Hoisted from Comments: Robert Waldmann on Positive Climate Feedback Loops, Snowball Earth, and Evolution
More Bad Climate Science from the Wall Street Journal Editorial Page...: One doesn't have to go all the way back to snowball earth to know that the Lindzen is full of it. Ice ages come and go with, evidently, very subtle forcing due to the Earth's wobble. I don't see how anyone can doubt that there is strong positive feedback around the current temperature.
Now snowball earth is fascinating for the reason that Hoffman and Schrag just started when you stopped the tape. According to H and S, the Earth was a snowball just before the Cambrian explosion -- All sorts of fossiles suddenly appear. Now one hint of an explanation is in the "grinding glaciers" and then "extreme erosion" parts of their story. Since I heard of the snowball earth hypothesis I wonder if the cambrian explosion is so explosive partly because late pre-cambrian fossils were destroyed by glaciers and erosion and such -- crushing, grinding, dissolving eroding all sound like destroying the then relatively recent fossil record.
Also maybe the explosion had something to do with the near extinction of life. Geographic isolation of small groups of organisms causes an increase in diversity. It is suspected (by Sewell shifting balance Wright et al) that such isolation is required for major evolutionary change which almost has to pass through not very fit halfway to the new life form stages and so might require random drift down a fitness gradient.
If life was restricted to isolated patches around volcanos one could imagine that the life in each hot spot would end up very different. Then when the ice melts you have great diversity (for a while).
Finally constrained areas can promote gigantism. When organisms can spread it helps to reproduce quickly. When they are stuck with each other, fighting over meager food, it helps to be a bit bigger than the other guy. It is sometimes suspected that there was a whole lot of variety in the pre-cambrian but the animals were just not big enough to leave fossils.
So the part they were about to get to when you cut their mikes is great too.