Conversation

Theories of rare and extreme events are really inadequate. Neither extreme statistical bounding (9-sigma, 12-sigma…), nor catch-all categories like “black swan” or “long-tail events” really get you anywhere helpful.
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The most salient feature of rare+extreme is ontological explosions. In going from 1 to 3 sigmas of phenomenological coverage, parametric range only increases about 50% but variety can explode orders of magnitude.
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1-sigma of household pets is 2 species (cats and dogs). 3-sigma is maybe 10? You can include goldfish, parrots, hamsters. But at 6-sigma, you get insane numbers, like Pablo’s hippos, people in Texas with tigers… any exotic species that can plausibly be a pet for some nutjob
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This is relevant to extreme weather. “A year’s rain in a day” is “extreme rain” the way a hippo is a horse. It’s an ontologically distinct type of weather event. The jet stream destabilizing isn’t just seasonal weather, it’s like an Australia-worth of “weather event” species.
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I’d like an extreme weather index that tracks variety. The historical frequency fails to convey information past a point. “Aliens have landed” is an event that fast happened in all 6000-odd years of recorded human history as far as we know. That’s… not a useful observation.
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