[redgolum]

My father has an old tape of a talk by a Dr. Browning that said much the same thing. Many civilizations rise and fall do to climate. What is interesting is what he said in the next section. Those climate changes don't have alot to do with anything man does. One good volcano (not a big one, but an "average size" one) puts up more particulate matter into the air quicker than we could if we ground up all of our trash and dumped it into the stratosphere.

I also saw this when I was working in New Mexico. At the time of the Spanish settlement of the area, it was a pretty good place to grow corn and other crops. Good rain fall, mild winters, etc. Guess what, a lot of the local tribes had moved into that area because their home ground was in a severe decades long drought. In short, the Southwest was a good place to grow crops (in the 1600's) and the upper Midwest was dang near a desert. And then the climate changed. All this was well before there were enough people to have much of an effect (Europe was recovering from the Plague).

[cogitator]

One good volcano (not a big one, but an "average size" one) puts up more particulate matter into the air quicker than we could if we ground up all of our trash and dumped it into the stratosphere.

Yes, but ash doesn't stay aloft long. SO2 stays aloft a bit longer. The climate effects of one major volcanic eruption won't last more than 3-4 years. (This does not address supervolcanoes.)