The Quaternary Period is classified by the series of glaciations there have been and also the increase and development of what are anatomically modern day humans. The first is basic, but to explain it a bit I would say that this period has had periods of increased and decreased coolness and glaciation. The period we are in now expanded from approximately 2.5 million years ago to today, and only today are we seeing things that were not the norms of previous years. For example, there have, as it seems, always been shifts between glaciers forming in northern Arctic and the southern Antarctic, but in periods of more cooling we see the expansion of these glaciers. Then when the period comes to an end we see the rise in temperature, which lasts roughly 10,000 to 15,000 years, known as interglacial periods. Not all areas though were getting more glacial or less, some areas were characterized by more precipitation or less, and same for snow. The one blip, if you wanna call it that, which we see in the temperature is more recently, where there is a notice of pretty drastic rising in temperature and Carbon Dioxide levels. This period otherwise has been fairly consistent in glacial expanding and retracting, but the fear that many have is that humans affect the environment in such a way that alters climate drastically.
Sources:
http://science.nationalgeographic.com/science/prehistoric-world/quaternary/
http://qra.org.uk/about/quaternary
http://en.wikipedia.org/wiki/Quaternary
Figure 1: This is a graph depicting the current Quaternary Period that we are in, spanning over the last 2.5 million years. Notice how the trends of glacial and interglacial periods are distinct with the rising and decreasing temperatures, but with more recent years staying warmer.
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