At the scale of the planet, these systems are closed. On a regional scale, however, matter flow systems may be open and materials may accumulate to the benefit or detriment of various ecosystem components. Thus, the ideas of closed and open systems focus attention on the finite nature of the earth-atmosphere system and on the processes that transport matter from place to place within it. Yet another important systems concept is that of feedback and equilibrium. Both are related to change in systems with time.
Climate systems provide a good example.
Present observations and models indicate that clouds form a positive feedback loop in global surface temperature, so that when surface temperature increases, high clouds accentuate the greenhouse effect and enhance the warming. This case documents how systems thinking is important in understanding global change phenomena. Finally, the systems approach helps us convey to students a true understanding of how physical geographers study physical processes. Because we study earth and life phenomena, our ability to conduct experiments is limited. Instead, we must do our work largely by treating the earth as our laboratory-that is, by observing the earth and its processes at times and places and on different scales.