Owen Brian Toon (born May 26, 1947 in Bethesda, Maryland)[1] is an American professor of atmospheric and oceanic sciences.

His research on the asteroid impact that killed the dinosaurs led to the discovery of nuclear winter due to the major decrease in temperature.

[3] The effects of nuclear winter were re-examined in a 2006 presentation at the annual meeting of the American Geophysical Union in San Francisco, where Toon and colleagues found that even a regional nuclear war could prove deadly for a large number of people.

[4] They calculated that as few as fifty detonations of Hiroshima-size bombs could kill as many as twenty million people, although it would not produce a nuclear winter.

[5] The atmospheric effects of a regional nuclear war would last several years, and would be strongest at mid-latitudes, including the United States and Europe.