John Ten Hoeve and Mark Z. Jacobson predicted how the radioactive material spread using an atmospheric model and estimated how many people would have been exposed to that radiation. They reported their results in the journal Energy and Environmental Science on Tuesday.
They acknowledged that their estimates have a widely variable range, due to the limitations of their model.
Overwhelmingly, Japan had the most affected people, according to the results. Hoeve and Jacobson's model predicted somewhere between 0 and 12 deaths and 0 and 30 cancer-related deaths in the U.S. as a result of the disaster.
These worldwide values are relatively low, Ten Hoeve said in a statement Tuesday. He said the results serve to manage the fear in other countries that the disaster had an extensive global reach.
The researchers say the Japanese government's rapid response, including evacuating people in a 20-km radius around the plant, distributing iodine tablets and curtailing crop production where elevated radiation was detected, probably helped lessen the cancer risk for the populace.
However, the researchers noted that while according to their model, the evacuation prevented up to 245 radiation-related deaths, nearly 600 people -- mostly elderly and sick -- died during the evacuation process of other causes. (The researchers cautioned against drawing too many conclusions about evacuation procedures based on their model, with Jacobson explaining that You still have an obligation to evacuate people according to the worst-case scenario.)
Jacobson and Ten Hoeve also noted that any projected mortalities from radiation are dwarfed by the casualties from the earthquake and tsunami - currently estimated at around 20,000 - and is still smaller than the casualties caused by the 1986 Chernobyl nuclear accident.
Nevertheless, long-term cancer risk studies should be conducted in Japan to compare with the estimates developed here as well as with future modeling studies of the health effects from Fukushima, they wrote.
In March, a team of Japanese scientists reported in Nature the results from an examination of 62 Fukushima evacuees looking for signs of radiation exposure. In 46 of the subjects they found evidence of radioiodine activity in their thyroid.
The researchers estimated that the median dose the Fukushima evacuees experienced was 4.2 millisieverts (mSv) and 3.5 mSv in children and adults, respectively. That dose isn't exactly excessive, as an average U.S. resident is exposed to about 3 mSv of radiation each year. Meanwhile, residents directly affected by the Chernobyl accident had an average thyroid dose of 490 mSv.