In late September, I wrote a note on whether
Lake Superior still remembers the last ice age. The answer was no (read that post for why). But along the way I illustrated a simple sanity check that would have given the author I was responding to a heads up that he was seriously wrong.
The check I used was to compare volumes. If something the volume of Lake Superior remembered conditions for 10,000 years, then something with 100,000 times the volume would (could/should/...) take 100,000 times as long to adjust. The ocean is that much bigger, so would take that much longer. Yet we know (sanity) that the ocean's circulation time is only a few hundred to a few thousand years.
This doesn't prove that the original 10,000 year estimate was wrong. That's not the purpose of a sanity check. Rather, the sanity check alerts us to examine the system more carefully. Maybe there's something fundamentally wrong about using volume for comparison, maybe there's something fundamentally wrong about what lead that author to saying 10,000 year memory for Lake Superior. As we found out, it is the original claim of 10,000 years that was severely wrong. (Turned out to be about 6 months.)
In the comments, though, there were some noting that my approach to sanity check wasn't right. Or at least that I could have made a better estimate than I did. Since I take sanity checking to be a heads up process rather than a proof, I'm not very concerned with whether I chose the most accurate (I did choose one of the simplest) method. But it is worth its own discussion how you might make better estimates.
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