This Nature article is behind a pay wall so I will do my best to summarize it here:
Paleoclimatologist W. Ruddiman bases his theory on carbon dioxide and methane trends. In between ice ages, CO2 rises quickly at first and then declines until the next ice age settles in. But 8000 years ago, coincident with human agriculture, CO2 levels started to rise instead of decline, and apparently the same thing happened with methane 5000 ears ago. His theory is criticized because the human population was too small at that time to have provoked such changes. In support of Rudimann's hypothesis, Swiss scientist Jed Kaplan built a model of land-use over time, based on historical and archaeological data and concluded that humans cleared more land early on, about twice as much as previously thought. Dorian Fuller, a British archaeologist, has been studying methane emissions from livestock and the spread of rice agriculture in southeast Asia and says his studies suggest that the expansion of rice could account for up to 80% of the additional atmospheric methane as of 1,000 years ago.
Both Fuller and Kaplan think the early imprint of humans on climate is there, and is real, and thjat the idea that humans did not influence the climate until the Industrial Revolution should be discarded.
Models bolster case for early human effect on greenhouse-gas levels.
Scientists have come up with new evidence in support of the controversial idea that humanity's influence on climate began not during the industrial revolution, but thousands of years ago. Proposed by palaeoclimatologist William Ruddiman in 2003, the theory says that human influences offset the imminent plunge into another ice age and helped create the relatively stable climate that we are familiar with today. It has been repeatedly panned as implausible by palaeoclimate researchers, but eight years on, Ruddiman and others say that they have the data to support early anthropogenic climate change.
Interesting, I wonder if our presence has been enough to prevent the onslaught of a new ice age or are we in just a long minor ice age right now. I need to go look up paleoclimatic models.
Let's face it - we have been making a mess for tens of thousands of years. Fires in Australia, killing the large mammals in North America and causing deforestation in the Middle East, North Africa and Europe.
With the rise of the agricultural revolution forests were cleared through burning to plant crops, cultivate livestock, and flush prey. It would be interesting to know how many trees were cut down between the 8,000 and 9,000 years ago - through to today for that matter.
Here are some other articles worth reading
Why We Must Phase out Coal Emissions a Core Climate Solution?
Is coal with carbon capture and storage a core climate solution?
From Nature's The Great Beyond:
So did climate cause the evacuation? Or did drought exacerbate other problems? Spaniards entered the region around the same time, so could disease have played a role? If so, wouldn't archaeologists have found evidence? These are just a few of the questions that arose Thursday as two busloads of scientists explored Bandelier National Monument. They saw ruins, petroglyphs and "cavates" - chambers carved into volcanic walls, which added real estate to much larger housing complexes in the local canyons (modern reconstruction and cavates pictured above). Plenty of ideas were offered up, but definitive answers were hard to come by.
It was an appropriate outing for the 100 or so scientists attending the American Geophysical Union's Chapman Conference on Climates, Past Landscapes, and Civilizations this week in Santa Fe. All week scientists representing various disciplines - from geology and paleoclimatology to archaeology and botany - presented their latest data illustrating how climate has affected various civilizations throughout space and time as well as how and when civilization has affected climate. Time and again we saw paleoclimate data lined up against major events in human history. Time and again we were left to ponder whether coincidence translates into causation. Time and again we wondered whether it wouldn't be useful if scientists from different disciplines spent more time talking to each other.
That was of course the point. Peter Clift, a geologist at University of Aberdeen and the principle convener, started thinking about archaeology as a result of work in Pakistan that could shed light on the rise and fall of the Indus Valley civilization. "Instead of geologists and archeologists guessing what each other were doing," he says, "I thought we should have a meeting."
For Harvey Weiss, an archaeologist at Yale University in New Haven, a core message is that the Holocene - the scientific name for the post-glacial world we all know and love - isn't the calm place that it is often assumed to be. "The dynamic quality of the Holocene, for agricultural societies, is extremely challenging - if not overwhelming," says Weiss. "It's very difficult for archaeologists to accept this, but there is a pattern of abandonment."
It's the pattern part that is new, the idea that paleoclimate data can be combined with geology, climatology, oceanography and archaeology to provide context and bring order to human history. It's the pursuit of sweeping explanations, which are almost always appealing - even if they are wrong. And although nobody would question the value of synthesis and interdisciplinary work, it's the "wrong" part that elicited occasional words of caution.
Just looking at the inevitable ups and downs graphed over the past millennium, it might seem like a coin toss as to whether any given event or societal collapse correlates with drought. It also becomes quite clear that societies actually withstood many such droughts, a point made quite forcefully as the conference was winding down Friday afternoon by James Aimers, an assistant professor of anthropology at the State University of New York, Geneseo.
"Climate doesn't explain it all," Aimers warned, accusing climate scientists and archaeologists alike of playing loose with each other's data. "Very simply, the drought explanation flattens complexity."
Archaeologists at Bandelier have found evidence of trading with distant societies, evidence of a network that might have helped spread the risk and sustain communities during hard times. These days globalization represents the ultimate risk-disperser at the human scale, making widespread collapse exceedingly unlikely absent a truly global threat ... such as global warming, of the most catastrophic caliber. And although the conference focused on the past, the future served as an ever-present backdrop.
For Robert Gibson, a non-scientist advisor to the Climate Change Business Forum in Hong Kong, this question was central: Could a better understanding of the blows that climate has dealt people in the past help people make wiser decisions about global warming today? "I think I and the vast majority of the population live in a world where the coastline doesn't change, where the climate is stable," he said, underscoring an entire conference full of evidence to the contrary. "The question is how to get the message out."