Was it those nasty 1st century Romans who caused the global warming of the late middle ages? Were they emitting too much methane at their orgies? Did the Elizabethans not burn enough wood to counteract the little ice age of the 19th century? ;~))
Even with an industrial society world-wide, man-made greenhouse gases are inconsequential. Natural sources absolutly dwarf anything that man could hope to produce. Nature will do what it wants on a global scale and we are virtually powerless to control it one way or another. One minor burp of the sun, which burps very regularly when measured against the eons, can either fry us or freeze us within minutes. We have no control over the global environment. We can act on local problems but globally, we are powerless. It's arrogance to think that nature cares one way or another what we do or if we even exist. We are virtually a nothing on a global scale. Nature adjusts in ways we have little or no comprehension of.
Must be --- and the Vostok data seem to show that every 100,000 years there has been manmade warming ---