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What’s in a standard deviation?

Temperature reconstructions for the Holocene period from 11,300 years BP to 2012.
Marcott et al. in purple (with blue confidence interval) Mann et al. in grey (from paper)

We all remember the standard deviation bell curve from high school statistics; the more you vary from the mean, the less likely it is that will happen again because around 68% of the population will fit into the first standard deviation either side of the mean.

However, the important bit you need to keep in mind when reading about this paper is that standard deviation curves have three standard deviations on either side of the mean, which covers 99.7% of all the data. The odds that a data point will be outside three standard deviations from the mean is 0.1% either side.

What does high school statistics have to do with global temperature reconstructions? Well, it’s always good to see what’s happening in the world within context. Unless we can see comparisons to what has come before, it can be really hard to see what is and isn’t weird when we’re living in the middle of it.

The famous ‘Hockey Stick’ graph that was constructed for the past 1,500 years by eminent climate scientist Michael Mann showed us how weird the current warming trend is compared to recent geologic history. But how does that compare to all of the Holocene period?

Well, we live in unusual times. 

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