You reference the snowball earth, and I'd like to point out (or emphasize) the opposite applies as well. Many times in the past (as I understand it) CO2 levels

You reference the snowball earth, and I'd like to point out (or emphasize) the opposite applies as well. Many times in the past (as I understand it) CO2 levels have been dramatically higher than they are today. If a runaway greenhouse effect was likely triggered by these tiny increases in CO2 (as proportion of atmosphere) claimed by proponents of AGW, wouldn't it have been triggered in the past, when CO2 levels were vastly higher? Two opposite situations that one could plausibly argue would result in a runaway effect to an extreme equilibrium where humans couldn't survive. They both sound plausible, but despite having experienced both ice ages and dramatically higher CO2 (and temperatures) in the past, the predictions have not happened.