I agree with you spring that its Fukishima radiation, but jem does raise a very valid point. At cruising altitude the radiation in the atmosphere is give or take 50 to 80 times what it is at sea level. The aircraft shields most, but not all of it. If the Sun is throwing out a greatly increased AMT of rads its reaching us on Earth. Further, Haarp et. all may also come in play.
edit: curious and went to look, this story says 64x at 39,000 ft. Obviously most of which is shielded by the aircraft but assuming consistency the rad meter did bump 400%. Never a good thing unless you're trying to 'fry' batman.
http://www.sciencedaily.com/videos/2005/0907-flying_and_radiation_risk.htm