Final answer:
The number of frost days is likely to decrease by 2100 AD, according to the IPCC AR4 multimodel climate projections.
Step-by-step explanation:
The IPCC AR4 multimodel climate projections suggest that the number of frost days is likely to decrease by 2100 AD. With the projected increase in global temperatures, the frequency of frost days is expected to decline. This is because warmer temperatures lead to less freezing conditions and therefore fewer frost days.