassy
08-19-2009, 09:52 PM
Don't be so stiff. I was taking literary license with the title.

There is an ad campaign running in the US.

"So easy a caveman can do it."

Sorry ~ i don't watch US adds.

The head line isn't so much of a problem (have seen greater literary ventures though)...stupid article also states:
and usher in a warming trend that continues today

Which either means they found a new trend or they're dead wrong.

Enough meta discussion... the details:
I am sure the scientist researchers at the two Universities would be glad to see the results of the studies you have performed on this topic.


Shouldn't be hard to come by since most come from popular science write ups on the real stuff. It's the sort of stuff you should read before making grandiose claims.

Do you have a point in all this? Why post this in 'science' instead of environment? Etc.

Meanwhile i wish i was as eloquent as ndriley97... :beer:

spimifslop
09-17-2009, 11:29 PM
Good post. I appreciate it
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