It may result from great fires, wind, and large quantities of smoke and dust.  
The possibilty of this phenomenon was discussed in a famous report by Turco, Toon, Ackerman, Pollack, and Sagan.  It may result from great fires, wind, and large quantities of smoke and dust.  Theoretically, these effects could reduce incoming solar radiation, resulting in the extreme cooling of the earth's surface, possibly to -15 to -25 Celsius.  FTP, name this two-word "seasonal" term, described as a severe deterioration of climate that might take place as a result of multiple H-bomb explosions on the earth's surface.
The possibilty of this phenomenon was discussed in a famous report by Turco, Toon, Ackerman, Pollack, and Sagan.  
Nuclear Winter