Most fundamentally, engineers practice the art of building practical models to solve concrete problems. You might suppose that the models used in environmental science are normally complex because the environmental processes involved are almost always complex. It is true that complex models, such as General Circulation Models of the atmosphere, are essential tools, in their place. However, such models are extra-ordinarily expensive to build and use. As a practical matter, we always start out, and often finish, using simple models, even when we know the problem is complex in principle.
Engineers call such models back of the envelope calculations.
The idea is to try to boil a complex problem to a simplicity that lies at its heart. You try to make some conservative simplifying assumptions, perhaps heroic simplifying assumptions. This often requires the killer instinct a willingness to ignore all sorts of possible objections to get to some kind of model you can solve to get some kind of answer, any kind of answer. Then you turn the crank , and see what sort of answer pops out. Then you ask if the answer is reasonable.