The most likely scenario is:
The proportion of white-furred rabbits in the population declines.
This is because white-furred rabbits are typically better adapted to cold, snowy environments, where their coloration provides camouflage against predators. As the average temperature increases and winters become shorter (leading to less snow cover), brown-furred rabbits, which are better camouflaged in a warmer, less snowy environment, are likely to thrive more than white-furred rabbits. Thus, the proportion of white-furred rabbits would likely decline.