Did humans cause the end of the ice age 8,000 years ago?

[Silverhair]

In this months issue of Scientific American, (March 2005 page 46)there is an article that claims that humans, by the agricultural revolution, caused a marked increase in the amount of methane in the air, thereby cause the end of the ice age.

According to the article, the orbital mechanics that cause the ice ages was further chilling the northern hemisphere, and the normal progression of the ice age called for it to be getting colder. Indeed, we should be in a deeper ice age now, than it was then.

While not stated in the article, I find it interesting that the "little ice age" from about 1500 to about 1850 corresponds roughly to the loss of about 1/4 of humanity in the great plague until the industrial revolution was in full swing.

So, what do you think? Have we been warming up the globe for 8,000 years?

[orpupilofnature57]

1. No, but the dominion theocracy will cause the next. eom

[H2O Man]

2. The last one

in NA was the Wisconsin, which receeded 12,000 years ago. Hence it would seem the process had begun before the agricultural revolution was in significant swing. Perhaps the end of the ice age produced an increase in agriculture.

[Silverhair]

4. The article states that is the traditional view.

Take a look at the article. Scientific American is not a magazine that publishes junk science.

[H2O Man]

20. Nor did I say it did.

I think that there should always be new theories, and like when they challenge the previously held assumptions. And, of course, you are correct that I should read the article. But there is pretty solid evidence in North America that shows when human beings moved into the northeast on a more permanent basis, and when certain large game left the scene. I will look forward to reading the article.

[StClone]

3. No to maybe, because

The number of humans at the peak of the mini-Ice Age was many times that the population at the time the last real Ice Age ended. Man seems not to be a significant factor with that knowledge.

It is more likely man evolved when the Earth warmed rather than cause the warming. Also, if the trend of substantial warming can only be dated to the last century it should have been evident much sooner under the theory.

[Silverhair]

6. Humans were already around 70,000 years ago at a minimum.

In fact, recently studies on the DNA of body lice suggests that we started the habit of wearing clothes about that time. At any rate, 70K years ago is even before the onset of the last ice age. So we had already evolved before it started, rather than after.

[Xithras]

10. H. Sapiens has been dated to 100,000 years

The oldest Homo Sapien remains indicate an emergence in modern-day South Africa about 100,000 years ago, and that we spread throughout Eurasia within a few thousand years of that.

Your point still stands though.

[Media_Lies_Daily]

17. I guess you missed this article in the BBC....

....that indicates that you're about 100,000 years off the mark.

Age of ancient humans reassessed
<http://news.bbc.co.uk/2/hi/science/nature/4269299.stm>

Quote:

"Two skulls originally found in 1967 have been shown to be about 195,000 years old, making them the oldest modern human remains known to science.

The age estimate comes from a re-dating of Ethiopian rock layers close to those that yielded the remarkable fossils."

....SNIP....

"The latest dating work is reported in the science journal Nature.

It puts the specimens close to the time expected for the evolutionary emergence of our species. Genetic studies have indicated Homo sapiens arose in East Africa - possibly Ethiopia or Tanzania - just over 200,000 years ago."

[GumboYaYa]

19. I thought that h. sapiens has been dated much farther back than

100,000 years. Someone else cited the recent discovery of remains that appear to be almost 200,000 years. That is the earliest emergence of h. sapiens recorded to date.

I also understood that about 75,000 years ago a supervolcano eruption reduced the number of h. sapiens to the thousands and virtually anhilated life on Earth, killing up to 90% of all living things. Scientists attribute the evolution of human intelligence in its modern form to the fact that only the most intelligent humans survived this period of Earth's history. Genetic tests show that all humans on Earth today are descended from those few thousands of people.

[Xithras]

24. Evolutionary trivia: When is Homo Sapiens not Homo Sapiens?

When he is Homo Sapiens Sapiens.

The problem with dating the emergence of Homo Sapiens is that it was a gradual process, and pinning a specific date down is tough...after all, what makes a "human"?

According to my understanding (which admittedly may be a couple of years out of date), Homo Heidelbergensis begat archaic Homo Sapiens between 300,000 and 400,000 years ago. Archaic Homo Sapiens displaced most of the previously existing Homo populations and pretty much took over the world. Homo Sapiens also never stopped evolving, and about 130,000-150,000 years ago the Homo Sapiens population in South Africa began showing additional evolutionary changes that made them more human. By 100,000 years ago they were a distinct subspecies, Homo Sapiens Sapiens. This subspecies then spread out of Africa and displaced archaic Homo Sapiens by war, interbreeding, or a combination of the two.

Still, the archaic Homo Sapiens would qualify as "human" to most of us here. They did math, they wore clothing, they lived in tribes and hunted together, they probably had spoken language, we know they had mastered the concepts of art and astronomy, and they even had religion and the concept of an afterlife. They looked very similar to us, and since we are a subspecies of theirs, we were probably able to interbreed without any major problems.

So when you're discussing pre-100k year human findings I have to ask, are you talking about our almost-but-not-quite-human archaic Homo Sapiens ancestors, or our modern Homo Sapiens Sapiens ancestors?

[GumboYaYa]

25. Good questions and information.

This is a fascinating topic to me.

From what I understand there are two schools of thought on this. One says that Homo Sapiens evolved in Africa some 200,000-100,000 years ago as a distinct twig on the tree of human evolution and then scattered to populate the Earth, forcing out less evovled humanoid species. The other school asserts that homo sapiens evolved simultaneous across geographic locations from existing humanoid species. I don't know enough about the recent discovery to have an educated opinion, but at first blush it appears to support the former theory and not the latter.

H. Sapiens is distinct from other species because of the size of its brain, but as you point out there were a number of species of humanoids with ever increasing brain size that got us from homo erectus to homo sapiens. As you suggest, it really is a continuum and not specific points.

[Crunchy Frog]

30. According to everything that I've seen,

the genetic evidence only supports the first school of though on that. Modern humans have just about the least genetic diversity of any animal species on Earth. This strongly suggests that all modern humans are descended from a single, small population that existed only relatively recently.

From everthing that I've seen, the second school of thought has been all but rejected by the scientific community.

The Neanderthals actually had slightly larger brains than modern humans, but had physical characteristics that were very distinct from Homo Sapiens. They have also apparently recovered some genetic material and found that to be distinctly different from that of modern humans. The differences in hominid populations were not just in brain size, but in a whole array of physical and genetic characteristics.

[StClone]

22. Elaborating my point further

But we probably evolved in a warmer period. Neanderthals were highly cold adapted but are not H. sapiens. My point was modern man and "modern" activities (animal domestication, agriculture, extensive fire use for more than heat and cooking i.e. land clearing) were what I was indicating, not just H. sapiens evolution.

[Xithras]

5. Absolutely not

First off, the last ice age began waning in some areas as early as 13,000 years ago. Even though some recent archaeological discoveries are now putting the establishment of early agricultural societies as far back as 10K years ago, the ice had already begun receding by that time.

Besides, archeology also shows that agriculture was slow to spread out of the Indus Valley and Middle East, and that it likely took several thousand additional years for agriculture to spread globally. There were no books, no TV's, no Internet, and no radio back then, and farming practices only spread when a hunter from one village visited a farming village and took the knowledge back home with him. The slow rate at which agricultural technology spread pushed the global emergence of agrarian societies well past the date at which the ice ages ended.

Finally, major methane releases from agriculture are usually the result of tilling the ground. The plow wasn't invented until about 6,000 years ago, and the heavy plow capable of overturning large amounts of soil is only about 2000 years old. Prior to that, agriculture was limited to digging holes and planting seeds one at a time, a process little different than what plants do naturally.

I'd still be interested in reading the article, but I let my SciAm subscription lapse last year.

[Silverhair]

8. Irrigated rice farming produces huge amounts of methane.

He believes that the discovery of rice farming in China was the cause of all the methane.

[Xithras]

14. That is extremely unlikely.

The entire human population living in the area we now call China probably wouldn't have been more than a couple hundred thousand people 10K years ago, and a population that small simply couldn't have established an agricultural society large enough to affect the global climate. Any methane emissions they made wouldn't have even been a blip on a global scale.

Even that makes some serious leaps in credulity. DNA evidence does indicate that rice domestication began in Asia about 10K years ago, but there's no reliable evidence to indicate that they began large scale irrigated rice farming before 5500BC. Rice farming carried out before that probably occurred along riverbanks and lakeshores, where water was natually present and the ground was naturally fertile. That lack of irrigated rice farming prevented its widespread adoption as a food staple for several thousand years.

Again, we end up well past the end of the last ice age.

[DrGonzoLives]

27. Exactly

The population of humans on the planet would have been much smaller - this little thing called medicine hadn't really been studied yet, and the hardships of life would've brought down the desire to screw and make more baby humans.

It's an interesting hypothesis, one worthy of discussion, I just don't see it turning out to be true.

[Jacobin]

7. The globe has been warming and cooling for billions of years

It is now warming.

Whether it is due to normal fluctuations or the climate or temp is increasing as a result of man no one knows. Why not limit fossil fuels and look seriously at alternative fuel sources rather than guess who is right and who is wrong?

[Silverhair]

9. I have posted numerous times about ThermoDepolymerization.

If it works, it will solve the peak oil problem, and several others besides.

However, I enjoy some discussions simply for their own sake. This is one of them.

[Johonny]

15. As Science

pointed out again in December there is consensus that anthropomorphic driven climate change is a reality. Basically we DO know and the thought that there is open debate in the scientific community is not true.

[Xithras]

21. Not exactly

There IS concensus that anthropomorphic climate change is real, but there is still a great deal of debate whether we're causing all of it (unlikely) or whether we're exacerbating the effects of a natually occurring warming cycle (very likely). There is also some debate as to the role that increasing solar output plays in global warming (solar output is at its highest recorded levels in 60 years). Finally, there's the unresolved debate regarding the role of deforestation in global warming (largely undiscussed in the mass media). Forests are vast CO2 sinks, and the last few centuries have witnessed large scale deforestation in Europe, North America, South America, and Asia. More than half of the worlds forests have been removed over the past couple hundred years, a loss which directly correlates to the increase in global CO2 levels and global warming.

[Johonny]

26. Well exactly

"There IS consensus that anthropomorphic climate change is real"

Pretty much all I said. The rest of what you said is correct but my only point was it's a real effect. People use the current debate to dismiss global warming but the scientific discussion has moved to how big an effect is likely, if there is a ceiling and what factors contribute to sources and sinks.

Clearly looking a paleoclimate change non-anthropomorphic change is not only possible but can have effects much greater than that we see today.

[HereSince1628]

11. What about wax and wain of other ice ages?

The geologic record includes evidence of glaciation episodes separated by vast periods of time. Many of them before agriculture could be considered. Are we to believe that Dino-farts influenced truly ancient episodes of glaciation?

Reasonable defense of humans as the cause of the Wisconsin/Wurm episode requires discounting other explanations used to account for the terminations of other glacial epochs.

[Silverhair]

12. According to the article, this one terminated early.

The others matched the orbital cycle.

[Johonny]

13. As far

as I remember the Ice age cycle does not exactly follow orbital mechanics cycle and that the ice ages cycle. It's not a simple system that can easily be modeled with just orbital mechanics. I would agree that the warming of the earth lead to more human farming rather than the reverse.

[Xithras]

18. And there's the biggest problem with his theory.

The author is assuming that precession is the sole cause of the Ice Ages, a stance that no reputable scientist would ever support. Yes, there does appear to be some correlation between ice ages and precessionary intervals, but it's not a 1/1 relationship. Many intervals apparently passed without any ice ages at all, and other ice ages were so long that they spanned several intervals.

While nobody knows exactly what triggers ice ages, they are most likely the result of a complicated dynamic interaction between solar output (solar output varies considerably over millenia), precession (the gradual rotation of the poles through the sky), the distance of the Earth from the sun, position and height of the continents, ocean circulation patterns (affected by freshwater runoff and atmospheric temperature), the composition of the atmosphere, and quite possibly even galactic dust interacting with our solar systems heliopause.

The best theory at the moment is that ice ages are caused by precession PLUS one or more of these other factors working together. If one of these other factors changed, the ice age could have come to an abrupt end without any human interference. In all likelyhood, that's exactly what happened.

[Hugin]

16. At that time there were only a few million people around...

So, I doubt agriculture had a large impact.

I have a cool chart in one of my old atlases
showing population growth.

The warming had more to do with changes in the
ocean currents.

The little ice age a hundred or so years ago
happened when there were way more people and
agriculture.

[amazona]

23. thought it was the other way round

I thought the general idea was that the interglacial allowed humans to get into agriculture. There were regular glacial/interglacials every 10,000 years for awhile you know.

I don't believe the human agricultural revolution of that time would be sufficient to make up for the methane lost from all the farts of all the large mega-fauna lost throughout the world in that time frame. You may laugh, but it has been determined that methane placed in the atmosphere can have a significant impact on climate. We worry now about the huge cattle herds...but keep in mind that 10,000 years ago there were huge herds of such things as mammoths, wooly rhinos, and other large animals throughout the world. The spread of humanity at the end of the interglacial, and the spread of new diseases with them, killed all of these animals down even to the level of killing every horse in the Americas!! (The wild horses in the Americas today were introduced by the Spanish invaders.) There were woolly rhinoceros in Louisiana, these were not rare beasts. So, no, I don't believe people raising wheat, rice, and turnips could possibly make up for all that lost methane production.


But maybe I will change my mind after having read the article, who knows.

The conservation movement is a breeding ground of communists
and other subversives. We intend to clean them out,
even if it means rounding up every birdwatcher in the country.
--John Mitchell, US Attorney General 1969-72

[Silverhair]

28. Thank you all for an excellent discussion and for your contributions. NT

[Crunchy Frog]

29. That doesn't sound very persuasive to me

according to my understanding of the timelines in question. The last ice age actually ended around 1200 years ago, not 8000. According to everything that I've ever read, the agricultural revolution was itself precipitated by the climate change that ended the ice age, ie, the change in climate allowed agriculture to emerge, which had not really been feasible prior to that period.

At any rate, agriculture began among a very small group of people in a very small region of the world, and only spread outward very gradually over thousands of years. The population of humans at the time was miniscule compared to what it is today. I simply cannot imagine how a tiny population of humans in the fertile crescent, deliberately cultivating certain food plants could have possibly been enough to trigger that level of climate change.

I suppose it is possible that by several thousand years later, human population size, and agricultural activities could have become large scale enough to have an impact on climate, maybe to the extent of preventing the emergence of a new ice age. Maybe that's what the article is suggesting. I haven't read it yet, so I don't really know what it is that they're actually trying to say.

[On the Road]

31. More Powerful Than Agriculture

may have been deforestation. Don't know when that happenned in relation to the end of the ice age, but large parts of the Mediterranean and Near East were stripped of their forests by ancient civilizations.

[Zorro]

Stark evidence of the effects of deforestation can be seen at Troy

The ancient site is several miles away from the Med, when in historical times it was supposedly a seaport. The theory is that the accumulation of soil between the site and the coast is the result of deforestation in North Africa, with the winds blowing loose soil eastward to the coast of Asia Minor.

From a timeline perspective it roughly correlates to the change to the environment in North Africa, from a relatively wet climate to desert.

Crete is another example of the effects of deforestation, but in this case it was a combination of humans and livestock (particularly goats) that denuded a lot of the terrain over the millennia.

[DU GrovelBot]

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[FogerRox]

33. There many "Cycles" at play here. The S A articles seems narrow

minded to me.

500 yr old Wheat fields in Greenland-Earth was warmer?
800 yr old villages-now underwater off the coast of NJ.
Earth was colder?

Mars and Earth get close every 60k years.

These are recent events.

This guy in S.A. gets down with info that doesn't check out on a geological scale--he talks about the near past with seemingly no cognizance of what happened 100k or 500k years ago.