How to compare disasters and risk

This post is basically a concise, compact version of an article I just read in The Wall Street Journal titled, “Putting Fukushima into perspective,” by David Roberts. He is “a former academic physicist” and “was the science adviser to the US ambassador to Japan from 2011-12,” so I think he’s maybe a little bit credible.

It is important for us to be able to understand how comparable two events are, taking Roberts’ example of the nuclear meltdown in Fukushima, it would be helpful to see what the situation is like now, compared to how things were pre-meltdown. Most scientists probably won’t have problems understanding the terms sieverts or becquerels, but for the average person, this isn’t exactly useful. The New York Times accurately described one millisievert as the same as the outermost contamination zone around the 1986 Chernobyl nuclear disaster, making it sound much much worse than it is. I’d hate to read the Daily Mails interpretation of it, they’d still find a way to complain about immigrants.


However, thanks to Stanford’s Professor Ronald Howard and Cambridge’s David Spiegelhalter, we now how the units ‘micromort’ and ‘microlife,’ respectively.

An activity, such as hand-gliding, can now be assigned a number that shows how risky it is, meaning it can be compared to other things like going under general anesthesia. Something assigned one micromort would mean there is a one in a million chance of dying. So for every hand-gliding jump you do, there is an eight in a million chance of dying as that activity is assigned 8 micromorts; going under general anesthesia is given 10 micromorts and giving birth is 120 micromorts. It should be noted at this point that the average person experiences one micromort per day, so this helps put things in perspective.

The micromorts counterpart, the microlife, “represents a 30 minute period in ones expected lifespan.” This unit is great for determining long-term effects, as we know a young adult has around a million microlives to use (48 per day), so from here we can calculate how our lifestyle choices affect us. Smoking 20 cigarettes per day takes 10 microlives per day, whereas exercising for 20 minutes daily adds two microlives per day; no, this does not mean if you exercise a lot you will live forever.

These can now be easily compared to the one millisievert we mentioned before; one millisievert equates roughly to 18 microlives. Living in Fukushima right now would mean you lose one extra microlife every 5 days.

Roberts does note, however, that he, “may be overestimating the risk of living in Fukushima city, for example, due to complexities such as extrapolation and radioactive decay.”

So start applying these units when you read of the disasters of the world and realize that the media often makes things sound worse, or less worse, than it actually is.


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