Question- Pre-industrial human impact on greenhouse effect & global temperature?

raharris1973

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Did this occur? Could it have occurred?

It's widely accepted that pre-industrial and even pre-agricultural humans affected the environment (hunting megafauna to extinction, exhausting local forest or soil resources), but did human activities prior to the 1700s affect atmospheric carbon dioxide levels and global cooling and warming trends in historic times?

For instance, did the crash of Amerindian populations in the century after contact intensify or cause the severe cooling trends of the 1600s? Mechanism could have been reduction in carbon dioxide producing human population, maybe compounded by reforestation of depopulated lands.

On the other hand, the introduction of new world crops like potatoes and maize enabled major expansion of cultivation and in turn of old world populations from Ireland to China. In terms of global population levels, I wonder if increased populations in the old world simultaneously offset or more than offset the new world population crash.
 
I have read that the Mongolian invasions reduced the population so much that forest where able to reclaim large portions of land. This caused a reduction in CO2 and therefore cooler temperatures. Mind you this is a theory.

Deforestation is the only thing I can think of that pre industry cultures can do. They just weren't emitting enough to off set natural carbon sinks (the oceans).
 
Did this occur? Could it have occurred?

It's widely accepted that pre-industrial and even pre-agricultural humans affected the environment (hunting megafauna to extinction, exhausting local forest or soil resources), but did human activities prior to the 1700s affect atmospheric carbon dioxide levels and global cooling and warming trends in historic times?

For instance, did the crash of Amerindian populations in the century after contact intensify or cause the severe cooling trends of the 1600s? Mechanism could have been reduction in carbon dioxide producing human population, maybe compounded by reforestation of depopulated lands.

On the other hand, the introduction of new world crops like potatoes and maize enabled major expansion of cultivation and in turn of old world populations from Ireland to China. In terms of global population levels, I wonder if increased populations in the old world simultaneously offset or more than offset the new world population crash.

Yes, the crash of Amerind populations severely altered forest patterns in North America and likely exacerbated the climate change of the 1600s
 
For instance, did the crash of Amerindian populations in the century after contact intensify or cause the severe cooling trends of the 1600s? Mechanism could have been reduction in carbon dioxide producing human population, maybe compounded by reforestation of depopulated lands.

This is now generally accepted in academia as highly contributing to the Little Ice Age.

Example papers: Here, here, here.
 
There was a Scientific American article some years ago that looked at this question. Their conclusion was that the introduction of agriculture, especially rice farming, had a substantial effect on global temperatures. Both rice paddies and cattle produce large quantities of methane, a very potent greenhouse gas, while clearing land for agriculture results in substantial extra CO2 in the atmosphere as well. I distinctly remember a graphic in the article, that showed a strong correlation between global temperatures and the extent of cleared land for agriculture, the extent of rice paddies, and the estimated worldwide number of domestic cattle.

Their conclusion was that in the absence of agriculture (and modern industry), we would currently be sliding into the next ice age by now. At this amount of time from the start of previous interglacials, global temperatures were almost always going into an increasingly rapid decline.
 
This is now generally accepted in academia as highly contributing to the Little Ice Age.

Example papers: Here, here, here.

The start of the Little Ice Age is in dispute, but cooling seems to have started as early as the mid-13th century (with expansion of pack ice) and probably accounts for the European famines of 1315-1317 and cooler temperatures throughout the 14th and 15th century which is clearly before Columbus.

So even if a population crash in the 1600s impacted cooling, the Little Ice Age was already happening and its origins had nothing to do with the collapse in the American Indian population. It may have been a contributor to the later stages of the Little Ice Age, but overall it seems there are much deeper forces at work completely independent of Man.
 

Dorozhand

Banned
There was a Scientific American article some years ago that looked at this question. Their conclusion was that the introduction of agriculture, especially rice farming, had a substantial effect on global temperatures. Both rice paddies and cattle produce large quantities of methane, a very potent greenhouse gas, while clearing land for agriculture results in substantial extra CO2 in the atmosphere as well. I distinctly remember a graphic in the article, that showed a strong correlation between global temperatures and the extent of cleared land for agriculture, the extent of rice paddies, and the estimated worldwide number of domestic cattle.

Their conclusion was that in the absence of agriculture (and modern industry), we would currently be sliding into the next ice age by now. At this amount of time from the start of previous interglacials, global temperatures were almost always going into an increasingly rapid decline.

That's really interesting. If world temperatures have been in a downward spiral since the start of these periods, I wonder if the earth may ultimately become a snowball again in the absence of continued human activity.
 
With all the fuss over fossil fuels, people tend to forget how much CO2 slash-and-burn agriculture dumps back into the atmosphere. Granted, that carbon dioxide is already free (that is not locked for hundreds of millions of years underground), but it did have its impact.
 

Dorozhand

Banned
With all the fuss over fossil fuels, people tend to forget how much CO2 slash-and-burn agriculture dumps back into the atmosphere. Granted, that carbon dioxide is already free (that is not locked for hundreds of millions of years underground), but it did have its impact.

Absolutely. We need to start thinking of sustainable alternatives to traditional agriculture along with traditional manufacturing.

Vertical gardens are the future man! :cool:
 
With all the fuss over fossil fuels, people tend to forget how much CO2 slash-and-burn agriculture dumps back into the atmosphere. Granted, that carbon dioxide is already free (that is not locked for hundreds of millions of years underground), but it did have its impact.
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A common hunting method was to set fire to grasslands to drive hunted animals to a wanted location. According to '1491' before iron tools widespread burning was used for forest management in many cultures. In all cases the fires burned themselves out or were put out by rain. In many farming areas around the world fields were burned after harvest to kill weeds and fertilize the land. And don't forget all the massive methane farting animal herds in Africa, India, and the Americas.
 
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The start of the Little Ice Age is in dispute, but cooling seems to have started as early as the mid-13th century (with expansion of pack ice) and probably accounts for the European famines of 1315-1317 and cooler temperatures throughout the 14th and 15th century which is clearly before Columbus.

So even if a population crash in the 1600s impacted cooling, the Little Ice Age was already happening and its origins had nothing to do with the collapse in the American Indian population. It may have been a contributor to the later stages of the Little Ice Age, but overall it seems there are much deeper forces at work completely independent of Man.

Its very possible that the medieval warming period caused melting of the ice sheets. The fresh water then slowed down global ocean currents. This would have be the first domino. The human dependent causes would have been part of a negative feedback loop. Which is scary because we are past the temps of the medieval warming period.
 
That's really interesting. If world temperatures have been in a downward spiral since the start of these periods, I wonder if the earth may ultimately become a snowball again in the absence of continued human activity.
Unlikely; the Little Ice Age seems to have ended more or less on its own before CO2 levels really started to rise precipitously.
 
If you want really, really pre-industrial human impact, there's a common belief that the forests of Bronze Age Britain (and Europe and other similar climes, by extension) were basically wiped out with the development of metal axes, probably due to slash-and-burn farming. So doubtlessly that would have increased carbon output into the atmosphere.

Although there's also a more recent theory that states that the coverage of pre-historic forests in Britain has been grossly exaggerated, and was in reality patchy at best and constantly cycling between forested land and semi-barren grassland. So humans might not have had as large an impact as was previously thought after all.
 
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