The Earth's climate represents a holistic system, with mutually interacting components ranging through a host of specialized sub-disciplines. Rarely are there simple answers to climate problems, as the multiple feedbacks can lead to a variety of results. Therefore, to understand what has happened in the past, and what will happen as greenhouse gases continue to accumulate in the atmosphere, requires a familiarity with the various aspects of the system, utilizing everything we have available — observations, theory, and computer modeling. It requires interacting with atmospheric scientists, oceanographers, specialists in polar processes, cloud physicists, hydrologists, land surface biologists, atmospheric chemists, computer scientists, etc. To understand the potential impacts of climate change requires further interactions, with agronomists, economists, demographic specialists, etc. As you can see, the climate system and climate change is a great integrator of knowledge, and requires a multi-disciplinary approach.
In my research it is necessary to become familiar with these various disciplines and put the knowledge into common form, via building and utilizing climate models. Such models can be used to study why the Last Ice Age arose, why the dinosaurs disappeared, and where would be the best place to live in 2100, climatically-speaking. The fact that as of yet we do not have convincing answers to any of these questions should only serve as motivation - one wouldn't want to enter a field in which everything is known! Climate studies represent an exciting and highly topical challenge, and what we learn can affect public policy and mankind directly.