Answer
Environmental changes will lead to evolutionary change if 1) there is genetic variation for traits which lead to adaptation to those conditions and 2) the changes can act on that variation to promote the survival and reproduction of better-adapted individuals. As an example, consider a great increase in snowfall in an area dominated by grasslands. If a population of rabbits includes some which are white they will have a selective advantage during the winter since they, and not their brown cousins, will be camouflaged against the snow and less likely to be eaten by predators. Without that variation no amount of snow or predation will turn brown rabbits white, and without the predators there is no selective advantage to being the color of the snow. The speed of the change in the population towards white color will depend on whether white is dominant (quicker) or recessive (slower).
Work Step by Step
Use you imagination to select your example-- perhaps skim the textbook for a likely case. Then see what the selective force in your example is,what kills some phenotypes but not others. Also ask yourself what variation there is in your proposed case. Be sure that it has a clear genetic basis since that is required for evolutionary change.
