What makes environmental systems so complex?

Environmental systems are so complex because it contains so many parts that would have to interact to each other and that would affect the system as a whole. In environmental systems, it consists of traditional natural sciences, economic, politics, law, and many others. Although, this  system is only a small part of what we called a universe- a collection of different systems, it still has various and numerous smaller parts that are related to one another that keeps every process or activity going. Most of these smaller parts are uncontrollable and unpredictable which makes it more complex than it really is.