Page 50 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

14 Chapter 1 essentials of Geography
Steady State Equilibrium
System fluctuates around a stable average and maintains same operation level
(a)
Passage of time
Dynamic Equilibrium
System fluctuates around a stable average, but exhibits a trend overall
Threshold, or “tipping point”
System jumps to a new stable average condition
(b)
Passage of time
(c) Wave action, heavy rainfall, and frost action caused this slope failure at the Cliffs of Dover, England, in March 2012. When a strength threshold was exceeded, the collapse occurred and the cliff edge retreated several metres.
▲Figure 1.9 System equilibria: steady-state and dynamic. The vertical axis represents the value of a typical systems variable, such as stream channel width or hillslope angle. [(c) Rex Features/AP Images.]
a tipping point, with increased extinctions since 1986 re- lated directly to climate change; discussed in Chapter 19 and GeoReport 1.2.
Models of Systems A model is a simplified, idealized representation of part of the real world. Scientists design models with varying degrees of specificity. A conceptual model is usually the most generalized and focuses on how processes interact within a system. A numerical model is more specific and is usually based on data collected from field or laboratory work. The simplicity of a model makes a system easier to understand and to simulate in experiments. A good example is a model of the hydrologic system, which represents Earth’s entire water system, its related energy flows, and the atmosphere, surface, and subsurface environments through which water moves (see Figure 9.4 in Chapter 9). Predictions associated with climate change are often based on computer models of
atmospheric processes, discussed in Chapter 11. We dis- cuss many system models in this text.
Adjusting the variables in a model simulates differ- ing conditions and allows predictions of possible system operations. However, predictions are only as good as the assumptions and accuracy built into the model. A model is best viewed for what it is—a simplification to help us understand complex processes.
Systems Organization in Geosystems
From general layout to presentation of specific topics, Geosystems follows a systems flow. The part structure is designed around Earth systems pertaining to air, water, land, and living organisms. These are Earth’s four “spheres” and represent the broadest level of orga- nization within the book. Within each part, chapters and topics are arranged according to systems thinking,
Georeport1.2 AmphibiansatThresholds
Amphibian species are a threatened group of animals, with approximately one-third of recognized species now at risk of extinction. According to the International Union for Conservation of Nature (IUCN) Amphibian Specialist Group, two new
initiatives are aimed at stopping the amphibian decline: increased habitat protection for species that are found in only a single location and stepped-up efforts at testing antifungal drugs to halt the killer frog disease favoured by the temperature increases. Read more about the current amphibian extinction crisis at www.amphibians.org/.