Japan's nuclear crisis may yet get as bad as some have been saying, but, until then, some facts and perspective...
The average natural background radiation level is 2,400 microsieverts per year.
Human-caused radiation contributes about 5 microsieverts per year, from atmospheric nuclear bomb tests, nuclear power plant accidents, medical tests, and coal-fired plants.
World-wide, coal-fired power plants are estimated to cause some 320 deaths per year from radiation-induced cancer.
China has 20,000 coal mining deaths every year.
Some experts estimate that chemical and particle coal smoke pollution kills 30,000 per year in the U.S.
Japan’s earthquake and tsunami death toll: almost 10,000 with 13,000 missing and likely dead.
Residents of Ramsar, Iran experience 260,000 microsieverts per year of radiation due to high levels of dissolved radium-226 in water in local hot springs. Interestingly, no ill-effects have been seen in Ramsar due to the "radiation paradox."
Background radiation is greater at higher altitudes: Denver gets about twice as much radiation as New York.
Taking a bizjet over the pole at 51,000 feet results in a radiation exposure 800 times above average: about 219 microsieverts per hour.
The heavily damaged Fukushima nuclear plant in Japan on Tuesday saw radiation levels of 240 microsieverts per hour at the front gate, a bit more than the 219 microsieverts per hour rate of a bizjet flying the polar route.
Thus, radiation at Fukushima that day was about 1,000 times above “normal” or, about 20 percent higher than the dose rate of flying over the North Pole in a business jet at 51,000 feet.