I ejaculated on my shorts in a cold environment and took them off for 12 hours, i put them on again, can sperm still have been alive after those 12hr?

Possible by unlikely: Sperm do not live long outside of the male body. In the female genital tract they can live for about 24 hours. Being in a cold environment makes it even less likely that a sperm survived. However, if your question is regarding whether or not it could possibly lead to a pregnancy, it is therhetically possible, but very very unlikely. There are millions of sperm in an ejaculate and only 1 is needed.