did climate change start in the neolithic ?

[CrazyDonkey]

Why the snarky responses?

I'm not claiming that it is a slam dunk, just that it isn't utterly implausible. The case laid out (in the links I provided) does fit the timeline of temperature peaks and dips (that you provided). If humans had an effect, I don't think they were the only factors driving these changes - I specifically stated that the post-glacial warm period (~6k-7k BCE) was likely "due to decreased reflection off ice sheets and methane releases from melting permafrost," not farming.

 

[LeBrok]

Why the snarky responses?

Sorry about that.

I'm not claiming that it is a slam dunk, just that it isn't utterly implausible. The case laid out (in the links I provided) does fit the timeline of temperature peaks and dips (that you provided). If humans had an effect, I don't think they were the only factors driving these changes - I specifically stated that the post-glacial warm period (~6k-7k BCE) was likely "due to decreased reflection off ice sheets and methane releases from melting permafrost," not farming.

These are more like enforcing the trend effects, not the causes of warming. You see, something had to warm up the planet in first place to melt the ice, which exposed the ground and released some methane. This something, whatever it is (probably amount of sun radiation reaching earth), is the main cause and way much stronger than anything else. Pretty much overrules the rest.

 

[CrazyDonkey]

The "peaks" and "dips" are a product of the graph's scale, which compresses the data.

I'm not discounting that natural cycles were major driving factors. The retreat of the glaciers meant more solar heat was absorbed rather than reflected into space, while the melting of the permafrost released large amounts of methane, a potent greenhouse gas - those factors likely caused the atmosphere to warm up beyond what would otherwise have been the case (much warmer than it is now). Reforestation, as a result, however, ended up pulling carbon out of the atmosphere, cooling the planet.

It wasn't the farming that pumped massive amounts of carbon into the atmosphere, but the burning:

Large-scale fires in western and southeastern states can pump as much carbon dioxide into the atmosphere in a few weeks as the states' entire motor vehicle traffic in a year, according to newly published research by scientists at the National Center for Atmospheric Research (NCAR) and the University of Colorado at Boulder.

Overall, the study estimates that U.S. fires release about 290 million metric tons of carbon dioxide a year, the equivalent of 4 to 6 percent of the nation's carbon dioxide emissions from fossil fuel burning.

"A striking implication of very large wildfires is that a severe fire season lasting only one or two months can release as much carbon as the annual emissions from the entire transportation or energy sector of an individual state," the paper states.

Fires contribute a higher proportion of carbon dioxide in several western and southeastern states, especially Alaska, Idaho, Oregon, Montana, Washington, Arkansas, Mississippi and Arizona. Particularly large fires can release enormous pulses of carbon dioxide rapidly into the atmosphere.

https://www.nsf.gov/news/news_summ.jsp?cntn_id=110580

Nor should we discount the role of wildfires, whether sparked by lightening or humans. Droughts during warm periods (much warmer than now) could have caused massive forest fires. What role humans had, running around with torches, lighting the undergrowth on fire, isn't clear. According to the study that was linked, for each acre under cultivation, five more lay farmed out and untreed, at any one time.

In many cases, the "cold periods" correspond to human cultural collapses. While the first (due to vulcanism?) likely played a role in causing the second, the shrinking of fields under cultivation would have led to reforestation, pulling carbon out of the atmosphere, cooling the climate even further. Note the cold period that followed the medieval warm period - the population collapse from the Black Plague would have led to large-scale reforestation.