Nature News and Columbia University have joined forces to make a Google Earth map showing the world populations at risk from nuclear fallout. The interactive map combines data on population and the locations and sizes of reactors, plotting risk graphically in the form of circles. Small, green circles represent relatively low risk, based on population size near the nuclear plants; mid-sized yellow circles represent greater risk, with large red circles representing the greatest risk.

Nature News which has an excellent article accompanying the feature, acknowledges that the calculus of nuclear risk is much more complex than population size. What are the external threats to a plant? (Though bear in mind the Fukushima Daiichi plant was considered as having a "relatively low chance" of sustaining major earthquake or tsunami damage, says Nature.) How large is the plant, and thus its possible fallout—and could multiple reactors develop crises at once, as was the case at Fukushima? Finally, but perhaps most importantly, is there a "culture of security" at a given plant? Each of these factors is essential.

That last one in particular, is intriguing. "One flaw that I worry about is that of overconfidence," one expert said to Nature. Building a "culture of security" is difficult; maintaining one even harder. "It is expensive. And it involves an attention to detail and a willingness to accept and learn from intrusive peer review by others,"griped the chair of an International Nuclear Safety Advisory Group in a recent report. Intriguingly, plants that are in their middle age, so to speak, are safer than brand new plants (where user error is more likely) or aging plants (predictably, since they're more worn and torn). Engineers call this dip and rise in risk the "bathtub curve."

Still, once you bear all these complex factors in mind, there's one very stark, simple metric by which you can assess risk: population size. Once the disaster is underway, that's the metric you're going to wish you had paid the most attention to. Which is why the new Google Earth map is startling.

The world has 211 nuclear power plants. They fleck the map, clustered in predictable places: America (the northeast, mostly), Europe (all over, including Eastern Europe and Russia), and much of Asia and India. There's just one if Africa (South Africa) and two in South America (Argentina and Brazil), from the looks of it. In some places, the numbers that underlie the dots are harrowing. The Guandong plant not far from Hong Kong has more than 28 million people living within 75 kilometers of a dual-reactor plant. One hundred fifty-two plants have over a million people within 75 kilometers. Even constricting the radius to a smaller number, 30 kilometers, the numbers are still frightening: one Taiwan plant has 5.5 million people that close by, while another has 4.7 million. The city of Taipei could be within the fallout zone if either of those plants had a meltdown. In Karachi, Pakistan, 8.2 million people live within 30 kilometers of a nuclear plant (albeit a relatively small, 125-megawatt plant).

You can find the interactive map here (you may need to download a plug-in). After grabbing and scrolling around for a moment, looking at all the yellow, orange, and red circles that dot the globe like warning lights, you zoom in and realize something. The circle over Fukushima is green.

Republished with permission from Authored by David Zax. Photo, top, via