The advantage of shedding broad leaves in the winter is to conserve the energy that needs to expand in order to provide heat to each part of the plant including leaves as in winters it becomes very dry and cold. If they do not shed their leaves they have to spend more energy to spend energy on leaves.
Needles like leaves have a thick cuticle layer that prevents from losing water in dry conditions or conditions with a limited amount of water in the soil. These leaves also help in photosynthesis by capturing more sunlight as they have a larger surface area. These adaptions can live in poor soil, rain and snowy conditions.
Ice ages have occurred in the earth history and do occur more or less regularly in a cycle. It is believed that ice ages are as a result of small changes in the earth's orbit and also dependent on the solar cycles. The temperatures on the earth reduce causing the ice sheets in the poles to extend to the subtropics.
